JOURNAL OF CRUSTACEAN BIOLOGY, 30(4): 589-596, 2010
REPRODUCTIVE BIOLOGY IN FEMALES OF AEGLA STRINATII (DECAPODA: ANOMURA: AEGLIDAE)
Sérgio Schwarz da Rocha, Roberto Munehisa Shimizu, and Sérgio Luiz de Siqueira Bueno
(SSR, correspondence, [email protected]) Centro de Ciências Agrárias, Ambientais e Biológicas, Universidade Federal do Recôncavo
da Bahia (UFRB), CEP: 44380-000, Cruz das Almas, Bahia, Brazil;
(RMS, [email protected]) Departamento de Ecologia, Instituto de Biociências, Universidade de São Paulo, Rua do Matão, travessa 14,
nu 321, Cidade Universitária, CEP: 05508-900, São Paulo, Brazil;
(SLSB, [email protected]) Departamento de Zoologia, Instituto de Biociências, Universidade de São Paulo, Rua do Matão, travessa 14,
nu 101, Cidade Universitária, CEP: 05508-900, São Paulo, Brasil
ABSTRACT
Females of Aegla strinatii (n 5 466) were sampled monthly (September 2003 to September 2005) by means of sieves and traps from Rio
das Ostras (24u38916.20S; 48u24905.20W), at Jacupiranga State Park, South of São Paulo State, Brazil. The reproductive period was
markedly seasonal (from May to September) encompassing the Austral late autumn through late winter. This is in accordance to the
pattern of reproductive period variations in relation to the latitudinal climate variability verified in species of Aegla. The proportion of
adult females exhibiting the ovigerous condition was higher in young/small specimens as compared to old/large ones, and suggests the
occurrence of senescence in the latter group. Average size at the onset of functional maturity in females was estimated as 16.66 mm of
carapace length (rostrum excluded). The number of eggs per ovigerous females ranged from 1 to 325. Eggs are slightly elliptical and
average size varied according to embryonic stage. Mean (6 standard deviation) carapace length of juveniles (n 5 118) was 1.50 6
0.05mm (range: 1.40-1.65mm).
KEY WORDS: Aegla strinatii, reproduction
DOI: 10.1651/10-3285.1
troglomorphic adaptations are reported (Bond-Buckup and
Buckup, 1994; Alves Jr., 2007). Specimens of Aegla strinatii
Türkay, 1972 are troglophiles, that is, self-sustained
populations are found inside and outside the cave, with free
transit between both environments (Rocha and Bueno,
2004). The areas of occurrence of A. strinatii have been
reported for its type-locality and few adjacent areas of the
Rio das Ostras system (Türkay, 1972; Bond-Buckup and
Buckup, 1994; Rocha and Bueno, 2004). No information
regarding the biology of A. strinatii is currently available.
This study presents results on the population structure
and reproductive pattern of the population of A. strinatii
from the type-locality at Jacupiranga State Park, south of
São Paulo State, Brazil. We expect that the information
presented herein will be useful in future studies regarding
the evaluation of the risk of extinction of this species
according to the criteria established by the IUCN (2001).
INTRODUCTION
Aeglidae Dana, 1852 comprise two extinct genera, Haumuriaegla and Protoaegla, from marine sediment (Feldmann,
1984; Feldmann et al., 1998), and one extant genus Aegla
Leach, 1820; the latter has over 60 freshwater species
endemic to temperate and subtropical regions of continental
South America (Schmitt, 1942; Bond-Buckup and Buckup,
1994; Bond-Buckup, 2003). The meridional and septentrional limits of geographical distribution of living aeglids are
the island of Madre de Dios (50u019100S; 075u189450W) in
Chile, and Clavaral (20u189470S; 047u169370W) in Brazil,
respectively (Jara and López, 1981; Bueno et al., 2007).
Taxonomic reviews of Aeglidae based mainly on morphology (Bond-Buckup and Buckup, 1994) and molecular data
(Pérez-Losada et al., 2004) are available.
These anomuran decapods inhabit freshwater streams
and lakes, and are usually found hidden under stones and
pebbles, or leaf litter accumulated in the river bed during
daytime, and show increased ambulatory activity at night
(Bond-Buckup, 2003; Bueno et al., 2007). They are
omnivorous, feeding on animal debris, algae, and invertebrate larvae (Bahamond and Lopez, 1961; Rodrigues and
Hebling, 1978; Magni and Py-Daniel, 1989).
The biology of aeglids is still poorly known, especially for
those species which show high endemism, and inhabit carstic
regions, as in the Ribeira do Iguape River Basin, south of São
Paulo State (Trajano and Gnaspini-Neto, 1990; Rocha and
Bueno, 2004). In this region, three troglobite species (Aegla
microphthalma Bond Buckup and Buckup, 1994, A.
leptochela Bond-Buckup and Buckup, 1994, and A.
cavernicola Türkay, 1972) exhibiting varied degrees of
MATERIALS AND METHODS
Specimens of A. strinatii were collected monthly, from September 2003 to
September 2005, from a 300-meter long section of the Ostras stream
(24u38916.20S; 048u24905.20W), at Jacupiranga State Park, the second
largest conservation unit in the state of São Paulo, which extends over an
area equivalent to 150,000 hectares (Fig. 1) (Clauset, 1999). Local
temperature ranges from 19.8uC to 27.7uC (mean 6 SD 5 23.0 6 2.9uC)
and seasonal rainfall regime (mean 6 SD 5 126.2 6 62.9 mm) with dry
weather (49-89 mm) prevailing from May to September (late Austral
autumn to early spring) (EMBRAPA/ESALQ-USP, 2003).
Aeglid specimens were either sampled manually with a sieve (diameter
50 cm, mesh 0.5 mm) to capture specimens hidden under rocks, or under
leaf litter accumulated at the bottom of the river; or captured with baited
traps distributed randomly throughout the working area. These traps were
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Fig. 1. Map of the southern region of the state of São Paulo, Brazil,
indicating the extension limits of the Ribeira do Iguape River Basin. The
grey area depicts the Jacupiranga State Park. Inset: State of São Paulo.
set overnight and were inspected for captured animals in the following
morning. Commercially available dried cat feed containing fish meal as
one of the main ingredients was used as bait as described by Bueno et al.
(2007).
Sex determination was based on the observation of the genital pores on
the coxa of the third pair of pereiopods in females, and by the presence or
lack of pleopods in females and males, respectively (Martin and Abele,
1988). Carapace length (CL) was measured from the orbital sinus to the
mid-posterior border, behind the areolar area to the nearest 0.01 mm with
the aid of a digital caliper. The distance from the tip of the rostrum to the
mid-posterior border of the carapace (carapace length with rostrum
included, or CLR) was also measured. The CLR vs. CL relationship was
described by the function CLR 5 1.011CL + 0.1283 (r2 5 0.98) for adult
females thus allowing comparisons of the results of the present study with
those published by other authors in which the carapace length was
measured with the rostrum included (Bahamonde and López, 1961; Jara,
1977; Hebling and Rodrigues, 1977; Swiech-Ayoub and Masunari, 2001;
Fransozo et al., 2003; Viau et al., 2006). The average carapace length at
onset of morphometric maturity in females (16.18 mm; Rocha et al.,
unpublished data) was used for the recognition and separation of
specimens into juvenile or adult groups in this sex.
In live female specimens, ovaries at late maturation stage were clearly
visible to the naked eye through the translucent thin exoskeleton of the
ventral side of the pleon as two parallel strands running posteriorly.
Macroscopic evaluation of the ovaries at this developmental stage
followed criteria described by Bueno and Shimizu (2008) for Aegla
franca Schmitt, 1942, who devised four sequential stages based mainly on
the extension of the gonads relative to the pleopods as a convenient mean
to help the recognition of impending oviposition under field conditions.
The reproductive period was based on the monthly observation of
ovigerous females in the population. Average size at the onset of
functional maturity was determined as the CL at which 50% of the females
sampled during the reproductive period were considered sexually mature
adults by exhibiting one of the following reproductive traits: ovaries at late
development stage 2 (at least one of the posterior lobes reaching or slightly
overreaching the second pair of pleopods) or beyond, ovigerous or postovigerous condition (Bueno and Shimizu, 2008). The latter condition was
recognized either by the presence of newly-hatched juveniles protected in
the brooding chamber formed by the flexed pleon of the female or by the
observation of ovigerous setae on the pleopods soon after parental care was
completed (Bueno and Shimizu, 2008). Average size at the onset of
functional maturity was determined by interpolation of the equation
obtained by performing logistic regression (Pagano and Gauvreau, 2006)
on maturation condition of specimen (immature 5 0; mature 5 1) vs CL
data points.
Eggs were examined and counted under field conditions with the aid of
a Bausch & Lomb dissecting scope, and without removing them from the
female pleopods (Bueno and Shimizu, 2008). Eggs that had accidentally
fallen off the pleopods during egg manipulation were included in the
counting procedure, staged according to embryonic stages of development
– early, intermediate or late eggs – as described in Bueno and Shimizu
(2008), fixed in 70% ethanol, and measured. The lengths of the major and
the minor axes of the eggs were measured under a dissecting microscope
(Zeiss Stemi SV6) equipped with a micrometric scale following
procedures described in Bueno and Rodrigues (1995) and Bueno and
Shimizu (2008). Possible variation in egg dimensions between early and
late stages of embryonic development was verified with the nonparametric Mann-Whitney test (Zar, 1996).
Three ovigerous females of A. strinatii carrying eggs at late embryonic
developmental stage were collected in August 2004 and were transported
to the Laboratory of Carcinology of the Instituto de Biociências,
Universidade de São Paulo, state of São Paulo in a container half filled
with continuously aerated water from the study site. The specimens were
kept in an aquarium and had the flexed pleon checked periodically for the
presence of recently hatched juveniles. These juveniles were carefully
removed and immediately preserved in 70% alcohol. Carapace length (CL)
was measured from the posterior border of the orbital sinus to midposterior border of the cephalothorax (Francisco et al., 2007) under a
dissecting scope equipped with an ocular micrometer disc.
Except for the ovigerous females and newly-hatched juveniles
mentioned above, all other specimens sampled were returned alive to the
stream after measurements and observations were completed during this
investigation. Voucher male and female specimens from this very study
site were collected previously (Rocha and Bueno, 2004) and were
deposited at the Museu de Zoologia (MZUSP #15026), University of São
Paulo.
RESULTS
Of the total of 867 specimens of A. strinatii sampled, 466 were
females. Late ovarian development stage 2 or beyond were
recorded from February to April 2004 (with one exception in
June and another one in July, both at developmental stage 2),
and from January to May 2005 (Fig. 2A).
Ovigerous females were sampled from May to September in 2004 and 2005, except in June 2005, when no adult
females were sampled. Females bearing late eggs were last
observed by September, including the year of 2003 when
this study began. In 2004, the sampling of post-ovigerous
females was restricted to October, while this condition was
observed in August and September (no sampling done in
October) in the following year (Fig. 2B). Field notes on the
post-ovigerous condition were not taken in 2003.
Carapace length of ovigerous females ranged from 15.63
to 24.45 mm, and the average size at the onset of functional
maturity in this sex was estimated as 16.66 mm of CL
(16.97 mm of CLR) (Fig. 3). When data regarding
ovigerous/post-ovigerous females during the reproductive
period are distributed according to size classes (Fig. 4), the
percentage of sexually mature females increased gradually
from 15-16 mm CL class to 20-21 mm class in which all
females exhibited this condition. In size classes higher than
21 mm of CL, a decrease in the percentage of reproductive
females is observed.
The number of eggs counted from 25 ovigerous females
varied from 1 to 325 (Table I). Mean length of major and
minor axes of the eggs were respectively 1.31 (6 0.07) mm
and 1.21 (6 0.07) mm at early stage (n 5 34 from 3
females), 1.45 (6 0.08) mm and 1.34 (6 0.07) mm at
intermediate stage (n 5 60 from 8 females) and 1.51
(6 0.06) and 1.39 (6 0.06) at late stage (n 5 43 from 13
females). Significant size difference between early and late
eggs were observed when corresponding major (U 5 14; P
% 0.001) and minor (U 5 37.5; P % 0.001) axes were
compared. Mean (6 standard deviation) carapace length
of juveniles (n 5 118) was 1.50 6 0.05 mm (range: 1.401.65 mm).
ROCHA ET AL.: REPRODUCTION OF AEGLA STRINATII
591
Fig. 2. Aegla strinatii: Temporal variation in the proportions of the ovarian developmental stages (A) and of ovigerous (embryonic development of eggs
discriminated) and postovigerous females (B). The values showed above each bar represents the total number of females sampled in each month. All
criteria based on Bueno and Shimizu (2008).
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JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 30, NO. 4, 2010
Table 1. Ovigerous females of Aegla strinatii sampled from September
2003 to September 2005. * Low number possibly due to egg loss.
Excluded data from the fecundity analysis only.
Fig. 3. Aegla strinatii. Size at the onset of functional maturity of females
estimated by logistic regression based on the absence (0) or presence (1) of
discrete reproductive traits plotted against carapace length.
DISCUSSION
Several environmental cues have been suggested as factors
that could influence the reproductive period of aeglids,
such as temperature, photoperiod, food availability and
water cleanness (Bahamonde and Lopez, 1961; Bueno and
Bond-Buckup, 2000; Swiech-Ayoub and Masunari, 2001;
Noro and Buckup, 2002). More recently, Bueno and
Shimizu, (2008) suggested that latitudinal gradients of
variability in temperature and in rainfall regime (with direct
influence on stream flow velocity) may strongly affect
reproductive period of aeglid species, which tends to be
shorter in localities under larger rainfall variation (SD .
60 mm) and smaller temperature variability (SD , 2.5uC)
than in sites with opposite climate conditions.
A seasonal reproductive cycle concentrated mainly from
autuan to winter seasons, as observed in A. strinatii, is a
fairly common pattern among many aeglid species (see
Table 3 in Bueno and Shimizu, 2008 for review), with few
known exceptions (Bueno and Bond-Buckup, 2000;
Fransozo et al., 2003; Colpo et al., 2005; Viau et al.,
2006). The five-month reproductive period of A. strinatii
fits well into the pattern of reproductive period variations in
Fig. 4. Aegla strinatii. Proportion of ovigerous and post-ovigerous females
during the reproductive period, distributed according to carapace length class.
Date
Carapace
length (mm)
Embryonic
development stage
September 2003
September 2003
June 2004
June 2004
June 2004
July 2004
July 2004
July 2004
July 2004
July 2004
August 2004
August 2004
August 2004
August 2004
August 2004
September 2004
September 2004
September 2004
September 2004
May 2005
July 2005
July 2005
August 2005
September 2005
September 2005
Mean 6 SD
16.23
20.06
21.03
22.18
23.34
23.35
23.3
22.09
24.45
23.54
18.41
16.09
16.29
22.13
21.20
19.85
18.68
15.63
20.98
21.46
20.52
23.41
20.11
18.59
20.15
20.18 6 2.49
Late
Late
Early
Early
Early
Intermediate
Intermediate
Intermediate
Intermediate
Intermediate
Late
Late
Intermediate
Late
Late
Late
Late
Late
Late
Early
Intermediate
Intermediate
Late
Late
Late
Number of eggs
288
2*
14*
19*
2*
17*
73
117
325
129
249
177
298
87
112
5*
1*
4*
5*
180
80
5*
219
9*
6*
relation to climate conditions as proposed by Bueno and
Shimizu (2008) for Aegla species (Fig. 5).
Although females of A. strinatii attain maturity at a larger
size (16.45 mm of CL) than those of A. franca (12.75 mm
CL) both species become sexually functional and mate by
early autumn approximately 21 months (Bueno and Shimizu,
2008; Rocha et al., in preparation) after hatching. For A.
strinatii, this age corresponds to 20,66 mm CL (21.02 mm
CLR), as estimated by interpolation of the growth curve
function (Rocha et al., unpublished data). Thus, the highest
proportion of reproductive female observed in 20-21 mm CL
class (100%) suggests that the reproductive performance
peak (Fig. 4) is strongly related to the first mating period of
females by the time functional maturity is attained.
The decrease in proportion of females that did not become
ovigerous during the reproductive period in size-classes
higher than 20-21 mm of CL (Fig. 4) suggests a decline in the
breeding activity of the largest females in the population.
Differently from A. franca, which reproduces only once
during an estimated lifespan of 28.4 months (Bueno and
Shimizu, 2008), the lifetime expectancy of females of A.
strinatii was estimated as 34 months (Rocha et al.,
unpublished data) which enables the adults to live long
enough to reproduce a second time by the next breeding
season. However, these older females appear to contribute
less intensely than the sexually matured cohort of one-year
younger adult individuals. This condition suggests the
occurrence of senescence, in which survival and reproductive
performance decline with increased age after full sexual
maturity is attained (Charlesworth, 1993). An evolutionary
explanation of senescence in gonochoristic animal populations has been proposed (see Charlesworth, 1993; Reznick,
ROCHA ET AL.: REPRODUCTION OF AEGLA STRINATII
Fig. 5. Variation in length of the reproductive period of aeglid species in
relation to latitude (A), the temperature variability (B), and rainfall
variability (C). The black triangle represents Aegla strinatii from Ostras
stream. All species references from Bueno and Shimizu (2008) except that
of A. schmitti, obtained from Teodósio and Masunari (2009).
1993, for review), and, regardless of the specific evolutionary
mechanisms behind each theory, the end result indicates
that natural selection strongly favors survival and higher
reproductive output early in life (Charlesworth, 1993).
Therefore, older senescent individuals tend to show less
importance in the adult population in terms of number of
individuals due to higher mortality rate, as well as in terms of
actual reproductive output.
While in females of A. strinatii such reproductive
senescence period may extend for approximately one year
starting at the completion of the first reproductive period,
females of A. franca reproduce only once in their lifetime
before apparently becoming senescent and rapidly disappear from samples by the end of the reproductive period
(Bueno and Shimizu, 2008; Bueno and Shimizu, unpub-
593
Fig. 6. Variation in carapace length of aeglid species juveniles in relation
to the latitude (A), the temperature variability (B), and rainfall variability
(C). References are the same of those of Table 2. The carapace lengths of
Aegla schimitt (*) which were originally measured with rostrum included
(CLR, Masunari, personal communication) were converted to approximate
measures taken excluding rostrum (CL), using CL/CLR ratio obtained
from Figure 1 by Teodósio & Masunari (2007).
lished data). The extension of the senescence period with
species might vary considerably according to their life
history patterns. In anostracan crustaceans, Browne (1980)
observed that senescence period in five strains of Artemia
was significantly shorter than the previous and much longer
reproductive period.
Senescence in females of some species of pleocyemate
decapod has been addressed as the decline in the number of
eggs per brood or increasing brood egg loss, expressed by a
negative allometry relationship from early to late embryonic stages, when larger (older) specimens to smaller
(younger) are compared (Shields, 1991; Torres et al.,
2007). In some decapod species, such negative allometry
has not been observed, and were considered to exhibit no
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JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 30, NO. 4, 2010
Table 2 Carapace length of aeglid species juveniles (CL: rostrum not included; CLR: rostrum included) in different geographical localities and climatic
regimes. Data are ordered in relation to latitude.
Annual mean 6 SD
Species
1
A.
A.
A.
A.
franca
strinatii2
schmitii3
ligulata4
A.
A.
A.
A.
platensis5
longirostri6
violacea7
prado8
Aegla abtao9
Study site
Latitude (S)
Climate data
source
Claraval
Jacutinga
Mananciais da Serra
São Francisco de
Paula**
Taquara**
Itaara**
Mariana Pimentel
Estação Ecológica
do Taim
Valdivia - Chile
20u189470
24u38916.20
25u299460
29u269520
Franca
Jacutinga
Curitiba
Caxias do Sul
20.2
23.0
16.5
16.3
6
6
6
6
2.0
2.9
2.7
3.2
29u469
29u249
30u219100
32u329
Porto Alegre
Santa Maria
Porto Alegre
Pelotas
19.5
18.8
19.5
17.8
6
6
6
6
3.9
4.1
3.9
4.1
39u299
Valdivia Chile
11.4 6 3.3
Temperature (uC)
Rainfall (mm)
Range
Carapace length
(mean 6 SD)
128.8
126.2
117.3
159.6
6
6
6
6
104.6
62.9
27.8
28.1
1.58-1.79
1.40-1.65
1.96-2.01
1.42-1.58
1.71
1.50 6 0.06
1.99
1.50
CL
CL
CLR*
CL
112.3
140.5
112.3
113.9
6
6
6
6
16.1
8.9
16.1
18.8
1.01-1.39
1.39-1.48
1.01-1.38
1.02-1.36
1.20
1.44
1.20
1.19
CL
CL
CLR
CL
n.a.
1.41 6 0.10
203.4 6 128.0
Method
n.a
* S. Masunari, personal communication.
** Precise location of sampling site not informed in Bond-Buckup et al. (1999); name of the nearest sampling site taken from other authors, as shown in brackets under references 4,5 and 6 below.
n.a. 5 not available.
1
Francisco et al. (2007).
2
Present study.
3
Teodósio and Masunari (2007) [measurement method from Teodósio & Masunari, 2009].
4
Bond-Buckup et al. (1999) [study site data from Oliveira et al. (2003)].
5
Bond-Buckup et al. (1999) [study site data from Lizardo-Daudt & Bond-Buckup (2003)].
6
Bond-Buckup et al. (1999) [study site data from Colpo et al. (2005].
7
Bueno & Bond-Buckup (1996).
8
Bond-Buckup et al. (1996).
9
Jara & Palacios (2001). Climate data from EMBRAPA/ESALQ-USP (2003) for the Brazilian localities and from World Climate (2007) for the Chilean locality.
senescence period (Calado and Narciso, 2003; Penha-Lopes
et al., 2007; Figueiredo et al., 2008). In the present paper,
such analytical approach regarding fecundity was not
possible due to the number of ovigerous females sampled,
which prevented the definition of representative size/age
groups, in addition to insufficient or even lack of data of
specific embryonic stages within each group (Table 1).
Nearly half of the ovigerous females of A. strinatii
(48.0%) carried less than 20 eggs attached to the pleopods,
regardless of the embryonic stage (Table 1). Unfertilized
eggs, egg manipulation (cleaning), and the escaping
reaction by violently flexing the pleon are some factors
that might cause loss of eggs during embryonic development. Unsuccessful oviposition, expressed as failure to
attach most eggs to the pleopods, has also been suggested
as a possible explanation of females carrying very few early
eggs as observed in A. franca (Bueno and Shimizu, 2008).
In the present study, three out of four ovigerous females of
A. strinatii carried few early eggs and were larger than
21 mm of CL, which suggests that the senescence factor
may also be considered in this case, but this hypothesis
should be further tested properly.
Similarly to A. franca (Bueno and Shimizu, 2008), the
temporal patterns of ovarian and embryonic development
strongly indicate that A. strinatii produces a single egg mass
during the seasonal reproductive period (late autumn to early
spring). The average duration of egg incubation of a single
ovigerous female extends for approximately 3 to 4 months
within the five month-long reproductive period (Fig. 2B).
This differs markedly from the pattern observed in females of
Aegla platensis Schmitt, 1942 and Aegla uruguayana Schmitt,
1942 kept in laboratory conditions which incubated eggs
for # 35 days and 45 to 50 days, respectively (Lizardo-Daudt
and Bond-Buckup, 2003; López-Greco et al., 2004). These
two latter species occur in higher latitudes than A. strinatii
and A. franca, and reproduce continuously throughout the
year (Bueno and Bond-Buckup, 2000; Viau et al., 2006).
Published information about the increase in egg size
during embryonic development in aeglids is scant. Aegla
strinatii and A. franca are the only species for which a
significant difference in egg length during embryonic
development stages has been reported (Bueno and Shimizu,
2008; this paper). On the other hand, eggs of Aegla prado
Schmitt, 1942 from Uruguay and A. platensis from
southern Brazil did not exhibit an increase in size during
embryonic development (Verdi, 1985; Lizardo-Daudt and
Bond-Buckup, 2003).
Francisco et al. (2007) reported that the newly-hatched
juveniles of A. franca were larger (CL in mm, rostrum
excluded) than those of some aeglids from temperate
habitats, for which descriptions were available by then (see
Rodrigues and Hebling, 1978; Bond-Buckup et al., 1996,
1999; Bueno and Bond-Buckup, 1996). With the addition
of data on juveniles of A. strinatii along with those of A.
abtao Schmitt, 1942 and A. schmitti Hobbs, 1979 (Jara and
Palacios, 2001; Teodósio and Masunari, 2007) to this
dataset, a trend of decreasing juvenile size with latitude
becomes apparent (Table 2; Fig. 6A). Variation of juvenile
size is related to variability (rather than mean value) of the
major climatic variables, increasing towards locations with
wide temperature range and narrowly varying rainfall
(Fig. 6B–C), a trend observed previously for the length of
reproductive period in aeglids (Bueno and Shimizu, 2008).
Most data available regarding reproductive traits in Aegla
come from temperate species sampled from river courses
from the Uruguay Basin and from subtropical species
sampled from the Paraná and the Ribeira do Iguape Basins.
The information on variation of incubation time, size
variation of the egg during brooding, and juvenile size
compiled in this study, in conjunction with those on variation
of reproductive period duration and of the egg size-fecundity
relationship among aeglids (Bueno and Shimizu, 2008),
strongly points to a differentiation of reproductive pattern
between temperate and subtropical species (Table 3).
ROCHA ET AL.: REPRODUCTION OF AEGLA STRINATII
Table 3. Differences on reproductive pattern between temperate and
subtropical species of Aegla.
Temperate species
Reproductive
period
Egg size
and fecundity
Incubation time
Egg growth
during incubation
Juvenile size
Sub-tropical species
Longer
Shorter
Higher number
of smaller eggs
1-2 months
No
Lower number of
larger eggs
3-4 months
Yes
Smaller
Larger
The reproductive pattern as described for temperate
species herein may express the original condition shared by
early freshwater eaglids. In a recent study on the phylogeny
and biogeography of freshwater aeglids, Pérez-Losada et al.
(2004) discussed the Pacific-origin of the group during the
Late Cretaceous marine transgression and provided strong
support to the hypothesis of the eastern radiation of the group
along freshwater paleodrainage systems of southern South
America in the Tertiary period. Of the five phylogenetic
clades recognized by Pérez-Losada et al. (2004), three
comprises aeglid species presently found mostly in the
eastern side of the continent. The sister group formed by
clades D and E (as indicated in Pérez-Losada’s work)
contains temperate species from the Uruguay Basin (Uruguay
and Southern Brazil) for which reproductive data are depicted
in Table 3. Clade C (see Pérez-Losada, 2004) includes
species from tributaries of the Paraná drainage system and the
presently isolated Ribeira do Iguape Basin. Although clade C
contains several temperate species it also contains all
subtropical species that radiated towards lower latitudes
and managed to survive and adapt to new environmental
conditions characterized by larger rainfall variation (SD .
60 mm) and smaller temperature variability (SD , 2.5uC) as
compared to temperate regions of South America. Considering the hypothesis that habitat conditions at lower latitudes
depart from optimal reproduction conditions required by
temperate aeglid species (Bueno and Shimizu, 2007), it is our
understanding that the distinct reproductive pattern exhibited
by subtropical species of aeglids (Table 3) could be viewed
as a clear adaptative response to the colonization of
freshwater habitats in lower latitudes.
ACKNOWLEDGEMENTS
The authors would like to express their sincere thankfulness to Dr.
Emerson C. Mossolin for his help in sampling the specimens. The authors
also thank CNPq (grant # 14112/2004-9) and CAPES for providing the
financial support that made possible the present study. Finally, we would
like to acknowledge our gratitude to all the staff members at Jacupiranga
State Park and Instituto Florestal, São Paulo State.
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RECEIVED: 12 January 2010.
ACCEPTED: 22 March 2010.