Blackwell Science, LtdOxford, UKBOJBotanical Journal of the Linnean Society0024-4074The Linnean Society of London, 2003
141
Original Article
PHYLOGEOGRAPHY OF ANDROSACE BREVIS
and A. WULFENIANA
P. SCHÖNSWETTER ET AL.
Botanical Journal of the Linnean Society, 2003, 141, 437–446. With 5 figures
Disjunctions in relict alpine plants: phylogeography of
Androsace brevis and A. wulfeniana (Primulaceae)
PETER SCHÖNSWETTER*, ANDREAS TRIBSCH, GERALD M. SCHNEEWEISS and
HARALD NIKLFELD
Institute of Botany, University of Vienna, Rennweg 14, A-1030 Vienna, Austria
Received January 2002; accepted for publication October 2002
Amplified Fragment Length Polymorphism (AFLP) was used to clarify the glacial history of the rare, disjunctly distributed, alpine cushion plant Androsace wulfeniana, which is endemic to the Eastern Alps (Austria and Italy). Disjunct populations in the Dolomites are genetically very distinct from those in the main distributional area. It is
hypothesized that they are descendants of long-term isolated glacial survivors and are not a result of recent longdistance dispersal. Within the main distributional area of the species in the central Eastern Alps, two groups of
populations can be distinguished, which are congruent with hotspots of rare relictual vascular plant taxa. In the
taxonomically closely related A. brevis growing in the Southern Alps (Italy, Switzerland), no genetic-geographical
structure was found. Genetic variation is extremely low in disjunct populations of A. wulfeniana in the Dolomites
and in A. brevis. In contrast, in the main distributional area of A. wulfeniana, genetic variation is similar to that of
the colonizing widespread congener A. alpina. © 2003 The Linnean Society of London, Botanical Journal of the
Linnean Society, 2003, 141, 437–446.
ADDITIONAL KEYWORDS: AFLP – endemism – genetic variation – glacial survival – widespread
congener.
INTRODUCTION
Disjunctions are a striking biogeographical aspect
exhibited by taxa of different ranks and on different
geographical scales. Well documented examples on the
smaller scale are provided by mountain ranges like
the European Alps (Merxmüller, 1952, 1953, 1954).
Disjunctions often result in allopatric speciation. An
excellent example in the Alps is provided by members
of Primula sect. Auricula, where in several subsections para- and allopatric species occur in parallel
(maps in Merxmüller, 1952; Meusel et al. 1978). Disjunctions, however, need not be accompanied by a
speciation event, leading instead to intraspecific disjunctions.
Intraspecific disjunctions can be caused by ecological or historical factors. A well-known example of the
former is substrate specificity, e.g. calciphilous species
distributed in the northern and the southern Calcar*Corresponding author. E-mail: peter.schoenswetter@
univie.ac.at
eous Alps (examples in Merxmüller, 1952, 1953, 1954).
As a historical factor, Pleistocene glaciations have
been regarded as a driving force in generating disjunctions in the Alps (e.g. Merxmüller, 1952). In these
cases the resulting distributional patterns are not
explainable through ecological correlates but rather
through striking geographical concordance with formerly unglaciated or only weakly glaciated regions
(e.g. Merxmüller, 1952, 1953, 1954; Schneeweiss &
Schönswetter, 1999). In the Alps these regions are in
good congruence with centres of endemism
(Pawlowski, 1970), e.g. the north-eastern (Niklfeld,
1972) and southern Calcareous (Pitschmann &
Reisigl, 1959) Alps.
Since the central Eastern Alps are flanked by
peripheral limestone ranges to the north and south,
only a few regions with siliceous bedrock were unglaciated or only locally glaciated during the maximum
extent of the Pleistocene ice shield (Van Husen, 1987).
By far the largest ice-free area was the easternmost
Central Alps. Furthermore, smaller ice-free areas
were situated in the Southern Alps in the south-
© 2003 The Linnean Society of London, Botanical Journal of the Linnean Society, 2003, 141, 437–446
437
438
P. SCHÖNSWETTER ET AL.
Figure 1. Distribution of Androsace brevis (squares and lined area around squares) and A. wulfeniana (circles and squared
areas). Filled symbols are sampled populations, the numbers refer to the population numbers given in Table 1. The
maximum extent of the ice-shield during the last glaciation period (Wuerm) in the Alps is given as a black line.
western Dolomites, southern Adamello, western Alpi
Bergamasche and adjacent Alpi Lepontine (Jäckli,
1970). These regions provided, if not entirely unglaciated territory, at least nunataks in a very peripheral
situation. Thus, judging from geological evidence
these regions are likely to have acted as Pleistocene
refugia for calcifuge alpine plants.
Modern DNA techniques are excellent tools to
reconstruct population histories. The level of genetic
differentiation gives insights, e.g. on the relative timing of splitting events and the relationships between
populations. This can be used to determine the origin
of disjunctions (recent long-distance dispersal vs. old
splitting event) as well as to reconstruct migration
patterns and to recognize refugial populations. The
genetic variability of populations can be used for
the detection of bottlenecks and the estimation of
viability.
A good model to investigate such questions is provided by the species pair Androsace wulfeniana Sieber
ex Koch and A. brevis (Hegetschw.) Cesati (Primu-
laceae), which are sister species according to preliminary phylogenetic data (DNA-sequencing and AFLPfingerprinting, G. M. Schneeweiss et al. unpubl.).
Androsace wulfeniana is distributed in the easternmost Central Alps of Austria and disjunct (260 km) in
the siliceous parts of the southern Dolomites in Italy
(Fig. 1). In contrast, A. brevis has a compact distributional area in the southern Alps around Lake Como in
Italy and nearby Switzerland (Fig. 1). All three
regions were either weakly glaciated or situated at the
periphery of the ice shield during the last glaciation
(Fig. 1). The habitat requirements of the two species
are very similar. Both are restricted to acidic to subneutral siliceous bedrock and grow on wind-exposed
ridges with low vegetation cover or on rocky outcrops,
between 2000 and 2600 m (Franz, 1988; Käsermann &
Moser, 1999). The high-alpine, colonizing A. alpina
(L.) Lam., which is distributed throughout the high
parts of the Alps, was recently investigated applying
the same methodology (P. Schönswetter, A. Tribsch &
H. Niklfeld, unpubl.). This allows a comparison of the
© 2003 The Linnean Society of London, Botanical Journal of the Linnean Society, 2003, 141, 437–446
PHYLOGEOGRAPHY OF ANDROSACE BREVIS AND A. WULFENIANA
439
Table. 1. Populations, location name (A: Austria, I: Italy), coordinates, altitude in m a.s.l. and estimated population size
[1: small (<100); 2: large (>100)] of the 16 investigated populations of Androsace wulfeniana (1–8) and A. brevis (9–16)
Population number
Location
Coordinates (E/N)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
A: Dreistecken
A: Gstoder
A: Gumma
A: Zirbitzkogel
A: Bretthöhe
A: Falkert
I: Cavallazza Piccola
I: Forcola di Coldose
I: Valle del Muretto
I: Rifugio Gianetti
I: Passo d’Oro
I: Cima Pianchette
I: Monte Azzarini
I: Monte Colombana
I: Monte Rotondo
I: Monte Legnone
14∞23¢
14∞13¢
13∞46¢
14∞34¢
13∞56¢
13∞49¢
11∞47¢
11∞37¢
09∞44¢
09∞35¢
09∞34¢
09∞08¢
09∞38¢
09∞30¢
09∞29¢
09∞25¢
genetic variability of the two rare relict taxa A. brevis
and A. wulfeniana with their widespread congener
A. alpina.
The following questions are addressed in this
study: are the populations of A. wulfeniana in the
Dolomites glacial survivors or did they originate
from rather recent long-distance dispersal? Is there
structure within the two disjunct distributional
areas of A. wulfeniana or the compact one of
A. brevis? Are there differences regarding genetic
diversity between the two species or the three regions,
respectively? Are there such differences between
the two investigated relict taxa and the more widespread high-alpine congener A. alpina, a colonizing
species?
MATERIAL AND METHODS
SAMPLING
Eight populations of A. wulfeniana and eight populations of A. brevis covering the entire distributional
ranges of the two species were sampled (Table 1,
Fig. 1). The population size was roughly estimated in
two categories (Table 1). Usually, leaf-material of five
individuals per population was collected. Due to
extremely small population sizes, in four populations
of A. brevis only material of one or two individuals was
collected. Young shoots (flowers and buds were
removed) were immediately stored in silica gel. Herbarium specimens of all sampled populations are
deposited in the herbarium of the Institute of Botany
of the University of Vienna (WU).
50¢¢ / 47∞27¢
00¢¢ / 47∞17¢
48¢¢ / 47∞12¢
07¢¢ / 47∞04¢
18¢¢ / 46∞54¢
16¢¢ / 46∞51¢
20¢¢ / 46∞17¢
34¢¢ / 46∞15¢
35¢¢ / 46∞20¢
35¢¢ / 46∞17¢
00¢¢ / 46∞15¢
50¢¢ / 46∞07¢
40¢¢ / 46∞03¢
20¢¢ / 46∞03¢
30¢¢ / 46∞04¢
00¢¢ / 46∞05¢
DNA
27¢¢
50¢¢
42¢¢
45¢¢
50¢¢
30¢¢
45¢¢
31¢¢
25¢¢
00¢¢
40¢¢
30¢¢
30¢¢
45¢¢
10¢¢
45¢¢
Altitude
Population size
2360
2240
2310
2225
2300
2020
2170
2180
2280
2540
2570
2140
2400
2355
2495
2600
2
2
1
1
2
1
1
2
1
1
1
1
1
1
1
2
ISOLATION AND
AFLP
FINGERPRINTING
In contrast to other congeners, e.g. A. alpina
(Schönswetter et al. unpubl.), DNA extraction was
problematic – apparently due to a high amount of
polysaccharides in the plants. The best quality of
extracts was obtained by a combination of different
protocols. Plant material was ground to a fine powder
with a shaking-mill (Retsch MM 200). Then 800 mL of
AP1 extraction buffer (Dneasy Plant Mini Kit, Qiagen)
were added and shaken on a thermoblock at 60 ∞C.
After 10 min 260 mL of AP2 precipitation buffer
(Dneasy Plant Mini Kit, Qiagen) were added. After
5 min on ice and subsequent centrifuging at
14 000 r.p.m. for 5 min the supernatant was moved to
a new Eppendorf tube and 500 mL chloroform/isoamylalcohol (24 : 1) were added. After mixing and standing
for 5 min it was centrifuged again and the aqueous
phase was moved to a new Eppendorf tube. 500 mL isopropanol were added and after standing for 5 min followed by centrifuging the supernatant was discarded.
1 ml 96% ethanol was added. After vigorous manual
shaking the extractions were put on a thermoblock
shaking at maximum speed at 37 ∞C. After c. 0.5 h the
pellet became isolated from a diffuse slime. If necessary, this step was repeated. The quality of the
extracted DNA was checked on 1% TAE-agarose gels.
The amount of DNA was estimated photometrically
(UV-160 A, Shimadzu).
Genomic DNA (c. 500 ng) was digested with MseI
(New England BioLabs) and EcoRI (Promega) and
ligated (T4 DNA-Ligase; Promega) to double-stranded
adapters and preamplified using the AFLP Ligation
© 2003 The Linnean Society of London, Botanical Journal of the Linnean Society, 2003, 141, 437–446
440
P. SCHÖNSWETTER ET AL.
and Preselective Amplification Module for regular
genomes following the manufacturer’s instructions
(PE Applied Biosystems, 1996). The incubation of the
restriction-ligation reactions (2 h at 37 ∞C) as well as
the PCRs were performed on a GeneAmp PCR System 9700 thermal cycler. Deviating from the manufacturer’s instructions, the PCRs were run in a
reaction volume of 5 mL. Three primer combinations,
which were used for the closely related A. alpina
(Schönswetter et al. unpubl.) gave clear, easily and
unambiguously scoreable results (EcoRI FAM-ACA-MseI
CAT; EcoRI JOE-AAG-MseI CTG; EcoRI NEDAAC-MseI CTT). On some samples independent
AFLP-reactions were performed for internal control.
The fluorescence-labelled selective amplificationproducts were separated on a 5% polyacrylamide gel
with an internal size standard (GeneScan-500 [ROX],
PE Applied Biosystems) on an automated sequencer
(ABI 377). Raw data were collected and aligned with
the internal size standard using the ABI Prism
GeneScan Analysis Software (PE Applied Biosystems). Subsequently, the GeneScan-files were imported into Genographer (version 1.1.0, © Montana State
University, 1998; http://hordeum.msu.montana.edu/
genographer/) for scoring of the fragments. Each
AFLP-fragment was scored using the thumbnail option of the program which allows comparison of the
signal per locus over all samples. The few AFLPfragments that exhibited ambiguous peaks were excluded from the analysis. Peaks of low intensity were
included in the analysis when an unambiguous scoring was possible. The results of the scoring were
exported as a presence/absence matrix and used for
further manipulation.
DATA
RESULTS
AFLP-PATTERNS
AND POLYMORPHISM
With the three primer combinations used, 205 unambiguously scoreable fragments were generated.
Thirty-six fragments (17.6%) are monomorphic in the
entire data set. In A. brevis 33 (28.4%) of 116 fragments were polymorphic, in A. wulfeniana 119 (69.6%)
of 171. The number of AFLP-fragments per individual
varied from 96 to 104 in A. brevis and from 97 to 112
in A. wulfeniana.
WITHIN-POPULATION
VARIATION (TABLE
2)
Six pairs of individuals with identical AFLP profiles
were detected. Four were found in A. brevis (within
pop. 11 and pop. 14, between pop. 12 and pop. 9,
between pop. 14 and pop. 15), and two in
A. wulfeniana from the Dolomites (within pop. 7 and
pop. 8). HSh ranged from 2.57 to 4.98 with an average
of 3.39 in A. brevis, and from 1.4 to 14.2 with an average of 8.99 in A. wulfeniana. Excluding pops. 7 and 8
from the Dolomites (average 2.01), the average for the
main distribution area is 11.29. Boxplots of HSh of
A. brevis, A. wulfeniana and A. alpina (data from
Schönswetter et al. unpubl.) are given in Figure 2. HSh
of A. alpina and A. wulfeniana excluding pops. 7 and 8
ANALYSIS
Shannon Diversity index H Sh = -S(pi ln pi), where pi is
the relative frequency of the ith fragment (Legendre &
Legendre, 1998) and the mean Jaccard similarities
between and within populations were calculated. The
number of variable fragments and the numbers of private (i.e. confined to a single population) and fixed private (i.e. found in all investigated individuals of a
single population) fragments were estimated. All these
parameters were determined only for populations with
four or five investigated individuals. Hence, four populations (pops. 9–12) of A. brevis were omitted. Analyses
of molecular variance (AMOVAs) were calculated with
Arlequin 1.1 (Schneider et al., 1997). A neighbourjoining tree of all individuals based on the distance
measure by Nei & Li (1979) was constructed with
Treecon 1.3b (Van de Peer & De Wachter, 1994). A Principal Coordinate Analysis (PCoA) based on a matrix of
between-individual Jaccard similarities and boxplots
of HSh were calculated and plotted with SPSS 8.0.
Figure 2. Comparison of Shannon Diversity Indices of
Androsace alpina, A. brevis, A. wulfeniana in the Dolomites and A. wulfeniana in the eastern Central Alps. Boxplot: the box represents the interquartile range which
contains 50% of the values and the median (horizontal line
across the box); the whiskers are lines that extend from the
box to the highest and lowest values, excluding outliers ().
© 2003 The Linnean Society of London, Botanical Journal of the Linnean Society, 2003, 141, 437–446
PHYLOGEOGRAPHY OF ANDROSACE BREVIS AND A. WULFENIANA
441
Table 2. Genetic variation in the 16 investigated populations of Androsace wulfeniana and A. brevis. N: number of
individuals which were included in the analyses; HSH: Shannon Diversity Index; NPF (NFPF): number of private fragments
(number of fixed private fragments); PPOLY: percentage of variable fragments
Population number
Location
N
HSH
NPF (NFPF)
PPOLY
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Dreistecken
Gstoder
Gumma
Zirbitzkogel
Bretthöhe
Falkert
Cavallazza Piccola
Forcoladi Coldose
Valledel Muretto
Rifugio Gianetti
Passod’ Oro
Cima Pianchette
Monte Azzarini
Monte Colombana
Monte Rotondo
Monte Legnone
5
4
5
5
4
4
5
5
1
1
2
2
5
5
5
5
14.22
9.39
10.10
9.52
13.68
10.82
1.40
2.73
–
–
–
–
4.98
2.57
3.39
2.62
4(1)
1
0
6(2)
2
0
2(2)
5(4)
–
–
–
–
0
0
0
2
38.9
27.4
29.2
28.1
33.1
27.7
5.9
8.3
–
–
–
–
15.6
7.8
11.5
8.6
are not significantly different (t-test, P < 0.01). Significant differences were found between A. brevis and
A. alpina and A. wulfeniana (excluding pops. 7 and 8).
The percentage of variable loci ranged from 7.8 to 15.6
in populations of A. brevis and from 5.9 to 38.9 in
A. wulfeniana. Private fragments (1–4 per population)
were found in one population of A. brevis and five of
A. wulfeniana. Fixed private fragments were only
detected in A. wulfeniana in pop. 4 (2 fixed private
fragments), pop. 1 (1), pop. 7 (2) and pop. 8 (4).
BETWEEN-POPULATION
VARIATION
The neighbour-joining tree (Fig. 3) of the individuals
shows no geographical structuring at all in A. brevis,
but a very high one in A. wulfeniana, where three geographical regions are clearly separated: (a) Zirbitzkogel (pop. 4) and eastern Niedere Tauern (pops. 1, 2); (b)
Gurktaler Alpen (pops. 5, 6) and western Niedere
Tauern (pop. 3); and (c) Dolomites (pops. 7, 8). This difference between the two species is also reflected by the
analyses of molecular variance (AMOVA, Table 3). The
proportion of the total genetic variation assigned to
variation between populations is four times higher in
A. wulfeniana than in A. brevis. If in A. wulfeniana a
geographical structure (i.e. the three groups listed
above) is added as a third level of variation, 35.6% is
assigned to variation among those groups. If only the
main distributional area in the easternmost Central
Alps is considered, the value decreases to 18.1%.
Because of the vicinity of A. brevis populations repre-
Figure 3. Neighbour-joining tree of Androsace brevis (left)
and A. wulfeniana (right); the numbers refer to populations
listed in Table 1. Scale bar = 10% genetic distance (Nei &
Li, 1979).
© 2003 The Linnean Society of London, Botanical Journal of the Linnean Society, 2003, 141, 437–446
442
P. SCHÖNSWETTER ET AL.
Table 3. Results of the AMOVAs (Analyses of Molecular Variance). (a), (b) Partitioning of the overall genetic variation on
two levels (within and between populations). (c)–(e) Level of variation between groups added. (c) Grouping with highest
value for variation between groups (pop. 13, pop. 16) (pop. 14, pop. 15). (d) Grouping according to PCoA and neighbourjoining (pop. 1, pop. 2, pop. 4) (pop. 3, pop. 5, pop. 6) (pop. 7, pop. 8). (e) Populations from the Dolomites (pop. 7, pop. 8)
excluded. d.f., degrees of freedom; MS, mean sum of squares; *P < 0.001. Significance levels are based on 1023 permutations. (f) For comparison, values of the widespread congener A. alpina taken from Schönswetter et al. (unpubl.)
(a) A. brevis
(b) A. wulfeniana
(c) A. brevis
(d) A. wulfeniana
(e) A. wulfeniana
(excl. Dolomites)
(f) A. alpina
Source of variation
d.f.
MS
Variance components
Percentage of
variation accounted for
among populations
within populations
among populations
within populations
among groups
among populations
within populations
among groups
among populations
within populations
among groups
among populations
within populations
among populations
within populations
3
16
7
29
1
2
16
2
5
29
1
4
21
52
204
16.00
46.40
438.53
223.25
6.80
9.20
46.40
259.69
178.84
223.25
80.45
136.74
209.25
1843.75
1744.15
0.49
2.90
11.90
7.70
0.22
0.34
2.90
7.63
6.13
7.70
3.40
5.41
9.96
5.55
8.55
14.37
85.63
60.72
39.28
6.36
9.83
83.82
35.57
28.56
35.87
18.13
28.82
53.06
39.36
60.64
Fst
0.144
0.607*
0.162*
0.641*
0.469*
0.394*
Table 4. Mean Jaccard distances within and between pairs of populations of Androsace wulfeniana and A. brevis
wulfeniana
pop. 1
pop. 2
pop. 3
pop. 4
pop. 5
pop. 6
pop. 7
pop. 8
pop. 1
0.213
pop. 2
0.278
0.163
pop. 3
0.321
0.313
0.151
pop. 4
0.299
0.312
0.312
0.150
brevis
pop. 13
pop. 14
pop. 15
pop. 16
pop. 13
0.08
pop. 14
0.09
0.05
pop. 15
0.09
0.05
0.06
pop. 16
0.08
0.04
0.05
0.04
sented with a sufficient number of individuals in the
data set, and due to the obvious lack of geographical
structure in the neighbour-joining tree, the introduction of a third level of variance is not meaningful in
this species. However, to enable a comparison with
A. alpina and A. wulfeniana AMOVAs for all possible
groupings of populations of A. brevis were calculated.
The highest values for variation between groups were
obtained for a grouping of pops. 13 and 16 vs. pops. 14
and 15 with 6.4% for variation between groups.
pop. 5
0.319
0.300
0.224
0.318
0.217
pop. 6
0.311
0.276
0.218
0.299
0.219
0.173
pop. 7
0.400
0.390
0.303
0.407
0.328
0.322
0.026
pop. 8
0.417
0.372
0.345
0.419
0.355
0.322
0.177
0.042
A clear difference between the two species is found
in mean Jaccard distances between pairs of populations (Table 4). The mean is 0.07 for A. brevis and 0.32
for A. wulfeniana. If the disjunct populations from the
Dolomites are excluded, the value decreases to 0.29.
A Principal Coordinate Analysis (PCoA) calculated
for A. wulfeniana visualizes the drastic differences
between the three geographical groups (explanation of
the total variance: 1st factor 31.4%, 2nd factor 27.6%,
3rd factor 22.5%; Fig. 4). The populations from the
© 2003 The Linnean Society of London, Botanical Journal of the Linnean Society, 2003, 141, 437–446
PHYLOGEOGRAPHY OF ANDROSACE BREVIS AND A. WULFENIANA
Figure 4. Principal Coordinate Analysis (PCoA) of all
investigated individuals of Androsace wulfeniana. The two
axes explain 70.8% (factor 1) and 7.6% (factor 2) of the
overall variation. Squares, Dolomites; triangles, Gurktaler
Alpen and western Niedere Tauern; circles, Zirbitzkogel
and eastern Niedere Tauern; numbers refer to populations
listed in Table 1.
Dolomites (pop. 7, pop. 8) are clearly separated from
all other populations, but within the main distribution
area in the easternmost Alps there is a pronounced
differentiation in a western (pop. 3, pop. 5, pop. 6) and
an eastern (pop. 1, pop. 2, pop. 4) group.
DISCUSSION
As outlined above, the three geographical entities of
Androsace brevis, A. wulfeniana in its main distributional area in the eastern Central Alps, and
A. wulfeniana in the south-western Dolomites, differ
remarkably regarding the level of genetic variation
and its structure.
The current ecological conditions allow no explanation for these differences. Population sizes as well as
autecological aspects are very similar in A. brevis and
A. wulfeniana: both species are nearly identical in
their habitat requirements. Furthermore, in both species very large populations with hundreds of individuals (A. brevis: pop. 16; A. wulfeniana: pop. 5) as well
as very small ones (A. brevis: pops. 4 and 7;
A. wulfeniana: pops. 13 and 14) were investigated.
According to the very sparse statements given in literature, both species are outbreeders (Lüdi, 1927). In
the related high-alpine A. alpina a pollen/ovule ratio
ranging between facultative xenogamy and xenogamy
(Cruden, 1977) combined with high self-compatibility
was found (Schönswetter et al. unpubl.). Hence, expla-
443
nations need to be sought in the histories of the
populations.
Androsace brevis exhibits low genetic variation and
lacks any geographical structuring. The largest population known to the authors (pop. 16) is less genetically variable than the very small population of
A. wulfeniana on Zirbitzkogel in the eastern Central
Alps (pop. 4). Individuals with identical AFLP profiles
were not only found within populations (as in
A. wulfeniana in the Dolomites), but also c. 70 km
apart. These data suggest that this species survived
the Pleistocene glaciation in one (or perhaps more)
strongly bottlenecked population in a single refugium.
From there, it subsequently (re)colonized the currently occupied distributional area.
Androsace wulfeniana in the Dolomites is genetically differentiated from A. wulfeniana in the eastern
Central Alps on a high level and possesses several
fixed private alleles. Recent phylogeographical AFLP
studies on alpine plants (Schönswetter et al., 2002;
Tribsch, Schönswetter & Stuessy, 2002) demonstrate
that descendants of relatively recent long-distance
dispersals are characterized by extremely low genetic
variation in combination with a lack of genetic differentiation (e.g. no private fragments). Thus we suggest
that the populations in the Dolomites are not a result
of recent long-distance dispersal but descendants of
glacial survivors. Although the genetic variation of
A. wulfeniana in the Dolomites is even lower than that
of A. brevis, the two populations investigated are
clearly separated from each other and each possesses
fixed private alleles. This points to in situ survival of
(at least) two spatially isolated populations trapped
between ice to the north and below 1400 m above sea
level (a.s.l.) (Van Husen, 1987) and a limestone barrier
to the south. A postglacial range expansion, if it
occurred, was obviously very limited.
The highest genetic variation is exhibited by
A. wulfeniana in the eastern Central Alps. Although
some of the populations investigated are very small
(e.g. pop. 4), no individuals with identical AFLP patterns were found. Apart from pops. 5 and 6 from the
Gurktaler Alpen, which is the current centre of frequency of A. wulfeniana (Fig. 5), all populations are
clearly separated from each other. The populations of
the western Niedere Tauern (pop. 3) are more similar
to those of the Gurktaler Alpen (pops. 5 and 6) to the
south, than to those in the eastern Niedere Tauern
(pops. 1 and 2). We propose therefore a postglacial
recolonization of the western Niedere Tauern from a
refugium in the unglaciated Gurktaler Alpen (Fig. 5).
The easternmost population of A. wulfeniana in the
eastern Niedere Tauern (pop. 1) and on Zirbitzkogel
(pop. 4) are possibly remnants of refugial populations
as indicated by the high number of private and fixed
private fragments (Table 2). They have probably been
© 2003 The Linnean Society of London, Botanical Journal of the Linnean Society, 2003, 141, 437–446
444
P. SCHÖNSWETTER ET AL.
Figure 5. Distributional area of Androsace wulfeniana
(circles) in the eastern Central Alps and the maximum
extent of the ice-shield during the last Pleistocene glaciation period (Wuerm; redrawn from Fink & Nagl, 1979).
White, glaciated area; grey, unglaciated areas and nunataks. Insert: position of mapped area in Austria. Arrow
indicates the direction of recolonization of the western
Niedere Tauern from a refugial area in the Gurktaler
Alpen.
reduced to their present very small population sizes in
rather recent times, and therefore still exhibit relatively high genetic variability.
The two refugia in the Southern Alps, which supported A. wulfeniana in the Dolomites and A. brevis,
and the refugium in the eastern Central Alps, differ
regarding the intensity of Pleistocene glaciation
(Jäckli, 1970; Van Husen, 1987). The eastern Central
Alps provided, due to their position on the eastern border of the continuous ice-shield (Fig. 1), vast unglaciated areas of siliceous bedrock. The siliceous part of
Alpi Bergamasche and the southern Dolomites, however, were situated within the ice-shield (Fig. 1), albeit
close to its southern margin. Even though the upper
surface of the glaciers was relatively low in this area
(c. 1100–1400 m a.s.l.; Jäckli, 1970; Van Husen, 1987),
conditions were certainly harsh in these comparatively small areas. Although the distinctness of
A. wulfeniana in the Dolomites can be regarded as a
strong hint for nunatak-survival in the south-western
Dolomites, it should be interpreted with caution. Considering the notion of ‘nunataks’ as ice-free mountain
tops protruding from an ice shield, this term could certainly be applied to the mode of glacial survival
A. brevis and A. wulfeniana in the Dolomites most
possibly have experienced. Misleadingly, the term
‘nunatak survivors’ is usually only used for populations surviving on the highest, most extensively glaciated mountains in the very central parts of the Alps
(e.g. Stehlik, Schneller & Bachmann, 2001). In order
not to be confused with this controversial phenomenon
(reviewed in Stehlik, 2000), we propose this type of
less spectacular, but probably much more important,
survival more precisely as ‘survival on peripheral
nunataks’.
The heterogeneity within the formerly unglaciated
eastern Central Alps is reflected by irregularities in
distributional patterns of many relict vascular plant
species (Schneeweiss & Schönswetter, 1999). An interesting example already analysed with molecular techniques is provided by Cochlearia excelsa (Koch, 2002).
It is an endemic species of the easternmost Central
Alps and only known from two populations in the eastern Niedere Tauern and the Gurktaler Alpen. Enzyme
analysis revealed that the populations are differentiated by some private alleles detected in the one from
Niedere Tauern, indicating long-term isolation. Thus,
this taxon is a well-investigated parallel case to Androsace wulfeniana, indicating an ancient split in at
least two separate refugia within the easternmost siliceous parts of the Alps.
COMPARISON OF THE TWO RELICTUAL SPECIES
ANDROSACE BREVIS AND A. WULFENIANA WITH THE
PIONEER SPECIES A. ALPINA
Androsace alpina is a high alpine to subnival pioneer
species endemic to the Alps, where it is widespread
and often frequent at higher elevations. A phylogeographical analysis of this taxon has recently been
undertaken by Schönswetter et al. (unpubl.). In contrast to A. wulfeniana and A. brevis, which occur in
stable habitats, A. alpina often occurs in pioneer
assemblages. Accordingly, different strategies and
population dynamics and corresponding differences in
HSh can be expected. Androsace brevis exhibits generally less intrapopulational genetic variation than
A. alpina (Fig. 2). Androsace wulfeniana in the eastern Central Alps, however, exhibits levels of genetic
variation similar to A. alpina (Fig. 2). In contrast, the
populations of A. wulfeniana in the Dolomites are the
least polymorphic in the data set (Fig. 2). The partitioning of the total variation to within population and
among population variation of A. alpina is intermediate between A. brevis and A. wulfeniana (Table 3).
These results contradict the hypothesis that species
with small ranges generally exhibit lower genetic variation than widespread ones (Hamrick, Linhart &
Mitton, 1979; Hamrick & Godt, 1989). Loveless &
Hamrick (1984), however, argue, that due to the influence of historical factors and habitat heterogeneity,
© 2003 The Linnean Society of London, Botanical Journal of the Linnean Society, 2003, 141, 437–446
PHYLOGEOGRAPHY OF ANDROSACE BREVIS AND A. WULFENIANA
geographical range is not a good predictor of genetic
structure. In a recent review, Gitzendanner & Soltis
(2001) found significant, but small, differences in most
diversity indices between rare plants and widespread
species. Furthermore, the high level of genetic variation in A. wulfeniana allows rejection of the assumption that relict species were not able to extend their
distributional area due to genetic depauperation (e.g.
Stebbins, 1942). However, in some studies it has been
demonstrated that rare species can be as polymorphic,
or even more polymorphic, than their widespread congeners (Vogelmann & Gastony, 1987; Ranker, 1994;
Young & Brown, 1996).
The high level of genetic variation in the main distributional area of A. wulfeniana indicates the need to
search for other causes of the rarity of the species.
Autecological requirements, however, do not give any
hints as there are no apparent differences either in the
floral syndrome or in seed shape or size in A. alpina,
which has colonized vast areas of the Alps after the ice
age. The types of bedrock to which A. wulfeniana is
restricted, as well as its preferred habitats, are widespread and common in the Alps. Furthermore, the species, similar to A. alpina, is apparently a weak
competitor and always restricted to microsites with
very low vegetation cover. As a consequence,
changes in patterns of interspecific competition due to
climatic changes or the arrival of new immigrating
taxa in the course of floristic exchange during the
Pleistocene is likely to have had only minor effect on
A. wulfeniana.
The situation in the three species of Androsace discussed here shows clearly that the interpretation of
the phenomenon ‘rarity’ must take into account the
history of the investigated taxa and the ecological factors leading to their present-day restriction.
ACKNOWLEDGEMENTS
Funding by the Austrian Science Foundation (FWF,
P13874-Bio) is gratefully acknowledged. Thanks go to
all the people who accompanied us in the field or collected samples for us (Karl Hülber, Sonja Latzin,
Luise Schratt-Ehrendorfer, Corinna Schmiderer,
Erich Sinn, Magdalena Wiedermann, Manuela Winkler). We are indebted to Tod F. Stuessy and an anonymous reviewer for very helpful comments on the
manuscript and correcting our English. Thanks
also to Michael Barfuß for technical assistance in the
laboratory.
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