Tierärztliche Hochschule Hannover
Institut für Zoologie
Geographical variation in the granular
poison frog, Oophaga granulifera:
genetics, colouration, advertisement call
and morphology
DISSERTATION
zur Erlangung des Grades
eines Doktors der Naturwissenschaften
– Doctor rerum naturalium –
(Dr. rer. nat.)
vorgelegt von
Oscar Brusa
Cuggiono, Italien.
Hannover 2012
Wissenschaftliche Betreuung:
Prof. Dr. Heike Pröhl
1. Gutachterin:
Prof. Dr. Heike Pröhl
2. Gutachter:
Dr. Sebastian Steinfartz
Tag der mündlichen Prüfung:
21 September 2012
Eidesstattliche Erklärung
Hiermit versichere ich, dass ich die vorliegende Arbeit selbständig und nur mit den
angegebenen Hilfsmitteln angefertigt habe. Alle Stellen, die dem Wortlaut oder Sinn
nach anderen Werken entnommen sind, wurden durch Angaben der Quellen als
Entlehnungen kenntlich gemacht.
Ich versichere, dass die vorliegende Dissertation nicht woanders eingereicht wurde.
Hannover, den 14/7/2012
Oscar Brusa
To:
All people who dream.
Table of contents
Zusammenfassung
9
Summary
11
1. Introduction
13
1.1 Biological species concept and speciation mechanisms
13
1.2 Geographic variation in animals
14
1.3 Aposematism
18
1.4 The remarkable case of polymorphic toxic species
19
1.5 The biogeographical peculiarities of the lower Central American
21
1.6 Evolutionary studies on amphibians in lower Central American
23
1.7 Neotropical poison-dart frogs
25
1.8 The granular poison-dart frog, Oophaga granulifera
28
1.9 Aims of the study
29
1.10 Study Area
31
2. Material and Methods
33
2.1 Field activity
33
2.2 Tissue sampling and DNA extraction
33
2.3 Phylogeography
34
2.3.1 Mitochondrial DNA sequencing
34
2.3.2 Mitochondrial DNA analyses
35
2.4 Population genetics
2.4.1 Microsatellite loci genotyping and analyses
37
37
2.5 Colour description and measurements
38
2.6 Bioacoustics
38
2.7 Morphology
39
3. Results
40
3.1 Colouration
40
3.2 Mitochondrial DNA variation and divergence
46
3.3 Mitochondrial DNA phylogeography and population structure
48
3.4. Microsatellite loci variation and population structure
51
3.5 Bioacoustics
53
3.6 Morphology
57
4. Discussion
65
4.1 General discussion
65
4.2 Why should a cryptic morph evolve in an aposematic species?
70
4.2.1 General background
70
4.2.2 Role of genetic drift
71
4.2.3 Role of predation
71
4.2.4 Role of toxicity
73
4.2.5 Role of sexual selection
75
5. Conclusion
76
6. References
77
Additional Information
110
1. Sequences accession numbers
110
2. Population structure ∆K results
113
Ackowledgments
114
9
Geographische Variation in dem granulierten Giftfrosch,
Oophaga granulifera: Genetik, Färbung, Paarungsrufe und
Morphologie.
Oscar Brusa
Zusammenfassung
Die vorliegende Arbeit untersucht die intraspezifische genetische Divergenz und phänotypische
Diversifizierung des neotropischen Giftfrosches, Oophaga granulifera, innerhalb seines
Verbreitungsgebietes. Dabei werden phylogeographische Muster, Populationsstrukturen und
phänotypische Merkmale, die potentiell an reproduktiver Isolation beteiligt sind, analysiert. Die
Analysen zur Phylogeographie and der Populationsstruktur wurden mit Hilfe der
mitochondrialen Gene von Cytochrom b und 16S sowie sieben polymorphen MikrosatellitenLoci von neun bis elf Populationen durchgeführt. Für die Analyse der Phänotypen erfasste ich
den Farbphänotyp in 189 Fröschen und maß die Reflektionsspektren in fünf ausgewählten
Populationen. Zudem wurden in zehn Populationen männliche Paarungsrufe aufgenommen und
zehn morphologische Parameter gemessen. Die phylogenetische Rekonstruktion unterstützte die
Aufspaltung in eine südliche und eine nördliche mitochondriale Linie von O. granulifera. Dieses
Ergebnis wurde durch die Mikrosatelliten-Analyse bestätigt. Weiterhin zeigt die Art
hauptsächlich zwei dorsale Farbvarianten, rot im südlichen und grün im nördlichen
Verbreitungsgebiet. Die Verteilung von Farbmorphen ist asymmetrisch zur mitochondrialen
Variation. Die südliche Linie umfasste nur monomorphe rote Populationen, wohingegen die
nördliche Linie rote, grüne und polymorphe Populationen enthielt. Die polymorphen
10
Populationen kommen in einer Übergangszone zwischen den beiden wichtigsten Farbmorphen
vor. Hier traten neue graduell intermediäre Farbmorphen, von orange-selb bis grün-braun,
zusammen mit roten oder grünen Fröschen auf. Trotzdem folgte der Übergang von rot nach grün
keiner einfachen geographischen Kline. Das Vorkommen von graduell intermediären
Farbmorphen deutet auf signifikante Vermischung entlang der Übergangszone hin. Beide
genetischen Linien unterschieden sich signifikant in ihren Paarungsrufen und ihrer Morphologie.
In der nördlichen Linie unterschied sich die rote Farbmorphe von der grünen Farbmorphe in der
Pulsrate der Paarungsrufe und in der Körpergröße. Die Unterschiede in den Lauten und der
Morphologie beider Farbmorphen liefern Potential für „assortative mating“, wobei zueinander
passende Partner bevorzugt werden. Die mehrfachen Hinweise auf die tiefreichende
intraspezifische Divergenz deuten stark darauf hin, dass es sich bei den beiden identifizierten
Linien um verschiedene Arten handelt. Dem gegenüber lässt sich aufgrund der fehlenden
genetischen Diversifizierung zwischen den Farbmorphen innerhalb der nördlichen Linie und der
genetischen Zusammengehörigkeit der Übergangszone auf eine erst kürzlich aufgetretene
Diversifizierung
der
Körperfärbung
schließen.
Ausgehend
von
einer
Süd-Nord
Ausbreitungsbewegung sind unterschiedliche lokale Selektionsdrücke der Schlüssel zur
Interpretation der beachtlichen Farbvariation in diesem aposematischen System.
11
Geographical variation in the granular poison frog, Oophaga
granulifera: genetics, colouration, advertisement call and
morphology.
Oscar Brusa
Summary
The present work investigates the intraspecific genetic divergence and phenotypic
diversification in the neo-tropical poison frog, Oophaga granulifera, across its distribution
range, analysing phylogeographic patterns, population structure and phenotypic traits
potentially involved in reproductive isolation. The phylogeographic and population structure
analyses were performed using the mitochondrial genes cytochrome b and 16S and seven
polymorphic microsatellite loci from nine to eleven populations. For phenotypic analysis, I
observed the colour phenotype in 189 frogs and measured the reflectance spectra in five
targeted populations. Moreover, male advertisement calls were recorded and ten
morphological variables measured in ten populations. The phylogenetic reconstruction
supported the divergence into southern and northern mitochondrial lineages in O. granulifera,
which was confirmed by the microsatellite analyses. The species presents two main dorsal
colour morphs, red in the south of the distribution and green in the north. The distribution of
colour phenotypes is asymmetric as compared to the mitochondrial variation. The southern
lineage included only monomorphic red populations while the northern lineage contained red,
green and polymorphic populations. The polymorphic populations occured in a transition area
between the main morphs in the northern lineage. Here novel gradual intermediate colour
12
variants, varying from orange-yellow to green-brown, occurred with the red or green
phenotypes. However the gradual change from red to green did not follow simple linear
geographic colour cline. The occurrence of these intermediate morphs suggests the presence
of gene flow between the red and green morphs as confirmed by the significant admixture
across the transition area. The two genetic lineages significantly differed in advertisement
calls and morphology. The red and green colour morphs in the northern lineage differed in
pulse rate of the advertisement call and body size revealing potential for assortative mating.
In conclusion, multiple lines of evidence show that O. granulifera presents deep intraspecific
divergence strongly suggesting that the two identified lineages may well represent different
species. On the contrary, the lack of genetic diversification among colour morphs within the
northern lineage and the genetic connectivity across the colour transition area suggest a recent
colour diversification. Originating from a south-north colonization movement, locally
diversified selection is likely to represent the key for interpreting the striking colour variation
in this aposematic system.
13
1. Introduction
1.1 Biological species concept and speciation mechanisms
The scientific definition of species in biology is a complex matter not free from controversy.
The topic has been the object of extensive investigation and reviewing (Ereshefsky, 1992;
Mallet, 1995; Dover, 1995, Mayden, 1997; Burton, 2004; Coyne & Orr, 2004; Hausdorf,
2011). If we refer to sexual organisms, two species are considered distinguished when they
are reproductively isolated (Mayr, 1947, 1963, 1970). The reproductive isolation can be prezygotic (Bailey et al., 2004, Dopman et al., 2010) or post-zygotic (Sánchez-Guillén et al.,
2012). Pre-zygotic mechanisms avoid interbreeding among populations and the consequent
gene exchange through behavioural, physiological or morphological divergence (Schluter,
2001, 2009; Fitzpatrick et al., 2009). If the reproductive isolation persists over time, postzygotic isolation characterised by sterility or inviability of hybrids may arise following the
accumulation of genetic differences (Welch, 2004; Orr & Turelli, 2001). Genetic drift and
natural selection play an important role in speciation acting at pre- and post-zygotic levels
(Lande, 1976; Templeton, 1981; Schluter, 2001). Sexual selection is the other key factor able
to drive population differentiation, typically at the pre-zygotic stage (pre and post-mating)
(Noor, 1999; Panhuis et al., 2001; Kirkpatrick & Ravigné, 2002), through a differential
reproductive output among individuals determined by mate choice, mostly by females, that
determines a selective pressure on the opposite sex (Lande, 1981; Panhuis et al., 2001). The
speciation process is also influenced by the geographic distribution of the diverging
populations. Three biogeographic mechanisms of species formation have been identified:
allopatry (Feder et al., 2003; Kirkpatrick & Barton, 2006; Feder & Nosil, 2009), parapatry
(Gavrilets et al., 2000; Turelli et al., 2001; Doebeli & Dieckmann, 2004) and sympatry
14
(Schliewen et al., 2006; Barluenga et al., 2006; Mallet et al., 2009). If different populations
are separated by a large distance as compared to the species vagility or an insurmountable
physical barrier such as a river or a mountain range, that is allopatry by definition. Allopatric
speciation is a classic model and there is convergence among scientists on its importance in
speciation. Parapatric speciation occurs to populations occupying adjacent areas following
behavioural or ecological diversification. Sympatric speciation concerns populations found in
the same area when reproductive isolation arises by natural or sexual selection (White, 1968,
Endler, 1977; Feder et al., 2005; Barluenga et al, 2006). Sympatric models have been
supported by some studies (Schliewen et al., 2006; Barluenga et al., 2006; Mallet et al., 2009)
but the possibility that populations may diverge in the presence of potential gene flow is not
universally accepted (e.g. Fitzpatrick et al., 2008).
1.2 Geographic variation in animals
Intraspecific geographical variation in animals is a widespread phenomenon closely linked to
the speciation process (Mayr, 1942; Gould, 1972; Endler, 1977; Coyne & Orr, 2004). For
instance, populations or individuals occurring in different areas diverge in morphology
(Grant, 1999), colour (Zink & Remsen, 1986) or calls (Wilczynski & Ryan, 1999).
Geographical variation in body size and body shape has been reported in all vertebrate taxa
including, amphibians [e.g. newts (Arntzen & Wallis, 1999); anurans (Castellano & Giacoma,
1998; Schäuble, 2004)], birds [e.g. barnacle goose (Larsson & Forslund, 1991); Galapagos
finches (Grant & Grant, 1989)], mammals [e.g. bats, (Marchan-Rivadeneira et al., 2012);
rodents, (Colangelo et al., 2010)], reptiles [e.g. lizards, (Wiens et al., 2002; Malhotra &
Thorpe, 1997], fish (e.g. Barlow, 1961). Colour variation has been observed as well in several
species [e.g. fish (Kohda et al., 1996); amphibians (Hoffmann & Blouin, 2000); birds (Hill,
1993); reptiles (Rosenblum, 2004); mammals (Hoekstra et al., 2004)] and variation in
15
acoustic signals was found in amphibians (Gerhardt & Huber, 2002) and birds (Slabbekoorn
& Smith, 2002). In anurans, body size is relatively conserved within species (Cherry et al.,
1978; Green, 1993) but may vary along habitat, altitudinal and latitudinal gradients (Berven,
1982; Morrison & Hero, 2003; Rosso et al., 2004). Measuring variation in body size across
historically divergent lineages allows to infer whether population differences are explained by
geographical isolation alone, or whether localized selection contributes to fine-scale
population variation. Colouration and male advertisement calls are often heritable and subject
to selection (Endler, 1992; Ryan et al., 1996; Kingston et al., 2003; Hoekstra et al., 2004;
Hoffman et al., 2006). In polychromatic species individuals of the same sex and age display
colour variants that originate from the interplay between genetic and environmental
components (Roulin, 2004). Colour polymorphism can arise and be maintained by different
evolutionary processes. For instance, a reduction in gene flow among ecologically distinct
populations can lead to phenotypic divergence (Gray & McKinnon, 2006; Rueffler et al.,
2006). Similarly, male advertisement calls can diverge as a result of local adaptation (WestEberhard, 1983; Ryan & Wilczynski, 1991; Panhuis et al., 2001; Couldridge & van Staaden,
2004). All these traits have a partial (body size and colour) or exclusive (call) signalling
function which is important in intraspecific communication, being therefore potentially under
sexual selection (Arak, 1983; Forester & Czarnowsky, 1985; Ryan & Rand, 1990; Ryan &
Wilczynski, 1991; Ryan, 1999; Gabor et al., 2000). Body size can have an effect on mating
selection when larger males gain primary access to preferred females through greater
competitive ability (Berven, 1981; Elwood et al., 1987; Harari et al., 1999; Gabor et al., 2000;
Fisher & Cockburn, 2006) or when females selectively mate with larger males likely to have
superior fitness (Wedell & Sandberg, 1995; Harari et al., 1999; Gabor & Page, 2003). On the
other hand, males can also mate selectively with larger females because of fecundity
advantages (Verrell, 1985; Olsson, 1993; Harari et al., 1999; Dosen & Montgomerie, 2005;
Preston et al., 2005). Mate selection based on colour has received a great deal of attention for
16
the conspicuous traits that can arise in males through the selective process. For instance, the
blue structural colour of crown feathers (reflecting also in the ultraviolet range) has a direct
fitness effect for male blue tits because the females prefer to mate with those having a higher
reflectance (Andersson et al., 1998). Carotenoid-based colour traits of males are also selected
by females, for example in birds (Hill, 1990; MacDougall & Montgomerie, 2003) and fish
(Endler, 1983; Seehausen & van Alphen, 1998; Van Oppen et al., 1998; Barluenga et al.,
2006). Studies have shown that these colour traits are a cue for foraging ability, immune
system efficiency and overall body condition, characterising an honest signal. This depends
on the fact that carotenoid pigments cannot be synthesised endogenously and are a limited
resource in the environment. Therefore, a bright carotenoid-based colouration can only be
obtained diverting these pigments from their immune function according to a trade-off
mechanism (Blount et al., 2003; Baeta et al., 2008). Overall, the phenotypic variation
observed across the distribution of an animal species may depend on different factors that can
be summarised into three main components: genetic drift (Wright, 1948), natural (Hoekstra et
al., 2004) and sexual selection (Tilley et al., 1990; Ryan et al., 1996). These factors can act in
combination (Kirkpatrick & Ravigne, 2002). Genetic drift was introduced by Wright (1948)
and represents the stochastic genetic variation in a population. As it can be intuitively
understood, genetic drift is conceptually the opposite of selection, because the latter
modulates the expression of a certain trait according to its fitness outcome. Despite a
controversial evaluation of the actual importance of drift in the phenotypic evolution of
animal populations (Coyne, 1992; Gavrilets, 1997) it is well established that in some
circumstances, when significant numerical reductions of populations occur, such as in islands’
colonization or after a bottleneck, random fluctuations in allele frequencies are able to
determine evolutionary effects (Mayr, 1963; Carson & Templeton, 1984). It seems likely that
a diversification process within a species that eventually leads to speciation may often depend
on an interaction between selection and genetic drift (Mayr, 1963; Carson, 1975; Templeton,
17
1980). For instance, local genetic drift may determine intraspecific divergence in temporarily
isolated populations (Wright, 1948; Avise, 2000) but prezygotic isolation mechanisms, such
as mate choice, are necessary to impede the possible hybridisation between the diverging
populations if gene flow is re-established (Lande, 1982; Panhuis et al., 2001). The
intraspecific divergence in selected traits and its importance for speciation is well documented
(Butlin, 1987; Endler & Houde, 1995; Boughmann, 2002). Nonetheless, the vast majority of
studies have analysed these traits independently while comprehensive integrative analyses of
phenotypic geographical variation and genetic differentiation are lacking. The importance of
geographical variation in advertisement calls and in visual signals and its role in reproductive
isolation has been shown in anuran amphibians (Blair, 1958; Littlejohn et al., 1968; Gerhardt
& Huber, 2002; Hoskin et al., 2005), but very few studies investigated the relationships
among clines in visual signals, acoustic signals and genetic population structure (Pröhl et al.
2006; Amezquita et al., 2009). It is important to understand that the quantification of
geographical genetic and phenotypic diversity among populations represents a valuable
approach to get insights into the historical roles of drift and selection and evaluate the
potential for population diversification and speciation (Foster & Endler, 1999; Panhuis et al.,
2001; Gray & McKinnon, 2006; Hoffman et al., 2006). As mentioned, phenotypic
differentiation may lead to intra-specific divergence when populations are geographically
isolated or under diversifying selection (Dobzhansky, 1940; Thorpe et al., 1995; Hoekstra et
al., 2005; Pröhl et al., 2006). Therefore, it is necessary to analyse the geographical variation
considering historical and recent factors to understand the relationship between phenotypic
differentiation and genetic divergence, (Lougheed et al., 2006). Despite a possible
discordance in terms of direction and rate of evolution (Marroig & Cheverud, 2001; Wiens &
Penkrot, 2002), when analysed conjunctly genetic and phenotypic traits can reveal patterns of
covariation providing information on the relative importance of gene flow and local selection
in shaping spatial and temporal diversification (Lu & Bernatchez, 1999; McKay & Latta,
18
2002; Thorpe & Stenson, 2003; Gübitz et al., 2005; Nosil & Crespi, 2006). Given the
numerous pathways for signal divergence, it is not surprising that differentiation in calls is
often observed at the population level (Ryan et al., 1996; Foster & Endler, 1999) as well as
among species (Blair, 1958; Sanderson et al., 1992; Roberts & Wardell-Johnson, 1995;
Parsons & Shaw, 2001; Smith et al., 2003). At both scales, behavioural and morphological
characters can retain evolutionary and phylogenetic signals therefore providing a valuable
integrative information in phylogeographic studies (de Queiroz & Wimberger, 1993; Foster &
Endler, 1999; Wiens & Penkrot, 2002; Price, et al., 2007).
1.3 Aposematism
Aposematic animals have conspicuous warning colour patterns informing predators that the
individual is toxic, unpalatable or otherwise unprofitable. The occurrence of species using
toxic or distasteful substances as a defence against predators is a known phenomenon,
observed for example in insects (Frazer & Rothschild, 1960) molluscs (Faulkner, 1992), frogs
(Daly, 1987) and snakes (Smith, 1977). These chemical defences are often associated with
bright colour making the bearer of such signals easily recognizable by potential predators
(Wallace, 1867; Poulton, 1890; Ruxton et al. 2004). The association of these two traits
constitutes the base for the evolutionary theory known as aposematism. The related scenario
is that a potentially costly trait (bright colour) evolved to maximise the effect of another
potentially costly trait (toxicity). Distastefulness and toxicity other than with a bright
colouration may also be coupled with other distinctive colour patterns, odours, sounds and
behaviours originating an overall conspicuous strategy aimed at maximising the efficacy of
the unprofitability signal to predators (Poulton, 1890; Cott, 1940; Edmunds, 1974). Both
theory and empirical evidences suggest that an effective warning signal should be easy to
detect, learn, recall and associate with the defence (Benson, 1972; Gittleman & Harvey, 1980;
19
Roper & Redstone, 1987; Guilford, 1990; Alatalo & Mappes, 1996; Gamberale-Stille &
Tullberg, 1999; Lindstedt et al., 2011). A key point of the aposematic theory (Müller, 1879) is
that populations of aposematic species should converge into one conspicuous phenotype
because in this way the predator will easily learn to avoid that specific colour, making fewer
recognition errors (e.g., Guilford, 1986; Mallet & Barton, 1989; Joron & Mallet, 1998;
Gamberale-Stille, 2000; Kapan 2001; Beatty et al., 2004; Rowland et al., 2007; but see Rowe
et al., 2004; Ihalainen et al., 2007). Accordingly, selection is expected to favour the most
conspicuous and most common colour morph and decrease variation in warning coloration.
On the contrary, the presence of polymorphic populations is considered evolutionary not
optimal because it would imply a longer learning time by the predator with consequent
potential detrimental effect on the aposematic species individual fitness. Being the bright
colour associated with toxicity it represents a signal that the bearer cannot manipulate. This is
the reason why aposematic colouration has been explained within the theoretical framework
of honest signalling (Blount et al., 2009). The described scenario applies if we consider the
evolution of bright colour successive to the evolution of toxicity. On the other hand, one
cannot rule out the possibility that the bright colour evolved first, independently by toxicity.
In this case, the bright colour would have made the animal more detectable and therefore
more exposed to predation attempts, making the phenotype counter-selected via natural
selection. Subsequently, to compensate for the higher predation pressure caused by a
conspicuous appearance, the species evolved a system of chemical defence so that to originate
a deterrent effect to the predator and re-establish an evolutionary optimal strategy.
1.4 The remarkable case of polymorphic toxic species
One of the most striking examples of divergence in visual signals in animals is colour
polymorphism, defined as the co-occurrence of different colour morphs in a population
20
(Müller, 1879). Colour polymorphism belong to a broader phenomenon definable as colour
diversity or polychromatism, that is the occurrence of intraspecific colour variation, at the
interpopulation but not necessarily at the intrapopulation level. As previously mentioned
colour traits may depend on structural characteristics of integuments or pigments or a
combination of the two (Auber, 1957; Sieffermann & Hill, 2003; Endler, 1983). There are two
major classes of pigments responsible for colouration in animals: melanins and carotenoids
(Griffith et al., 2006). Melanins are synthesised endogenously and are responsible for both
black (across taxa) and rufous (mammals and birds) colour background and patterning in the
variants of eumelanin and pheomelanin respectively (Roulin, 2004). On the contrary, animals
are not able to synthesise carotenoids de-novo and therefore depend on the diet for displaying
a colouration based on these pigments. Animals can produce red, brown, orange and yellow
pigmentation rearranging enzymatically the many molecular variants of carotenoids (over 600
split into two classes, xantophylles and carotenes). Colour diversity depends mainly on
pigments variation and is a relatively common phenomenon in vertebrates, observed for both
melanins and, less frequently, carotenoids (Roulin, 2004; Hoffman & Blouin, 2000). It is also
worth to mention a less common class of endogenously synthesised pigments called pteridines
that can originate a colour range overlapping with those dependent on carotenoids. Pteridines
have been found for example in wings of butterflies (Rutowski et al., 2005; Bezzerides et al.,
2007), skin of fish (Grether et al., 2001), amphibians (Obika & Bagnara, 1964) and reptiles
(Steffen & McGraw, 2006) and irises of birds (Hill & McGraw, 2006). Pteridines can be
synthetized in the body therefore they are not considered components of honest signalling
systems. A biochemical analysis able to discriminate between carotenoids and pteridines is
therefore necessary for a correct inference concerning the evolutionary ecology of
pigmentation. Notably, colour polymorphism has been observed in association with toxicity
challenging the Müllerian prediction of phenotypic convergence in aposematic species. In
fact, aposematic animals are usually chromatically monomorphic (Edmunds, 1974;
21
Greenwood et al., 1981). Nonetheless, colour polymorphism exists in aposematic insects such
as lepidopterans [(Brakefield & Liebert, 1985; Stimson & Berman, 1990 including Heliconius
butterflies (Mallet, 1986)] ladybirds (Hodek & Honěk, 1996; Povolný, 1999) and true bugs
(Heteroptera; Štys, 2004). Among vertebrates dendrobatid frogs provide the most significant
example, showing a striking array of colour morphs, (Daly & Myers, 1967; Summers &
Clough, 2001; Summers et al., 2003; Darst & Cummings, 2006). This unexpected pattern is
known, for example, in the strawberry poison frog [Oophaga pumilio (Schmidt, 1857)] whose
colour diversity spans the visual spectrum including even cryptic variants (Summers et al.,
2003; Pröhl & Ostrowski, 2011). The presence of cryptic morphs is surprising because
predators are thought to learn to avoid unpalatable prey faster if they are conspicuous rather
than cryptic (Gittleman & Harvey, 1980; Roper & Redston, 1987; Alatalo & Mappes, 1996;
Lindström et al., 1999a) and if they are clearly contrasted against the average background
(Roper & Redston, 1987; Lindström, et al., 1999a; Gamberale-Stille, 2001; Prudic et al.,
2007). Several factors have been taken into consideration to explain the occurrence of colour
polymorphism in aposematic species. These include: genetic drift (Mallet & Singer, 1987;
Turner & Mallet, 1996; Mallet & Joron, 1999, Rudh et al., 2007), sexual selection (Summers
et al., 1999, Maan & Seehausen, 2011), variation in toxin availability (Wang, 2011) and
variation in predation regime (Mallet & Joron, 1999; Endler & Mappes, 2004; Nosil et al.,
2005; Ratcliffe & Nydam, 2008).
1.5 The biogeographical peculiarities of the lower Central American region
The numerous studies carried out on Central America anuran amphibians have provided
insights into the great level of variation typical of this biogeographic region (Ryan et al.,
1996; Crawford, et al. 2007; Robertson et al., 2009). Due to its complex geomorphologic and
climatic history, Central America presents high biological diversity at the inter- and
22
intraspecific levels with the latter resulting in the evolution of different genetic lineages in
several species (Coates & Obando, 1996; Campbell, 1999; Kohlmann et al., 2002; Savage,
2002). Particularly, the history of Costa Rica and Panama has been profoundly influenced by
largescale landscape changes (Campbell, 1999; Kohlmann et al., 2002; Savage, 2002). A
fundamental geomorphologic trait of the area is the Cordillera de Talamanca, a mountain
chain extending across lower Central American that originated approximately 3 million years
ago dividing the area in Pacific and Atlantic slopes. This structure markedly altered the
geomorphology and climate of the Caribbean, Central and Pacific areas (Holdridge, 1947;
Campbell & Frost, 1993; Coates & Obando, 1996), producing a sharp geoclimatic
differentiation. This diversity likely contributed to the exceptionally high species richness and
endemicity characteristic of this area (Holdridge, 1947; Savage, 2002). The Cordillera de
Talamanca plaid a role in the diversification patterns across many Central American taxa
[terrestrial snakes (Zamudio & Greene, 1997; García-París et al. 2000); beetles (Kohlmann
et al. 2007); frogs (Crawford, 2003; Robertson & Robertson, 2008). In Costa Rica, the
southwestern region presents high level of endemism following the uplift of the Cordillera
and the consequent isolation from northwestern CR and Caribbean lowland forests
(Holdridge, 1947; Savage, 2002). Another biologically highly diverse area is the Osa
Peninsula, that may have derived from an offshore island drifted into mainland Costa Rica
approximately 2 million years ago (Kohlmann et al., 2002). Genetic isolation of the Osa
Peninsula populations from mainland Costa Rica has been documented in frogs (Crawford,
2003; Crawford et al., 2007; Robertson, 2008) and snakes (Zamudio & Greene, 1997). These
studies suggest that the Osa Peninsula has retained a signature of isolation, despite
reconnection to the mainland. In Panama, the Caribbean region of Bocas del Toro is a
significant biogeographic area for animal and plant taxa, including frogs (Crawford, 2003;
Weigt et al., 2005; Crawford et al., 2007; Hagemann & Pröhl, 2007).
23
1.6 Evolutionary studies on amphibians in the lower Central American
region
Studies conducted on amphibians of Costa Rica and Panama returned a complex picture of the
interplay between genetic and phenotypic diversification. For instance, populations of a
species may be phenotypically highly diversified despite a lack of concordant genetic
divergence as identifiable using nuclear and mitochondrial markers (Hagemann & Pröhl,
2007; Hauswaldt et al., 2011). On the contrary, populations rather similar in terms of
phenotype may be divergent when analysed at the molecular level (Hauswaldt et al., 2011;
present study). Therefore, a compelling aim of modern evolutionary studies is to clarify the
patterns of association between the variation in traits such as body size, colour, call and
historical and recent population genetic structure. This together with information on
ecological variation would allow to get insights into the possible evolutionary origin of the
stunning diversity of the area. Despite the need to consider all the relevant traits to have a
global description of the possible interrelations between genetic diversity and phenotype few
studies have really adopted a comprehensive approach. In the case of Neotropical anuran
amphibians, recent investigations have focussed on reconstructing the phylogeographic
patterns (Wang & Shaffer, 2008; Brown et al., 2010; Vences et al., 2003), some incorporated
data on recent population structure (Wang & Summers, 2010; Hauswaldt et al., 2011) and few
related those genetic traits to biological important components such as advertisement calls and
morphology (e.g. Pröhl et al., 2006; Amezquita et al., 2009). A clear example of the lack of
such a comprehensive approach is represented by dendrobatid frogs, that present a remarkable
colour variation occurring in some species, for instance in the Panamanian populations of the
strawberry poison frog Oophaga pumilio (Maan & Cummings, 2012). Several studies have
dealt with dendrobatids behaviour (Pröhl, 1997; Summers et al., 1999; Pröhl & Hödl, 1999;
Pröhl, 2003, 2005; Pröhl et al., 2007; Richards-Zawacki & Cummings, 2011), aposematic
defense evolution [using theoretical (Ruxton et al., 2004, 2007; Lee et al., 2011), empirical
24
(Maan & Cummings, 2008; Darst et al., 2006; Noonan & Comeault, 2009) and phylogenetic
approaches (Santos et al., 2003; Brown et al., 2010; Wang, 2011)] and the phylogenetic
relations within the Oophaga (former Dendrobates) genus (Hagemann & Pröhl, 2007;
Hauswaldt et al., 2011). Nonetheless, only a few studies have considered a key trait, for its
importance in intraspecific divergence, that is the male advertisement call (e.g. Pröhl et al.,
2007), that has been shown to play a role in mate choice at the population level in O. pumilio
(Pröhl et al., 2003) and in other Neotropical amphibians (Pröhl et al., 2006). It is also
remarkable that other traits potentially important in sexual selection such as morphology have
been quite neglected to date. Moreover, significant levels of genetic divergence were found
among populations of Costa Rica and Panama leading to the definition of different lineages in
some dendrobatid species (Symula et al., 2003; Noonan & Wray, 2006; Hagemann & Pröhl,
2007; Hauswaldt et al., 2011) as well as other amphibians (Ryan et al., 1996; Crawford et al.,
2007; Robertson et al., 2009). The complex paleogeographic history of the Neotropics
accounts for this high level of diversity (Lougheed et al., 1999; Graham et al., 2004; Elmer et
al., 2007; Roberts et al., 2007; Santos et al., 2009). The bright colour of many dendrobatids is
commonly associated with toxicity and explained according to the aposematism theory
(Summers & Clough, 2001; Darst & Cummings, 2006). Nonetheless, colour diversity among
populations and dull colour morphs exist (Savage, 1968). An instructive case is the strawberry
poison frog, Oophaga pumilio (Schmidt, 1857), that is monomorphic in Costa Rica but shows
a high number of colour morphs in Panama, in the Bocas del Toro archipelago (Daly &
Myers, 1967; Summers et al., 2003). A phylogeographic study found a southern and a
northern lineage with the former including all the polymorphic populations together with the
southern Costa Rica monomorphic populations (Hagemann & Pröhl, 2007). The presence of
two main lineages in O. pumilio has been confirmed by the bioacoustic divergence in the male
advertisement call (Pröhl et al., 2007). The importance of advertisement calls in anuran
reproductive isolation has been shown in several studies (Littlejohn et al., 1968; Gerhardt &
25
Huber, 2002; Hoskin et al., 2005). Nonetheless, there is a general lack of studies combining
phylogeographic reconstruction with an analysis of advertisement call variation in poison
frogs. Investigating the correlation between genetic distance and divergence in bioacoustic
traits is useful to evaluate the patterns of reproductive isolation and speciation (e.g. Pröhl et
al., 2006). In fact, a low level of genetic differentiation between colour phenotypes has been
observed (Hagemann & Pröhl, 2007; Wang & Shaffer, 2008; Brown et al, 2010; Hauswaldt
et al., 2011; but see Wang & Summers, 2010). In this scenario sexual selection is likely to
have played a key role in the fixation of the colour peculiarities of these populations, with
females preferring males of their local insular colour morph (Summers et al., 1999; Reynolds
& Fitzpatrick, 2007; Maan & Cummings, 2008; Richard-Zawacki & Cummings, 2010).
Despite the obvious phenotypic divergence, there is no clear evidence of genetic
differentiation between colour morphs in this species (Pröhl et al., 2007; Hauswaldt et al.,
2011 but see Wang & Summers, 2010). Moreover, in dendrobatid species, studies
investigating the correlation between the geographical variation in colour and other traits
potentially involved in reproductive isolation are scant. Colour variation in poison frogs has
been related to several factors such as local variation in the predator communities, toxin
availability and assortative mating based on colour and call traits (Summers et al., 1997,
1999; Speed & Ruxton., 2004; Darts & Cummings, 2006; Saporito et al., 2007a; Speed &
Ruxton, 2007; Maan & Cummings, 2008, 2012). Within this framework, it is particularly
important to investigate the genetic and phenotypic variation across the species distribution to
have a clear picture of population-level diverging patterns.
1.7 Neotropical poison-dart frogs
During the last three decades the scientific knowledge on dendrobatid frogs, commonly
known as poison-dart frogs, has increased significantly. The number of described species
26
exponentially grew over the years and 247 are presently recognized. Dendrobatids are found
in dense primary and secondary forests, open areas, mountains and lowlands, and occupy a
variety of aquatic, terrestrial and arboreal habitats, in Central and South America. They are
distributed from Nicaragua to Bolivia and the Atlantic coast of Brazil and from the Pacific
coast of South America to the French Antilles (Savage, 2002). Approximately one-third of the
known species of dendrobatids have toxins in special dermal glands and are able to release
these toxins through the skin (Savage, 1968; Silverstone, 1975). The name poison-dart frogs
derives from the tradition of the native tribe of the Emberá, inhabiting the Chocó region of
western Colombia, to poison their hunting blowgun darts using the skin secretion of three
dendrobatid species, Phyllobates terribilis (Myers et al., 1978), P. aurotaenia (Boulenger,
1913), and P. bicolor (Duméril & Bibron, 1841). These three species contain in their skin two
of the most powerful toxins known, batrachotoxin and homobatrachotoxin (Myers et al.,
1978). Over 450 different lipophilic alkaloids have been isolated from dendrobatids and 24
major structural classes were defined (Daly et al., 1999). Many of these compounds found
application in medical research (Daly et al., 1997, 2000; Daly, 1998). It is known that
dendrobatids are not able to synthesise their toxins de-novo but they take them from the diet.
However, the details on the sequestration mechanism are still unknown (Daly et al., 1994a).
The dietary sources of alkaloids identified so far are formicine ants, a siphonotid millipede,
melyrid beetles and scheloribatid mites (Daly et al., 1987; Saporito et al., 2003; Dumbacher et
al., 2004; Saporito et al., 2004; Takada et al., 2005; Saporito et al., 2007a), while the
remaining alkaloids are still unknown elsewhere in nature. The vast majority of dendrobatids’
alkaloids are lypophilic molecules but one hydrophilic alkaloid, called tetrodotoxin, has been
detected in Colostethus inguinalis (Cope, 1868) (Daly et al., 1994b). In addition to toxicity,
Neotropical poison-arrow frogs are characterised by many other peculiar traits (Daly &
Myers, 1967; Weygoldt, 1987).
Dendrobatids, differently from the vast majority of
amphibian species, are diurnal (except Aromobates nocturnus, critically endangered and
27
poorly known species found in north-west Venezuela), they present bright and dull colours,
conspicuous and cryptic behaviour, territoriality with aggressive defence observed in both
males and females and complex mating rituals (e.g., Silverstone, 1973; Wells, 1978, 1980a,
1980b, 1980c; Weygoldt, 1987; Zimmermann & Zimmermann, 1988; Summers, 1989;
Aichinger, 1991; Caldwell, 1997; Fandino et al., 1997; Juncá, 1998; Caldwell & de Oliveira,
1999; Summers et al., 1997; Summers et al., 1999; Siddiqi et al., 2004; Pröhl, 2005; Maan &
Cummings, 2008; Lüddecke, 2000; Bourne et al., 2001; Pröhl & Berke, 2001; Pröhl, 2003;
Narins et al., 2003, 2005; Summers & McKeon, 2004). They lay terrestrial eggs, either on the
ground or in water-filled leaf axils of phytotelmata plants (from the ancient greek phyto-,
meaning 'plant', and telma, meaning 'pond'). Many species are characterized by elaborate
reproductive behaviours, biparental care, eggs moistening, egg guarding, tadpoles
transportation on the dorsum of parent frogs and tadpole feeding with unfertilized oocytes by
the mother (genus Oophaga) and one or both sexes are involved in highly evolved parental
care (Weygoldt, 1980; Zimmermann & Zimmermann 1988; Pröhl, 2005). In many species,
the male advertises a reproductive territory by emitting a species-specific call and defending it
actively from conspecific male intruders (Pröhl, 2005). Despite a broad knowledge on the
different aspects of their biology, the phylogenetic relationships among dendrobatids at the
inter- and intraspecific level are not yet fully understood. Phylogenetic relationships have
been used to investigate the evolutionary origins of dendrobatid features (e.g., Summers et al.,
1999; Santos et al., 2003; Vences et al., 2003; Graham et al., 2004; Darst et al., 2005). The
growing awareness of the importance of well resolved phylogeny for dendrobatids has
recently brought to significant systematic revisions (e.g. Noonan & Gaucher, 2006;
Wollenberg et al., 2006; Grant et al., 2006; Santos et al., 2009).
28
1.8 The granular poison-dart frog, Oophaga granulifera
The granular poison frog, O. granulifera, shows a very limited distribution in south-central
pacific Costa Rica (Fig. 1). It inhabits the lowland forests of the pacific slope of Cordillera de
Talamanca in Costa Rica and possibly north Panama. It is endangered because of habitat
fragmentation and included in the IUCN Red List as a vulnerable species (IUCN Red List). In
the southern part of its distribution the species is characterised by a red dorsal patch and a pale
blue to grey colour on the remaining part of the body. The proportion of body area covered
with red increases from the south to the centre of the distribution. Three colour morphs were
known before the present study: a red colour morph in the south and central part of the
distribution, a green colour morph in the north and a yellow colour morph located in between
(Savage, 2002; Wang, 2011). The species was classified in the histrionica group (Myers et al.,
1984) together with other 8 species found in Costa Rica, Panama and Colombia [O. arborea
(Myers et al., 1984), O. histrionica (Berthold, 1845), O. lehmanni (Myers & Daly, 1976), O.
occultator (Myers & Daly, 1976), O. pumilio (Schmidt, 1857), O. speciosa (Schmidt, 1857),
O. sylvatica (Funkhouser, 1956) and O. vicentei (Jungfer et al., 1996). Currently the same
species are grouped in the Oophaga genus, a name that derives from the unusual feeding of
the tadpoles on unfertilized eggs provided by the mother (Grant et al., 2006). O. granulifera
(Taylor, 1958) shares several behavioural traits with the other Oophaga species, such as male
territorial behaviour, courtship behaviour and predominantly female parental care including
tadpole transportation and tadpole feeding (Goodmann, 1971; Crump, 1972; van
Wijngaarden, 1985; Bolaños, 1990; van Wijngarden & Bolaños, 1992; van Wijngarden &
Gool, 1994) other than tadpole morphological traits (Grant et al., 2006). However, it is rather
divergent from congeneric species in terms of bioacoustic properties of the male
advertisement call, particularly the length of the acoustic unit (call) within a call sequence
(Meyer, 1992, 1993). In addition, phylogenetic assessments concerning Oophaga spp. and
29
including a few samples of O. granulifera, found indications of a high genetic divergence of
the latter within the Oophaga genus (Clough & Summers, 2000; Hagemann & Pröhl, 2007).
Figure 1 Sampling localities of Oophaga granulifera. The populations from Wang (2011) are
marked with *. Population codes as in Table 1.
1.9 Aims of the study
In the work here presented, I investigated the phylogeography, the population structure and
the geographical variation in colour, advertisement call and morphology in the granular
poison frog, Oophaga granulifera (Taylor, 1958). I aimed at evaluating the relationships
between historical and recent genetic structure, colour diversity and geographical variation in
30
traits which are potentially involved in reproductive isolation such as male advertisement call
and morphology. In particular, I focused on populations located in a very narrow colour
transition area between the two main colour morphs red and green, where intermorph crossing
was expected and intermediate colour phenotypes were more likely to occur. This assumption
was strengthened by the description of an intermediate yellow phenotype (Savage, 2002;
Wang 2011). I aimed at clarifying which of two possible scenarios may describe O.
granulifera colour diversification: the presence of intermediate gradual phenotypes as a result
of gene flow among the main morphs or, alternatively, the occurrence of the three discrete
colour morphs in reproductive isolation. I analysed the colour variation across the transition
area using field observations and spectrometric measurements and estimate the
interpopulation gene flow using microsatellite loci. In addition, I studied the geographical
variation in male advertisement call and morphology as potential sexual signals involved in
mate choice, to investigate how they relate to genetic and colour variation. Recently, Wang
(2011) identified two monophyletic clades in the species, one of southern red populations and
one of yellow and green populations nested within a northern clade which also contains a red
population. The author considered nine populations: four southern red, one central red, two
northern intermediate yellow and two northern green (Fig. 1). I analysed the phylogeography
of O. granulifera including three newly found polymorphic populations occurring in the
colour transition area. I also considered seven other populations: one northern green, three
northern red located within 20 km from the transition area and three red from the Osa
peninsula in the south (Table 1; Fig. 1). This population sampling allowed a detailed
evaluation of the historical genetic divergence across the colour transition area. Moreover, I
analysed the male advertisement calls and the morphological characteristics of the different
populations as key factors in mating recognition and consequently in reproductive isolation, to
unravel the pattern of interactions between morphological differentiation and speciation.
Summarising, the present study applied an integrative approach based on phylogeographic
31
analysis, bioacoustic and morphological analyses, detailed colour phenotype observations and
spectral reflectance measurements. Here, I provide the most comprehensive reconstruction of
O. granulifera phylogeography to date, including populations containing previously
undescribed colour morphs. I clarified the existence of two deep genetic lineages within the
species supported also by the differentiation in the male advertisement calls and morphology.
1.10 Study area
The study was carried out in south-western Costa Rica sampling in the lowland forest along
the pacific coast. The study area extends from the Osa Peninsula in the south to the central
part of the Puntarenas province between the towns of Quepos and Parrita and is rather
diversified in terms of climate and vegetation cover. The Osa peninsula is the most pristine
area of Costa Rica, (hosting for example the Corcovado national park, a world known
biodiversity hotspot) characterized by an extensive forest coverage and a low urbanization.
The area between the towns of Palmar and Quepos is characterised by a high human impact,
deforestation and consequent habitat fragmentation. The surroundings of Quepos also host
extended oil palm plantations. On the study area, many rivers are present including the Rio
Térraba (Fig. 1), the largest of Costa Rica that divides the town of Palmar into two parts,
named Palmar Norte and Palmar Sur.
32
Table 1 Information for each study population: name, code, geographical location and
coordinates, number of individuals sequenced for 16S and cyt b and genotyped for
microsatellites, number of individuals captured for colour description, number of male
advertisement calls recorded and frogs measured for morphological analysis.
CR region
GPS
Cyt b
16S
Msats
Colour
Call
Morphology
VE
Osa Peninsula
N8°42.457–
W83°29,589
2
–
7
16
9
–
Charcos
CH
Osa Peninsula
N8°40.319–
W83°30.320
3
3
8
19
8
19
Neotropica
NE
Osa Peninsula
N8°42.082–
W83°30.783
–
–
8
24
15
15
Palmar
PA
South-West
N8°58.112–
W83°27.356
3
3
7
14
4
14
Firestone
FS
Central-West
N9°16.668–
W83°52.167
3
2
8
15
5
15
Dominical
DO
Central-West
N9°15.065–
W83°51.292
3
2
8
15
–
–
Baru
BA
Central-West
N9°16.416–
W83°52.464
3
1
8
14
5
13
Matapalo
MA
Central-West
N9°20.913–
W83°52.167
4
1
10
20
3
20
Portalon
PL
Central-West
N9°20.951–
W83°56.277
3
2
15
19
4
19
Savegre
SA
Central-West
N9°22.039–
W83°58.277
1
1
8
20
6
19
Damitas
DA
North-West
N9°32.124–
W84°12.222
3
1
11
13
–
13
Population
Code
Ventana
33
2. Material and Methods
2.1 Field activity
The data used in the present study were collected during three field seasons from 2008 to
2010 for a total of seven months. The work was carried out between April and July in the first
half of the rainy season when the frogs calling was intense. According to the frogs activity
field work was performed in most cases from 5:00 am in the morning to 1:00 pm when
temperature increased and the calling activity became weak. Data collection was also
performed during minor activity time of Oophaga granulifera in late afternoon until sunset. In
case of precedent very abundant rainfall or slight rain during the day, frogs remain active
throughout the day enabling continuous data collection.
2.2 Tissue sampling and DNA extraction
Tissues samples used for genetic analyses were obtained in the field by toe-clipping and
stored in 96% ethanol in 1.5 ml plastic tubes with screw cap. Toe-clipping is the removal of
one or more toes and is a common practice in amphibian studies (Hero, 1989; Waichman,
1992; Halliday, 1996). Other than for obtaining tissue for genetic analyses it is used to allow
individual recognition in behavioural studies removing several toes in specific combinations
and to obtain bone for estimating age using skeletochronology (Friedl & Klump, 1997;
Driscoll, 1998; McGuigan et al., 1998). Some studies revealed possible deleterious effects of
removing several toes in amphibians (Clarke, 1972; Humphries, 1979; Golay & Durrer, 1994;
Reaser & Dexter, 1996) while others did not (Lemckert, 1996; Williamson & Bull, 1996;
Parris & McCarthy, 2001). Nonetheless, it is recognized that the removal of one toe is likely
not to provoke any negative effect on survival (McCarthy & Parris, 2004). In the present
34
study only a portion of one toe (2-3 mm) was removed and no adverse effects were observed
after release. The sample was stored for some weeks in the 1.5 ml screw cap plastic tubes
filled with 96% ethanol. The preservation of tissue for DNA extraction in ethanol for a short
time is appropriate because ethanol inhibits the proteolytic enzymes responsible for tissue
degradation. Once in the laboratory, the samples were stored in the fridge for few days until
DNA extraction. The DNA was extracted in the genetic laboratory of the Institute of Zoology
at the TiHO (co-responsible Prof. Dr. Heike Pröhl) in Hannover and at the Department of
Zoology of Cambridge University (evolutionary genetics group, responsible Dr. Nicholas
Mundy) using a Qiagen DNeasy extraction kits and a Qiagen QIAquick purification kit
respectively (Qiagen, Hilden, Germany) following the manufacturer's instructions. The
general procedure involved digestion of the tissue in 1.5 ml tubes containing a proteinase K
solution and incubation at 37°C overnight. The proteinase K releases the DNA from the tissue
and inhibits the nucleases enzymes responsible for nucleic acid degradation. Then a binding
buffer was added and the samples were passed through filtering mini-columns embedded in
1.5 ml centrifuge tubes. After centrifugation, a washing buffer was added to the columns to
eliminate the impurities from the filter that binds the DNA and the flow-through discarded. As
a final step the DNA was eluted by adding an elution buffer in two successive aliquots each
followed by centrifugation. The eluate was stored at -20° C. Small known aliquots of purified
DNA mixed with a loading dye were run on 1% agarose gel stained with ethidium bromide to
quantify the DNA yield and prepare proper dilution for subsequent amplification steps.
2.3 Phylogeography
2.3.1 Mitochondrial DNA sequencing
Two fragments of mitochondrial DNA were considered for the phylogeographic analysis. I
amplified a 600 bp fragment of the cytochrome b gene (cyt b) from 28 individuals (10
35
populations) using primers MTAL (Hauswaldt et al., 2011) and cyt b-c (Bossuyt &
Milinkovitch, 2000). A portion (527 bp) of the 16S rRNA gene (16S) was amplified in a
subset of samples (N = 16; 9 population) using universal primers 16SA and 16SB (Palumbi et
al., 1991) (Table 1). PCRs were performed in 25 µl volume using Taq DNA-polymerase
(Eppendorf, Hamburg, Germany). The thermocycling conditions for cyt b comprised an initial
denaturation at 95°C for 2 min followed by 35 cycles of denaturation (95°C for 45s),
annealing (52°C for 45s), elongation (72°C for 1min), and a final elongation at 72°C for 10
min. The profile for 16S was identical except for an annealing temperature of 55°C. PCR
products were purified using Qiagen purification kits and filtering columns system described
above. The purified PCR product was then precipitated and prepared for sequencing
according to standard procedure. The fragments were sequenced in both directions in 10 µl
volume using BigDye 3.1. The sequences were run on an ABI sequencer 3500 (Applied
Biosystems, Darmstadt, Germany).
2.3.2 Mitochondrial DNA analyses
Sequences were aligned and edited with MEGA 4.1 (Tamura et al., 2007). Haplotypes were
extracted using the on–line tool “DNA to haplotype collapser and converter” available in
FABOX 1.40 (http://www.birc.au.dk/software/fabox/). I calculated the number of variable
sites as well as uncorrected pairwise distances between populations (p-distance) using MEGA
4.1. I performed Maximum Likelihood and Bayesian phylogenetic analyses with PAUP* 4.0
(Swofford, 2002) and MrBayes 3.1 (Ronquist & Huelsenbeck, 2003), respectively. All the cyt
b sequences of comparable size published for O. granulifera were included in the analyses
(Wang, 2011; see Additional Information for all accession numbers). The populations
considered in Wang (2011) were Corcovado (CO), Drake Bay (DB), Piedras Blancas (PB),
Rio Terribe (TE), Rio Baru (RB), Cerro Nara (CN), Rio Savegre (SV), Rio Damitas (DM) and
Fila Chonta (FC). The geographical areas of Costa Rica where the populations were found
36
and the correspondent colour phenotypes described in Wang (2011) were: south-west, red
(CO, DB, PB), central-south-west, red (TE), central-west, red (BR), central-north, yellow
(CN, SV), central-north, green (DM, FC) (Fig. 1). Hereafter, these populations will be cited in
the text using the abbreviations. I am not aware of any sampled population in common with
Wang (2011) (Fig. 1). As outgroups, I included eight 16S sequences from all but one of the
other species of the genus Oophaga (nomenclatural authorities) [O. arborea (Myers et al.,
1984), O. histrionica (Berthold, 1845), O. lehmanni (Myers & Daly, 1976), O. pumilio, O.
speciosa (Schmidt, 1857), O. sylvatica (Funkhouser, 1956) and O. vicentei (Jungfer et al.,
1996); two sequences for O. pumilio northern and southern lineages, one sequence for each
other species; O. occultator (Myers & Daly, 1976) was not included because there were no
sequences available], two 16S sequences of Dendrobates leucomelas and D. tinctorius and
two cyt b sequences of O. histrionica and O. sylvatica, (see Additional Information for all
accession numbers). For ML analyses, I selected the model of evolution that best fitted the
data using jMODELTEST 0.1 (Posada, 2008). Analyses were carried out using a heuristic
search with 10 random additions per replicate and TBR branch swapping. Node confidence
was assessed using 1000 bootstrap replicates. Bayesian posterior probabilities were calculated
using MrBayes 3.1 (MCMC sampling) applying the substitution model selected in
MrModeltest 3.7. Two markov chains were run from random trees for 4 × 106 generations and
monitored to ensure that the average standard deviation of split frequencies was <0.01. The
20% of the initial trees were discarded as burn-in. Finally, I reconstructed the cyt b haplotype
network using TCS 1.21 (Clement et al., 2000) and determined the minimum number of
mutational steps required to connect different clusters of haplotypes using the fix connection
limit option. I included the same published cyt b sequences (Wang, 2011) considered in the
phylogenetic analyses.
37
2.4 Population genetics
2.4.1 Microsatellite loci genotyping and analyses
Seven microsatellite loci [B9, C3, D4, E3, F1, G5, O1] previously isolated for O. pumilio
(Hauswaldt et al., 2009) were amplified via PCR from seven to 15 individuals belonging to
eleven populations. PCRs were performed in 25 µl volume using Taq DNA-polymerase
(Eppendorf, Hamburg, Germany). The thermocycling conditions comprised an initial
denaturation step at 95°C for 30 sec followed by 35 cycles of denaturation (95°C for 30 sec),
annealing [48°C (C3); 57°C (B9, D4, F1); 59°C (E3); 60°C (G5); 64°C (O1) for 45 sec] and
elongation (72°C for 45 sec) followed by a final elongation at 72°C for 10 min. Then
genotyping (electrophoresis) was performed on a ABI 3500 sequencer (GE Healthcare, Little
Chalfont, UK) using ladder GeneRuler 100bp Plus (Fermentas, Vilnius, Lithuania) and
fragments were scored with GeneMapper 4.1 software (Applied Biosystem, Foster City,
California, USA). I used GenAlEx 6.4 (Peakall & Smouse, 2006) to calculate observed and
expected heterozigosities (Ho and He) and the number of private alleles (AP). Average allelic
richness (AR), for at least seven individuals per population was calculated with FSTAT
(Goudet, 1995). I tested each locus and population for linkage disequilibrium and deviation
from Hardy-Weinberg equilibrium (HWE) with Genepop on the Web (Fisher’s exact tests,
Raymond & Rousset, 1995a,b; Rousset, 2008) using the Markov chain Monte Carlo (MCMC)
and default parameters (10,000 dememorizations, 1000 batches and 10,000 iterations per
batch). FST pair-wise values (Weir & Cockerham, 1984) and the molecular variance
(AMOVA; Excoffier et al., 1992) were computed with Arlequin 3.11 (Excoffier et al., 2005).
Significance was tested with 10,000 permutations. Finally, I performed a population
assignment test based on Bayesian posterior probabilities as implemented in Structure 2.3.3
(Pritchard et al., 2000). Runs were performed with 1×106 burn-in period and MCMC of
3×106, setting an admixture model (αinitial = 1.0; αmax = 10.0). I tested one to 13 possible
clusters (K), and 10 runs were conducted for each K. The uppermost hierarchical level of
38
population structure was determined according to Evanno et al. (2005), checking the greatest
rate of change in estimated likelihood between successive K-values.
2.5 Colour description and measurements
For colour description, 189 frogs were photographed with a digital camera Nikon Coolpix
4500 and colour phenotype characteristics recorded from 11 populations distributed across the
known distribution range of O. granulifera (Table 1; Fig. 1). Light reflectance measurements
were taken from 15 individuals each from populations Firestone, Dominical, Matapalo,
Portalon and Savegre using an Ocean Optics 2000+ (Ocean Optics Inc., Dunedin, FL, USA)
fiber optic spectrometer and a deuterium-tungsten DT-Mini-2-GS light source. Reflectance
spectra were obtained averaging five measurements each from the head, upper dorsum and
lower dorsum. Geographical coordinates and localities altitudes were documented with a
Garmin GPS 12 (Garmin Ltd., Schaffhausen, Switzerland).
2.6 Bioacoustics
Male advertisement calls were recorded using a Sennheiser directional microphone (MHK
416 P48; Sennheiser, Wedemark-Wennebostel, Germany) and a digital walkman Marantz
(PMD 671, Marantz Corporation, Kanagawa, Japan). The calls of 59 frogs from nine
populations were recorded (Table 1). Due to very low calling activity in the Dominical and
Damitas populations, the calls of frogs from these populations could not be recorded. In most
populations the frogs were found in close proximity to creeks, therefore many of the recorded
calls contained background noise, leading to low sample size in some populations. During
recording the distance to the frogs was no more than two metres to minimize environmental
noise interference. The calls were recorded mostly in the morning hours (5.00 to 13.00) when
the calling activity was more intense. After each recording, air temperature was measured to
39
allow analyses to be controlled for temperature effect on the calls. Pulse rate, call duration and
call rate were calculated using oscillograms. Dominant frequency was measured by using
spectrograms. For details on call parameters definition see Pröhl (2003). Bioacoustic analyses
were performed using Avisoft (Avisoft Bioacoustics, Berlin, Germany). I used one-way
ANOVA to test for differences in call parameters among populations and colour morphs.
2.7 Morphology
Morphological measurements were collected from 147 frogs belonging to nine populations
(Table 1). Body weight was measured using a digital scale to the nearest 0.01g. Body (snoutvent), femor, tibia, humerus, radio-ulna and head lengths, head width, tympanum diameter
and between-nostril distance were measured with a digital calliper to the nearest 0.01mm. I
collected all measurements personally to avoid inter-operator variation. I used one-way
ANOVA to test for differences in morphological parameters among populations and colour
morphs.
40
3. Results
3.1 Colouration
I present the results on coloration first because they are important for interpreting the genetic
results. I found that the red colour phenotype gradually changed from the south (Charcos,
Neotropica, Ventana) to the north of the species distribution. I observed an increase in the size
of red patch over the body (Palmar, Firestone, Dominical, Baru) and then a change to an olive
green phenotype. In the transition area, populations were polymorphic and the two main
colour morphs (red and green) co-occurred with an array of intermediate phenotypes (Fig. 2,
3). The intermediate phenotypes were found together with the red morph in Matapalo and
with the green morph in Portalon and Savegre. The polymorphic populations occupy a
remarkably small area of approximately five Km while the whole sampled area was
approximately 110 km long. The southern (red) Charcos, Neotropica, and Ventana were all
located in the Osa peninsula and showed a similar colour pattern with a bright red dorsal
patch beginning at the head and covering 2/3 of the dorsum. The remaining body parts were
covered by a pale blue colour (Fig. 3a). In these three populations 57%, 33%, 55% of frogs
respectively had small red patches on the arms. The colour of the ventrum and limbs varied
from dark to pale blue with black reticulation often present on the dorsal surface and flanks,
but rarely on the ventrum. In Palmar, the frogs were almost completely red on the dorsum and
also usually had extended red patches on the arms and red spots on the proximal portion of the
legs (Fig. 3b). The red phenotype in Firestone was mainly dark red (75%) with less orange
individuals (25%), in Dominical the frogs were mainly orange (70%) while a minority was
red (30%) (Fig. 3c,d,e). In Baru I observed a uniform dark red colour. In Firestone and Baru,
54% and 33% of frogs had red spots on the ventral surface. In Dominical, in all frogs the
entire trunk was red or orange, including in some cases hands and feet and most of the
41
ventrum (33% of frogs). The rest of the ventrum and legs was azure (Firestone, Baru) to azure
grey (Dominical). In the populations Matapalo, Portalon and Savegre we found previously
undescribed colour phenotypes. In Matapalo, brightly red frogs (three out of 20) were found
to coexist with uniformly orange-green individuals (17 out of 20). The intermediate frogs in
this population showed different degrees of saturation, being either darker or lighter (Fig. 3
f,g). In Portalon, I observed highly variable intermediate colour phenotypes (50% of the
frogs) ranging from green with brown patches to red-brown and orange similar to those
identified in Matapalo. Also frogs with three concentric areas of different colour (brown,
yellow and green) were observed. The other half of the observed individuals displayed the
green phenotype (Fig. 3l). In Savegre, more uniform orange to gold-yellow intermediate
phenotypes (25%) were found. In this population, the green morph was most common (75%
of frogs) (Fig. 3i). In Damitas I found mostly green frogs, although four out of 13 individuals
showed a brown patch on the head smaller than the patches observed in Matapalo, Portalon
and Savegre. The ventrum and leg regions ranged from azure to green–azure (Fig. 2l). A
northern green population, not included in the present study, was located near the city of
Parrita outside the known distribution of O. granulifera. Moreover, the altitudal range
occupied by the species is wider than reported (20-100m asl; Savage, 2002; IUCN Red List of
Threatened Species), with populations (Baru, Matapalo, Portalon, Savegre) extending up to
400m asl. The reflectance spectra confirmed the colour intergradation among Firestone and
Dominical. The spectra from Matapalo, Portalon and Savegre showed the presence of a
gradual variation from green to orange (Fig. 4). The colour variation in O. granulifera can be
broadly categorised in the following chromatic areas: red (red), orange (intermediate), orangegreen (intermediate), green-yellow-brown (intermediate), green-brown (intermediate) and
green (green) (Table 2).
42
Table 2 Grouping of O. granulifera colour phenotypes into six categories. Symbols describe
the colour variation occurring in the populations as follow: Red (■), Orange (□), Orangegreen (◙), Green-yellow-brown (◘), Green-brown (○), Green (●).
Population
Colour
Charcos
■
Neotropica
■
Ventana
■
Palmar
■
Firestone
■□
Baru
■
Dominical
■□
Matapalo
■◙
Portalon
◙◘○●
Savegre
◙◘○●
Damitas
○●
43
Figure 2 Sampling localities of Oophaga granulifera. The pie-graphs indicate the proportion
of red, intermediate and green phenotypes in each of the populations sampled for the present
study. The populations from Wang (2011) are marked with *. Population codes as in Table 1.
44
Figure 3 Dorsal colour variation in Oophaga granulifera. (a) Osa peninsula [■], (b) Palmar
[■], (c) Firestone [■], (d) Firestone [□] , (e) Dominical [□], (f,g) Matapalo [◙] , (h)
Portalon [◙] , (i) Savegre [○], (l) Damitas [●]. In [ ] colour symbols as in Table 2.
Photographs by Oscar Brusa
45
Figure 4 Average reflectance spectra of O. granulifera from populations (a) Firestone, (b)
Dominical, (c) Matapalo, (d) Portalon, (e) Savegre.
46
3.2 Mitochondrial DNA variation and divergence
There were 17 variable sites and five haplotypes identified in 16S (N = 16) and 44 variable
sites and twelve haplotypes identified in cyt b (N = 30). Both markers identified a southern
(Osa peninsula) and a northern (all remaining populations) genetic lineages. For 16S, the
average genetic distance between the population Charcos (Osa peninsula) and all the other
populations was 1.9% (Table 3). The distances for 16S among the other seven Oophaga spp.
included in the analyses varied between 0.8% and 3.2% with a mean of 1.9%. The average
distance between O. granulifera and the other Oophaga spp. was 5.5%, while the average
distance between Oophaga spp. and the species D. leucomelas and D. tinctorius was 9.2%
and 11.5% respectively (Table 3). Interpopulation genetic distances (p-distance) for cyt b
varied from 0.0 to 4.3% (Table 4). The average genetic difference between southern and
northern populations for the same marker was 4%, while the divergence among the northern
populations varied from 0.1% to 0.8% (Table 4). In the northern lineage, the average genetic
distance between Palmar and the other populations (0.8%) was higher than among the latter
(0.2%). From the AMOVA, most of the variation was among lineages (91.65%, Φct = 0.92, P
< 0.001), whereas variation within populations (3.75%, Φst = 0.97, P < 0.001) and within
southern and northern lineages (4.60%, Φsc = 0.55, P < 0.001) were much lower.
47
Table 3 16S sequence divergence (uncorrected p-distances) between the two lineages of Oophaga granulifera,
seven other Oophaga spp. and two Dendrobates spp. “O.gran. south” indicates the O. granulifera southern
lineage; “O.gran. n” indicates the O. granulifera northern lineage.
Species
D.leu
D.tin
O.arb
O.his
O.leh
O.pum
O.spe
O.syl
O.vic
O.g. S
D.leucomelas
D.tinctorius
0.062
O.arborea
0.085
0.106
O.histrionica
0.094
0.115
0.008
O.lehmanni
0.092
0.110
0.014
0.014
O.pumilio
0.096
0.119
0.020
0.028
0.030
O.speciosa
0.092
0.108
0.014
0.018
0.020
0.026
O.sylvatica
0.092
0.110
0.012
0.016
0.014
0.032
0.022
O.vicentei
0.096
0.110
0.016
0.018
0.020
0.024
0.018
0.024
O.gran. S
0.109
0.133
0.048
0.054
0.049
0.065
0.059
0.050
0.055
O.gran. N
0.106
0.124
0.049
0.053
0.053
0.070
0.064
0.051
0.059
0.019
Table 4 Cyt b sequence divergence (uncorrected p-distances) among the investigated populations of Oophaga
granulifera. Populations abbreviated as in Table 1.
Population
CH
VE
PA
FS
DO
BA
MA
PL
SA
Charcos
Ventana
0.004
Palmar
0.036
0.035
Firestone
0.040
0.041
0.007
Dominical
0.041
0.042
0.008
0.001
Baru
0.042
0.043
0.009
0.004
0.005
Matapalo
0.040
0.041
0.007
0.001
0.002
0.004
Portalon
0.042
0.042
0.009
0.002
0.001
0.006
0.003
Savegre
0.041
0.042
0.008
0.001
0.000
0.005
0.002
0.001
Damitas
0.041
0.042
0.008
0.001
0.000
0.005
0.002
0.001
0.000
48
3.3 Mitochondrial DNA phylogeography and population structure
Maximum-likelihood (ML) and Bayesian analyses revealed a deep genetic separation of the
southern populations, Charcos and Ventana, from all the other populations for both
mitochondrial markers (Fig. 5). The phylogeny reconstructed with 16S sequences indicated a
clear differentiation between the two lineages of southern and northern O. granulifera with
100% node support for both ML and Bayesian trees. I also found a higher level of divergence
of the species compared with the other Oophaga spp. (Fig. 5a). Similarly, in the cyt b tree the
node separating the Osa peninsula from the other populations was highly supported by
bootstrap and posterior probability values (ML = 98, BI = 1.00, Fig. 5b). The cyt b tree also
showed moderate support for a derived monophyletic clade including Firestone, Dominical,
Baru, Matapalo, Portalon, Savegre and Damitas populations. Within this clade, the divergence
of two haplotypes from Baru and two from BR was supported by significant values of
bootstrap and posterior probability (ML = 86, BI = 0.99, Fig. 5b). Despite a moderately
supported divergence from the other northern populations, Palmar was included in the
northern lineage (Fig. 5b). The haplotype network (cyt b) confirmed the genetic separation of
the populations located south and north of the river Río Térraba (Fig. 6), with the two clusters
being separated by a minimum of 20 mutational steps. Eleven out of 16 haplotypes (seven in
the northern and four in the southern lineage) were private. Within the northern lineage,
haplotypes are shared among intermediate and monomorphic red or green populations except
for haplotypes H11 and H12 belonging to Portalon and Matapalo respectively (Fig. 6).
49
Figure 5 Phylogenies obtained analysing (a) 16S and (b) cyt b sequences. The ML bootstrap
values and Bayesian posterior probabilities are reported at nodes. For each O. granulifera
sequence we indicated: the species name, the population code (as in Table 1) and sample
number and in (b) the haplotype code (H1 to H16); “Wang” indicates the sequences from
Wang (2011) included in the analyses; font colours correspond to O. granulifera colour
morphs as follows: red = red morph, yellow = intermediate morphs, green = green morph. S =
southern lineage, N = northern lineage. * indicates sequences from Palmar, ** indicate
sequences from TE.
(a)
(b)
50
Figure 6 Network of cyt b haplotypes of Oophaga granulifera. Haplotypes (H) are indicated
by circles whose areas correspond to the haplotype frequency; S and N indicate southern and
northern lineages; the dashed double arrow shows the minimum separation between lineages.
Correspondences between colours and populations are indicated in figure; * distinguishes the
populations sampled for this study (coded as in Table 1) from the populations sampled in
Wang (2011) included in the analyses (Fig. 1).
51
3.4. Microsatellite loci population structure
All microsatellite loci except one were polymorphic for the eleven O. granulifera populations.
Locus D4 was monomorphic in the three populations sampled south of the river Río Térraba
(Charcos, Ventana and Neotropica). No deviation in linkage disequilibrium was found (P >
0.05). In eight populations one to two loci deviated from HWE after Bonferroni correction
(Table 5). Within-population diversity was overall higher in southern populations than in
northern ones (Table 5). Allelic richness ranged from 5.11 (± 2.00) in Matapalo to 8.00 (±
3.27) in Ventana and was higher in the southern populations and Palmar (6.97 on average)
than in the northern populations (5.12). Private alleles were mainly found in the three
southern populations, Charcos, Ventana and Neotropica, as well as in Palmar sampled just
north of the river Terraba (9.5 on average), while they were scarce in other northern
populations (2.3 on average). Significant FST values (P < 0.05) were detected in 52 out of 55
pairwise comparisons among populations (Table 6). Mean FST value was 0.11 (± 0.05),
ranging from 0.01 (between Baru and Firestone) to 0.18 (between southern population
Charcos and the northernmost green population Damitas). Population of the northern mtDNA
lineage had higher average FST value (0.11 ± 0.05) than those belonging to the southern
lineage (0.05 ± 0.01). AMOVA results markedly differed from those with the mitochondrial
cyt b marker. Most of the variation was found within populations (84.53%, FST = 0.15, P <
0.01), whereas variation among lineages (9.63%, FCT = 0.10, P < 0.001) and among
population within lineages (5.84% FSC = 0.06, P < 0.001) were much lower. Bayesian
assignment analysis identified two well defined clusters (Fig. 7; see Additional Information
for ∆K results). The first one included the Osa Peninsula populations, while the second
grouped all the populations belonging to the northern mitochondrial lineage except Palmar.
Palmar presented an intermediate population structure having genotypes similar to both the
southern and the northern clusters (Fig. 7). The differentiation of Palmar from Charcos,
Neotropica, Ventana grouped in the southern cluster is confirmed by high pairwise Fst values
52
(Table 6). One individual from the northern population Dominical showed a genetic profile
close to the southern populations. Admixture was high within the clusters and low among
clusters (Fig. 7).
Table 5 Analyses of seven microsatellite loci of Oophaga granulifera; n = number of
individuals analysed; AR[14], mean allelic richness (± SD) estimated for a minimum of seven
individuals; Ho, observed heterozygosity (± SD); He, expected heterozygosity (± SD); HWE,
loci out of Hardy–Weinberg equilibrium after Bonferroni correction; AP, number of private
alleles.
Population
Charcos
Neotropica
Ventana
Palmar
Firestone
Dominical
Baru
Matapalo
Portalon
Savegre
Damitas
n
8
8
7
7
8
8
8
10
15
8
11
AR[14]
6.95 ± 3.07
6.62 ± 3.15
8.00 ± 3.27
6.29 ± 2.75
4.92 ± 2.06
5.12 ± 1.75
4.83 ± 1.25
5.11 ± 1.99
5.36 ± 2.15
5.40 ± 2.17
5.24 ± 2.76
Ho
0.71 ± 0.42
0.75 ± 0.37
0.71 ± 0.35
0.55 ± 0.21
0.66 ± 0.21
0.61 ± 0.15
0.61 ± 0.25
0.70 ± 0.23
0.69 ± 0.18
0.71 ± 0.20
0.64 ± 0.29
He
0.72 ± 0.32
0.71 ± 0.32
0.73 ± 0.32
0.73 ± 0.14
0.66 ± 0.16
0.67 ± 0.13
0.66 ± 0.16
0.65 ± 0.19
0.73 ± 0.14
0.68 ± 0.15
0.67 ± 0.24
HWE
D4, G5
D4, G5
D4
O1
F1
O1
O1
C3
AP
6
8
15
9
1
2
–
3
1
–
1
Table 6 Differentiation between Oophaga granulifera populations estimated by pairwise FST
values. (*) Significant FST values (P < 0.05). Population codes (Pop) as in Table 1.
Pop
CH
NE
VE
PA
FS
DO
BA
MA
PL
SA
DA
CH
–
0.05*
0.04*
0.14*
0.17*
0.15*
0.15*
0.17*
0.13*
0.14*
0.18*
NE
VE
PA
FS
DO
BA
MA
PL
SA
DA
–
0.06*
0.16*
0.16*
0.16*
0.13*
0.17*
0.12*
0.12*
0.16*
–
0.13*
0.16*
0.14*
0.15*
0.17*
0.14*
0.12*
0.18*
–
0.11*
0.14*
0.10*
0.13*
0.11*
0.07*
0.11*
–
0.10*
0.01
0.07*
0.07*
0.05*
0.06*
–
0.09*
0.11*
0.04*
0.06*
0.08*
–
0.07*
0.05*
0.03
0.06*
–
0.04*
0.06*
0.06*
–
0.03*
0.05*
–
0.02
–
53
Figure 7 Assignment probabilities of individuals of Oophaga granulifera from Costa Rica to
putative population clusters at K=2 using the program STRUCTURE. Populations codes (as
in Table 1, font colours as in Fig.5).
3.5 Bioacoustics
Call duration, call rate and dominant frequency were significantly different between southern
and northern lineages, whereas there was no difference in pulse rate (Table 7). In the southern
genetic lineage frogs had longer and slower calls and higher dominant frequency as compared
to the northern lineage (Table 8; Fig. 8). Variability among populations was highest for call
duration while it was lowest for dominant frequency (Table 9). The calls of Charcos,
Neotropica and Firestone showed the lowest variation. The calls of the males from Portalon
and Savegre were the most variable (Table 9). Within the northern lineage, pulse rate
significantly differed between the red and green colour morphs (F = 10.16, P < 0.001).
54
Table 7 ANOVA results testing for differences in call parameters between southern and
northern populations of Oophaga granulifera. Abbreviations for call parameters: PR = pulse
rate, CD = call duration, CR = call rate, DF = dominant frequency. * indicates significant
values.
Variable
F
P
PR (1s–1)
3.14
0.082
CD (s)
70.11
<0.0001*
CR (1s–1)
6.36
0.015*
DF (kHz)
6.36
<0.0001*
Table 8 Male advertisement call parameters in the Oophaga granulifera populations. N =
number of individuals recorded. Abbreviations for call parameters: PR = pulse rate, CD = call
duration, CR = call rate, DF = dominant frequency. All values given as mean ± SD.
Population
N
PR (1s–1)
CD (s)
CR (1s–1)
DF( kHz)
Charcos
9
174.14±17.06
0.53±0.08
10.37±0.95
4.21±0.19
Neotropica
14
165.99±14.97
0.57±0.08
9.93±1.21
4.20±0.15
Ventana
7
203.59±36.38
0.44±0.10
11.70±1.83
4.32±0.16
Palmar
3
168.76±26.73
0.28±0.07
16.85±2.07
4.07±0.28
Firestone
4
172.49±18.74
0.33±0.03
14.60±1.40
4.15±0.08
Baru
4
181.51±22.85
0.31±0.1
16.33±2.12
4.16±0.18
Matapalo
3
209.13±49.36
0.36±0.09
15.75±2.36
3.97±0.11
Portalon
3
211.37±24.16
0.26±0.11
17.67±2.03
3.98±0.22
Savegre
5
221.98±33.71
0.32±0.13
14.27±1.80
4.27±0.06
55
Figure 8 Variation in male advertisement call parameters among southern and northern
populations of Oophaga granulifera: (A) call duration ; (b) call rate; (c) dominant frequency;
(d) pulse rate
(A)
(B)
56
(C)
(D)
57
Table 9 Coefficients of variation [(mean/standard deviation)*100] for the male advertisement
call parameters. µpop = mean across populations. Abbreviations for call parameters: PR =
pulse rate, CD = call duration, CR = call rate, DF = dominant frequency.
CVPR
CVCD CVCR
CVDF µpop
Charcos
9.8
14.5
9.1
4.6
9.6
Neotropica
9.0
13.5
12.2
3.7
9.4
Ventana
17.9
23.2
15.6
3.6
14.6
Palmar
15.8
24.3
12.3
6.9
15.1
Firestone
10.9
7.9
9.6
1.8
7.9
Baru
12.6
31.9
13.0
4.3
16.1
Matapalo
23.6
24.2
15.0
2.9
15.7
Portalon
11.4
41.5
11.5
5.5
19.7
Savegre
15.2
40.6
12.6
1.3
19.9
µpar
14.0
24.6
12.3
3.8
16.3
3.6 Morphology
The parameters weight, body length, femur length, tibia length, humerus length and radioulna length significantly differed between southern and northern genetic lineages (Table 10;
Fig. 9). Frogs belonging to the red southern populations were lighter, smaller and with shorter
limbs than frogs from red, intermediate and green northern populations. Among the northern
populations, head length (F = 7.99; P < 0.0001), head width (F = 24.74; P < 0.0001),
tympanum diameter (F = 9.68; P < 0.0001) and between-nostril distance (F = 6.98; P <
0.0001) together with body weight (F = 15.57; P < 0.0001) and body length (F = 9.34; P <
58
0.0001) were significantly different between red and green colour morphs. In the northern
lineage, red frogs were heavier, longer and had an overall larger head compared to the green
ones.
Table 10 ANOVA comparisons between genetic lineages for ten morphological parameters. *
indicates significant values
Variable
F
P
weight
F= 21.66
P < 0.0001*
body length
F = 20.45
P < 0.0001*
femur length
F = 28.61
P < 0.0001*
tibia length
F = 66.75
P < 0.0001*
humerus length
F= 7.15
P < 0.0001*
Radio-ulna
length
F= 0.42
P < 0.0001*
head length
F= 0.13
P = 0.71
head width
F = 1.19
P = 0.28
tympanum
diameter
F=0.253
P = 0.14
Between-nostril
distance
F = 0.33
P = 0.56
59
Figure 9 Box plots for ten morphological variables comparing southern and northern genetic
lineages in O. granulifera. (A) body weight, (B) body (snout-vent) length, (C) tibia, (D)
femor, (E) humerus, (F) radio-ulna, (G) head-width, (H) head length, (I) tympanum diameter,
(L) between nostril-distance.
(A)
60
(B)
(C)
61
(D)
(E)
62
(F)
(G)
63
(H)
(I)
64
(L)
65
4. Discussion
4.1 General discussion
The fine-scale analysis of genetic and phenotypic variation conducted in the present study
revealed significant geographical divergence in genetics, colouration, advertisement calls and
body size, in Oophaga granulifera populations in Costa Rica. Specifically, the results here
presented show that O. granulifera possesses higher colour diversity than previously
described (Savage, 2002; Wang, 2011). Beside the red, yellow and green colour morphs, the
species shows an array of intermediate morphs and is polymorphic in the northern part of its
distribution. Most of this remarkable variation occurs in a small transition area between
populations monomorphic for red and green phenotypes. To the north of the river Río
Térraba, first the colour phenotype changes quantitatively following a well defined southnorth cline toward increase of the red body area. Then the colour phenotype differentiates into
an array of colours spanning the chromatic range between red and green. In contrast, all
populations occurring in the Osa peninsula in the south of the distribution are very consistent
in colour characteristics. I provide the first description of colour polymorphic populations of
O. granulifera. The three polymorphic populations consisted of yellow morphs together with
green or red and other novel intermediate phenotypes. Thus, in contrast to previous studies
(Savage, 2002; Wang, 2011), intermediate frogs were always found in polymorphic
populations. The distribution of colour morphs in O. granulifera is asymmetric compared to
the genetic structure resulting from the phylogenetic reconstruction. The southern lineage is
monomorphic red while the northern lineage contains red, green and polymorphic
populations. Within the northern lineage, a monophyletic clade includes all of the northern
populations except Palmar. In this clade, Firestone, Dominical, Portalon, Matapalo, Savegre
and Damitas are closely related while Baru appears to be more differentiated. In contrast to a
66
previous study (Wang, 2011), I did not find a monophyletic yellow-green clade, which
presumably relates to the more comprehensive sampling in the colour transition area
performed in the present study. A missing link between colour and genetic differentiation in
poison frogs has been previously observed in O. pumilio (Hagemann & Pröhl, 2007; Wang &
Shaffer, 2008; Brown et al., 2010; Hauswaldt et al, 2011; but see Wang & Summers, 2010).
A recent colour radiation might explain the lack of correspondence between genetic
divergence at mitochondrial loci and colour divergence. According to our phylogeny the
Palmar population belongs to the northern lineage while the TE population from Wang (2011)
belongs to the southern one. Interestingly, the sample location was north of the river Río
Térraba while Wang (2011) sampled south of it (Ian Wang, pers. comm.; in the cited study the
name of the river was misspelled as Rio Terribe). The River Río Térraba is the largest of
Costa Rica and has been estimated to have originated in the Quaternary period (Bergoeing, et
al., 1997). The historical presence of such an important physical barrier may well present the
major determinant of the observed inter-lineage divergence. Considering a mutation rate for
mitochondrial DNA of approximately 2% per million years (Avise, 2000), the genetic
distance I observed between lineages (4% for cyt b) is congruent with a role of the river Río
Térraba in the O. granulifera intra-specific divergence. The analyses of 16S data confirms the
divergence between the southern and northern lineages and show that the intraspecific genetic
distance in O. granulifera is comparable to the distance between different Oophaga species.
The data therefore show, using a much larger sampling than previous studies (nine
populations instead of one), that O. granulifera is highly divergent from all congeneric
species (Hagemann & Pröhl; Summers & Clough, 2000). The divergence into two main
lineages is furthermore supported by the haplotype network that defines two clusters
corresponding to the southern and northern lineages. Deep intraspecific genetic divergence
has been found in other dendrobatids. For instance, high divergence in cyt b haplotypes is
reported for Epipedobates femoralis and E. hahneli from Western Amazonia (12% and 7.1%,
67
Lougheed et al., 1999; Roberts et al., 2007), and in O. pumilio from Costa Rica and Panama
(7%, Hauswaldt et al., 2011). Nonetheless, the present study is the first providing concordant
lines of evidence for a deep inter-specific divergence, using historical and recent genetic
inference and phenotypic traits. Notably, the two O. granulifera lineages diverged both in
advertisement calls and in morphological traits and present highly reduced gene admixture.
The frogs of the Osa peninsula are smaller and have longer notes (calls), lower call rate and
higher dominant frequency. Thus, the two lineages have undergone divergent evolutionary
trajectories leading to a deep divergence in which reinforcement mechanisms, such as
assortative mating, were presumably involved in impeding hybridization. The opposite
geographical trend has been found in O. pumilio in Costa Rica, in which two southern and
northern genetic lineages roughly correspond to two bioacoustic groups, and the southern
frogs were bigger and had higher call rate (Pröhl et al., 2007; Hagemann & Pröhl, 2007;
Hauswaldt et al., 2011). This may be explained if stochastic genetic processes, linked for
example to demographic fluctuations during colonization movements, are important factors in
originating intraspecific divergence, secondarily maintained and increased by selection.
The microsatellite STRUCTURE analysis evidences the presence of two well distinguished
southern and northern genetic clusters corresponding to the mitochondrial lineages with the
exception of the population Palmar which has an intermediate genetic structure sharing
genotypes from both clusters (Fig. 7). This is likely to be dependent on the peculiar location
of this population which is in between the southern and the northern populations (Fig. 2). In
particular, the pattern may be explained considering the geographical proximity between the
populations occurring in the Río Térraba area (Palmar and TE) together with changes in the
water level and position of the river that may have occurred over time. Overall, the genetic
data show a deep intraspecific divergence between populations located south and north of the
river Río Térraba and indicate the populations of the river basin as historical link between the
two lineages. The differentiation I observed in both calls and morphology between red,
68
intermediate and green colour morphs points to a potential role of mate choice in Oophaga
granulifera colour divergence. Interestingly, in the colour transition area, the majority of the
intermediate phenotypes co-occur with the green phenotype (Portalon, Savegre).
Both genetic and colour geographical variations in O. granulifera do not follow a clear cline,
considering the admixture among populations within the northern cluster and the asymmetric
distribution of intermediate phenotypes in the colour transition area. The lack of a clear colour
cline and a genetically well defined hybrid area may be explained if some of the intermediate
colour phenotypes in O. granulifera are not hybrids between red and green morphs, but
evolutionary steps from the red to the green phenotype. This would explain the fact that we
did not observe any population where pure red and green morphs co-occur. The observed
pattern in colour variation may be the result of complex crossing between red, intermediates
and green morphs over time across the colour transition area.
Wang (2011) stated that the O. granulifera cryptic morph was derived from the bright red
morph. In my opinion Wang (2011) and our phylogeographic reconstruction are congruent
with both a direct evolution of the green morph from a red ancestor and an indirect evolution
via intermediate steps. The green morph might have evolved from the red one and all the
intermediate morphs found in the transition area would be the result of hybridization between
red and green morphs or, alternatively, the intermediate morphs evolved from the red and
subsequently diverged to the green morph. In the second case, the intermediate colours
observed in the transition area would be a mixture of pure phenotypes and hybrids. The
coexistence of bright and dull colour morphs we found in the O. granulifera northern lineage
was also observed in the O. pumilio southern lineage (Hagemann & Pröhl, 2007; Wang &
Shaffer, 2008; Hauswaldt et al., 2011). These colour phenotypes have different
conspicuousness against the natural background (Pröhl & Ostrowski, 2011; Wang, 2011),
supporting the hypothesis that aposematic and cryptic colour morphs can coexist in systems
primarily evolved as aposematic (Darst et al., 2006; Speed & Ruxton, 2007). Several
69
evolutionary factors have been considered to explain the puzzling colour divergence in poison
frogs: genetic drift, differential predation pressure, toxin availability and sexual selection
(Speed & Ruxton, 2007; Rudh et al., 2007; Summers et al., 1997, 1999; Saporito et al.,
2007a). Interestingly, I found that the polymorphic and green populations show reduced body
size. This is congruent with the evolution of a cryptic antipredator strategy based on lack of
detectability to the predator instead of conspicuous signalling (Hagman & Forsman, 2003). In
addition, the lower genetic variation in the northern populations as revealed by microsatellite
allele diversity points to a possible role of genetic drift in the evolution of colour divergence
in O. granulifera. The effect of stochastic variation on allele frequency was advanced to
explain the evolution of isolated populations (Wright, 1977, Nosil, 2007). Examples have
been reported in O. pumilio and Heliconius butterflies (Rudh et al., 2007; Mallet & Joron,
1999). The presence of highly variable gradual intermediate colour morphs in O. granulifera
and the high population admixture in the northern lineage suggest that a certain amount of
gene flow between colour morphs exists in the colour transition area. Consequently, the
colour divergence within the northern lineage implies the maintenance of selection. Femalebiased parental care as observed in the Oophaga group may have increased female choosiness
and created the conditions for sexual selection through assortative mating by visual and
acoustic cues (Summers et al., 1997). Since male vocalizations are key sexual signals in frogs,
the difference in the pulse rate of the male advertisement call we found between red and green
colour morphs suggest the potential occurrence of female mate choice. The divergence in
body size, may also suggest a role of sexual selection in intraspecific divergence in O.
granulifera. In fact, assortative mating mediated by body size is demonstrated in amphibians
(Berven, 1981; Gabor et al., 2000; Takahashi et al., 2010). Reduced body size may therefore
have originated by natural selection for increased crypsis and be maintained by differential
mating selection in the colour transition area. Empirical tests in the field using mate choice
70
experiments are required to evaluate the actual role of sexual selection in the evolution and
maintenance of colour diversity in O. granulifera.
4.2 Why should a cryptic morph evolve in an aposematic species?
4.2.1 General background
Colour pattern polymorphisms can arise and be maintained by selection favouring multiple
variants within populations (Hoffman & Blouin, 2000; Merilaita, 2006; Vercken et al., 2007;
Dijkstra et al., 2008). Nonetheless, an aposematic species is a peculiar case in which the
evolution of colour diversification is predicted to be highly constrained (Müller, 1879).
Particularly, the possible adaptive role of a cryptic colour variant in an aposematic system is
debated. In fact, this is in constrast with the aposematism theory which predicts the functional
association of toxicity and conspicuous colour to enhance the efficancy of the deterrent signal
to predators. In non toxic species, a cryptic colouration can facilitate predator avoidance
(Cott, 1940; Endler, 1992; Duellman, 2001) therefore being under natural selection
(Robertson, 2008) or can be involved in mate choice (Gomez & Thery, 2007). Laboratory
studies have tested predation rates as a function of colour pattern in polymorphic frogs and
found that predators attacked cryptic (background-matched) morphs less often (Tordoff, 1980;
Morey, 1990). However, for toxically defended anurans such as poison-arrow frogs, bold
colour patterns and overall conspicuousness are thought to protect individuals from predation
attempt and detrimental effects connected (Summers & Clough, 2001; Darst et al., 2006).
Disentangling the selective forces responsible for colour diversification in aposematic
dendrobatids is difficult because several different and potentially interacting processes could
underlie divergent phenotypic expression, including natural (Hairston, 1979; Endler, 1980)
and sexual selection (Endler, 1983; West-Eberhard, 1983; Panhuis et al., 2001; Masta &
71
Maddison, 2002; Maan et al., 2004). I discuss here those among these selective forces that are
considered the most significant and how these may apply to O. granulifera.
4.2.2 Role of genetic drift
Stochastic fluctuations in allelic frequencies have been proposed to play a role in the
evolution of animal populations (Wright, 1933). Recently the actual role of drift has been reevaluated and its potential evolutionary effects are not considered of general application.
Nonetheless, under particular conditions such as population reduction and isolation the effect
of drift may be significant and shaping the evolutionary trajectories taken by those
populations (Lande, 1977). This may be the case, for instance, for the colour diversity
observed in the Panamanian populations of O. pumilio, which are small and separated (Rudh
et al., 2007). In O. granulifera, population size reduction may have happened during the
colonization movements toward the northern part of the distribution. The data concerning
microsatellite allelic diversity here presented suggest a decrease in genetic diversity in the
northern intermediate and green populations, concordant with an effect of drift. Drift may
have, for example, determined fluctuations in the frequency of the red aposematic morph
creating the conditions for a colour diversification in combination with other factors. It is
interesting at this regard, considering that theoretical models predict an association between
the frequency of the aposematic morph in the population and the promptness with which
predators learn to avoid it (Speed, 1993; Turner & Speed, 1996; MacDougall & Dawkins,
1998; Servedio, 2000; Speed & Ruxton, 2007).
4.2.3 Role of predation
In aposematic toxic animals, it has been shown that conspicuousness, that is a highly
contrasted appearance to the background, can make individuals more vulnerable to attacks by
naïve (e.g., Lindström et al., 2001a,b; Riipi et al., 2001; Lindstedt et al., 2008) or specialized
72
predators (Yosef & Whitman, 1992). Moreover, the predators visual and learning abilities and
resistance to prey toxicity, may vary both within and among species determining locally
variable predation risk for a potential aposematic prey (Calvert, 1979; Fink & Brower, 1981;
Yosef & Whitman, 1992; Pinheiro, 1996; Mappes & Alatalo, 1997; Marples et al., 1998;
Exnerová et al., 2003, 2007). Another factor to take into consideration is the ecological
community to which the aposematic animals belong to. Also, the vulnerability to predation
depends on the amount of alternative prey available (Merilaita & Kaitala, 2002; Lindström et
al., 2004) and the hunger level of predators (Barnett et al., 2007; Sandre et al., 2010). Overall,
predation could select for intermediate signals in some circumstances (Endler & Mappes,
2004; Tullberg et al., 2005; Ruxton et al., 2009) or allow for signal variation in others (Rowe
et al., 2004; Darst et al., 2006; Ham et al., 2006; Ihalainen et al., 2007). Generally, predators
are thought to learn to avoid unpalatable prey faster if they are conspicuous rather than cryptic
(Gittleman & Harvey, 1980; Roper & Redston, 1987; Alatalo & Mappes, 1996; Lindström et
al., 1999b) and if they are clearly visible (highly contrasted) against their background (Roper
& Redston, 1987; Lindström et al., 1999b; Gamberale-Stille, 2001; Prudic et al., 2007). Many
typical warning colours (e.g. red, orange or yellow) may also be innately aversive to predators
in comparison with common cryptic colours, such as green and brown, which can increase the
benefits of being warning coloured (Smith, 1975; Schuler & Hesse, 1985). Despite the
advantages of clearly visible warning colours (Guilford, 1986; Gamberale-Stille, 2000;
Schlenoff, 1984; Marples et al., 1998; Thomas et al., 2003; Roper & Redston, 1987; Roper,
1990; and Sherratt & Beatty, 2003; Ham et al., 2006), intermediate warning signals may be
selected instead of conspicuous ones if the predation risk varies (Endler & Mappes, 2004). In
dendrobatids the importance of predation as a driving force in the evolution of colour
diversity has been recently evidenced using empirical tests to assess the actual association of
colour phenotype and predation pressure (Comeault & Noonan, 2011, Saporito et al., 2007b).
The efficacy of an aposematic defense is dependent on the frequency of the conspicuous
73
colour morph characterizing the system (Speed, 1993; Turner & Speed, 1996; MacDougall &
Dawkins, 1998; Servedio, 2000; Lindström et al., 2001b; Speed & Ruxton, 2007), because a
high frequency is necessary to elicit the avoidance learning by the predators increasing the
deterrent efficacy of the signal. In O. granulifera, as mentioned, a demographic reduction may
be related to a decrease in genetic variability in the northern green populations. This together
with a colonization movement south-north (Wang, 2011) point to possible demographic
fluctuations linked to the occupancy of new habitats. If, following genetic drift phenomena,
the frequency of the red morph decreased in the O. granulifera northern populations, an
increased predation pressure on the that conspicuous morph may have produce a positive
selection for a cryptic variant. Moreover, the less conspicuous behaviour observed in the
green morph (personal observation) is congruent with an overall cryptic strategy of the green
morphs in O. granulifera. Importantly, to allow a significant evaluation of the role of
predation in the evolution of colour diversity in dendrobatids, the actual level of toxicity of
cryptic and conspicuous morphs has to be taken into consideration (Maan & Cummings,
2012).
4.2.4 Role of toxicity
The presence of chemical defences is a fundamental trait of aposematic defences as the
predators learn to avoid a conspicuously colours animals due to the unpalatability and adverse
effect provoked by toxins (Muller, 1879). Therefore, the possible variation of the actual
toxicity in a population may influence the selection pressure at the local level and create
potential for the diversification in aposematic signals (Wang, 2011). It has been proposed that
once aposematism is established in a system, then colouration can become decoupled and
diversifies following local variation in toxicity. There is evidence that in O. pumilio, the dull
coloured less constrasted (cryptic) morphs are significantly less toxic than the bright coloured
morphs (Maan & Cummings, 2012). This finding is in contrast with Wang (2011) for O.
74
granulifera that showed an overall higher toxicity in green and intermediate morphs. These
two apparently contrasting findings may be explained considering a crucial point in
dendrobatid chemical defences that is the dependence on the diet as a source of toxins. In fact,
spatial and temporal variation in the prey communities from which dendrobatids derive their
alkaloids must be taken into consideration before depicting any related evolutionary scenario.
In the two mentioned studies these longterm observational data are missing therefore any
deduction has to be careful (see Saporito et al., 2007c). Another factor that has to be
thoroughly weighed is the methodology that has been followed up to date to evaluate the
toxicity of dendrobatids, which is an intradermal injection of frog skin extract in laboratory
mice. Both the species used and the way of assumption may not be optimal representation of
the real processes as they happen in nature. Nonetheless, the difference in toxicity was
quantitative (toxicity essays; both studies) and qualitative (number of identified alkaloids;
Wang, 2011) and is consistent across different cryptic morphs therefore it may represent an
important factor in the evolution of colour diversity in aposematic species. The possible
reason explaining the constrasting pattern observed in O. pumilio and O. granulifera may be
dependent on the different biogeographic conditions in which the two systems evolved.
Indeed, most of O. pumilio colour diversity is found in the Bocas del Toro archipelago in
Panama, formed by many different small islands of recent origin while O. granulifera is
found in mainland Costa Rica in a potentially continuous distribution. In O. granulifera, the
effect of an increased toxicity may have reduced the need for a bright colouration over time.
This is because, predators can learn to avoid a highly toxic not profitable prey even if dully
coloured. The related evolutionary mechanism is compatible with individual selection because
any predation attempt may be neutralized if powerful toxins cover the body surface, such as in
the case of dendrobatids, determining immediate repellent and noxious effects to the predator.
Evolving a dull colouration, the potential costs involved in the bright pigments production are
avoided. Several factors will have to be clarified to test the feasibility of this proposed
75
scenario. Other than the already mentioned possible fluctuations in toxicity and the
questionable ecological significance of the toxicity essay used, information on the pigments
involved in dendrobatids pigmentation are necessary to evaluate the actual cost of pigment
production.
4.2.5 Role of sexual selection
As discussed before, together with the role of natural selection mediated by predators, sexual
selection has been suggested to play an important role in the diversification of aposematic
signals in poison-dart frogs. Females show preference for brighter (Maan & Cummings, 2009)
and more colourful males (Maan & Cummings, 2008) as well for males of their own
population in O. pumilio (Summers et al., 1999; Reynolds & Fitzpatrick, 2007; Maan &
Cummings, 2008). I showed here, that aposematic red and cryptic green morphs have a
different pulse rate in the male advertisement call in the northern populations. A significant
differentiation in this key sexual signal indicates that the females may potentially select males
of their own colour, similarly with what has been observed in the congeneric species O.
pumilio.
76
5. Conclusion
The present work provides evidence for deep intraspecific divergence in the polymorphic
aposematic poison-dart frog Oophaga granulifera. I described the patterns of geographical
variation in historical and recent genetic structure and in key phenotypic traits such as
morphology and advertisement call. The data here presented all congruently show that the
southern and northern lineages identified are clearly diverging and may well represent
different species. The phylogeographic reconstruction and the recent population structure
indicate that the river Río Térraba is likely to be the geographic barrier between the lineages
that
are,
therefore,
geographically,
genetically
and
phenotypically
separated.
As concerned to the recent evolution of colour diversity in O. granulifera, several factors may
potentially be involved in the origin and maintenance of this notable differentiation.
Alongside correlation data such as those here presented future research efforts will be
necessary to empirically evaluate the effective strength in mating preferences shaping the
observed variation in colouration. Moreover, many aspects of dendrobatid ecology, such as
actual predator community, prey community and related spatial and temporal variation in the
acquired toxicity, will have to be clarified to define a clearer evolutionary scenario explaining
the reason of the remarkable colour variation in this aposematic vertebrate.
77
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Additional Information
1. Sequences accession numbers
List of all sequences used in the study. Samples specifically sequenced for the present work
are marked with *. Table reports, sampled animal, sampling site (and code) and the haplotype
code (with relative accession number). For samples sharing the same haplotype identified in
the present study, the accession number is reported only once.
ID
Sampling site [code]
Cyt b (AccN°)
16S (AccN°)
O. granulifera 1-CH*
Charcos [CH]
HE775251 (H1)
HE804764 (1)
O. granulifera 2-CH*
Charcos [CH]
HE775251 (H1)
HE804764 (1)
O. granulifera 3-CH*
Charcos [CH]
HE775252 (H2)
HE804765 (2)
O. granulifera 4-VE*
Ventana [VE]
HE775253 (H3)
O. granulifera 5-VE*
Ventana [VE]
HE775253 (H3)
O. granulifera 6-PA*
Palmar [PA]
HE775254 (H4)
HE804766 (3)
O. granulifera 7-PA*
Palmar [PA]
HE775255 (H5)
HE804766 (3)
O. granulifera 8-PA*
Palmar [PA]
HE775256 (H6)
HE804766 (3)
O. granulifera 9-FS*
Firestone [FS]
HE775257 (H7)
HE804767 (4)
O. granulifera 10-FS*
Firestone [FS]
HE775257 (H7)
O. granulifera 11-FS*
Firestone [FS]
HE775258 (H8)
HE804767 (4)
O. granulifera 12-BA*
Baru [BA]
HE775258 (H8)
HE804767 (4)
O. granulifera 13-BA*
Baru [BA]
HE775259 (H9)
O. granulifera 14-BA*
Baru [BA]
HE775260 (H10)
O. granulifera 15-DO*
Dominical [DO]
HE775257 (H7)
HE804767 (4)
O. granulifera 16-DO*
Dominical [DO]
HE775257 (H7)
HE804767 (4)
O. granulifera 17-DO*
Dominical [DO]
HE775257 (H7)
111
O. granulifera 18-MA*
Matapalo [MA]
HE775257 (H7)
O. granulifera 19-MA*
Matapalo [MA]
HE775257 (H7)
O. granulifera 20-MA*
Matapalo [MA]
HE775258 (H8)
O. granulifera 21-MA*
Matapalo [MA]
HE775262 (H12)
O. granulifera 22-PL*
Portalon [PL]
HE775257 (H7)
O. granulifera 23-PL*
Portalon [PL]
HE775257 (H7)
O. granulifera 24-PL*
Portalon [PL]
HE775261 (H11)
HE804767 (4)
O. granulifera 25-SA*
Savegre [SV]
HE775257 (H7)
HE804767 (4)
O. granulifera 26-DA*
Damitas [DA]
HE775257 (H7)
HE804768 (5)
O. granulifera 27-DA*
Damitas [DA]
HE775257 (H7)
O. granulifera 28-DA*
Damitas [DA]
HE775257 (H7)
O. granulifera Wang0925-FC
Fila Chonta [FC]
HQ841077 (H7)
O. granulifera Wang0927-FC
Fila Chonta [FC]
HQ841078 (H16)
O. granulifera Wang0928-FC
Fila Chonta [FC]
HQ841079 (H15)
O. granulifera Wang0929-CN
Cerro Nara [CN]
HQ841080 (H15)
O. granulifera Wang0930-CN
Cerro Nara [CN]
HQ841081 (H7)
O. granulifera Wang0931-CN
Cerro Nara [CN]
HQ841082 (H15)
O. granulifera Wang0932-DM
Rio Damitas [DM]
HQ841083 (H15)
O. granulifera Wang0933-DM
Rio Damitas [DM]
HQ841084 (H7)
O. granulifera Wang0934-DM
Rio Damitas [DM]
HQ841085 (H15)
O. granulifera Wang0939-SV
Rio Savegre [SV]
HQ841086 (H7)
O. granulifera Wang0940-SV
Rio Savegre [SV]
HQ841087 (H7)
O. granulifera Wang0941-SV
Rio Savegre [SV]
HQ841088 (H7)
O. granulifera Wang1007-BR
Rio Baru [BR]
HQ841089 (H10)
O. granulifera Wang1009-BR
Rio Baru [BR]
HQ841090 (H8)
O. granulifera Wang1010-BR
Rio Baru [BR]
HQ841091 (H10)
O. granulifera Wang1012-PB
Piedras Blancas [PB]
HQ841092 (H14)
O. granulifera Wang1014-PB
Piedras Blancas [PB]
HQ841093 (H13)
HE804767 (4)
HE804767 (4)
112
O. granulifera Wang1015-PB
Piedras Blancas [PB]
HQ841094 (H14)
O. granulifera Wang1016-TE
Río Térraba [TE]
HQ841095 (H14)
O. granulifera Wang1017-TE
Río Térraba [TE]
HQ841096 (H14)
O. granulifera Wang1018-TE
Río Térraba [TE]
HQ841097 (H14)
O. granulifera Wang1019-DB
Drake Bay [DB]
HQ841098 (H14)
O. granulifera Wang1020-DB
Drake Bay [DB]
HQ841099 (H14)
O. granulifera Wang1021-DB
Drake Bay [DB]
HQ841100 (H14)
O. granulifera Wang1022-CO
Corcovado [CO]
HQ841101 (H14)
O. granulifera Wang1024-CO
Corcovado [CO]
HQ841102 (H14)
O. granulifera Wang1026-CO
Corcovado [CO]
HQ841103 (H14)
Oophaga histrionica
_
HQ841104
DQ502032
Oophaga sylvatica
_
HQ290567
AY364569
Oophaga arborea
_
DQ502036
Oophaga lehmanni
_
DQ502034
Oophaga pumilio-N
Nicaragua
DQ502235
Oophaga pumilio-S
Panama
EU342663
Oophaga speciosa
_
DQ502037
Oophaga vicentei
_
DQ502167
Dendrobates leucomelas
_
AF124119
Dendrobates tinctorius
DQ768797
113
2. Population structure ∆K results
114
Ackowledgments
Thanks to the Volkswagen foundation for the very generous resources provided.
Thanks to the MINAE for releasing research permits.
Thanks to Heike (Pröhl) for giving an opportunity to an unknown student from Italy.
Thanks to Nick (Mundy) for letting me enter in his lab at the University of Cambridge.
Thanks to Eberhard Meyer for providing information on some frog populations’ locations.
Thanks to Adriana Bellati for advising on molecular data analysis.
Thanks to Sabine Sippel for her collaboration in the lab.
Thanks to Sönke von den Berg for helping with graphics.
Thanks to Cristina who has been an important support during several years.
Thanks to my parents who are still doing an effort to understand where I want to go.
Thanks to all people who helped me out during the crazy time in the field.
Thanks to the tiny granular poison frogs for existing.
Thanks to the lethal snakes of Costa Rica for leaving me alive and able to conclude this work.
Thanks to Costa Rica cause I realized there is not just one way to live.
Thanks to Germany and England cause I understood cultural differences may be funny.
Thanks to Julia for showing me one does not need many things to be happy.