Primulaceae) in the European Alps

Original Paper 623 Phylogeography of the High Alpine Cushion Plant Androsace alpina (Primulaceae) in the European Alps P. Schönswetter1, A. Tribsch2, and H. Niklfeld1 1 Department of Plant Chorology and Vegetation Science, Institute of Botany, University of Vienna, Vienna, Austria 2 Department of Systematics and Evolution of Higher Plants, Institute of Botany, University of Vienna, Rennweg14, 1030 Vienna, Austria Received: January 31, 2003; Accepted: November 11, 2003 Abstract: Recent studies elucidating the glacial history of alpine the centre of the Pleistocene ice shields covering the Alps and plants have yielded controversial results. While some have fav- Scandinavia also harbour such taxa. The nunatak hypothesis, oured glacial survival on mountain tops above the glaciers claiming that plants could survive on mountain tops protrud- (nunataks), others did not find support for this hypothesis. Fur- ing from the ice shield (reviewed in Dahl, 1987), was formulat- thermore, all of the published phylogeographic patterns are ed to explain this pattern. The alternative tabula rasa (latin for strikingly different. In order to provide more data for a future ªempty tableº) hypothesis argues for sole periglacial survival comparative phylogeographical approach, we investigated 53 (reviewed in Nordal, 1987; Birks, 1993). populations of the high alpine cushion plant Androsace alpina (Primulaceae), endemic to the European Alps, using amplified Whereas many contributions exist toward understanding gla- fragment length polymorphism (AFLP). While Principal Co-ordi- cial survival of tree species in southern European refugia (re- nate Analysis (PCoA) of populations revealed four genetically- viewed by, e.g., Taberlet et al., 1998; Newton et al., 1999; defined phylogeographical groups corresponding to geographic Comes and Kadereit, 2001), arctic and alpine plants have been regions, Neighbour Joining analysis (NJ) separated only three neglected until recently. A series of studies dealing with arctic groups. Mantel tests were used to assess the goodness-of-fit be- taxa (Brochmann et al., 1996; Gabrielsen et al., 1997; Tollefsrud tween the grouping in PCoA and the genetic similarity matrix, et al., 1998) found no evidence for the nunatak hypothesis, and and these showed high similarity between the two eastern phy- it was thus concluded that ªglacial survival does not matterº logeographical groups. This, together with other lines of evi- (Gabrielsen et al., 1997; Tollefsrud et al., 1998). Only in the dence, is interpreted as an indication for colonization of the last few years have alpine plants become the focus of inter- eastern part of the distributional range of A. alpina from wester- est (Stehlik et al., 2001a, b, 2002a, b; Stehlik, 2002; Holder- ly adjacent populations. The phylogeographical groups can all egger et al., 2002; Kropf et al., 2002, 2003; Schönswetter et be related to potential refugia for alpine plants, based on geo- al., 2002, 2003, in press; Tribsch et al., 2002). Stehlik et al. logical and palaeoclimatological data. However, due to the com- (2001a; 2002 b) provided evidence for nunatak survival in the paratively weak phylogeographical structure, our data do not centralmost parts of the Alps for the high alpine Eritrichum allow us to rule out glacial survival on nunataks in central parts nanum. Even in the low alpine Erinus alpinus (Stehlik et al., of the Pleistocene ice shield. 2002 a), glacial survival on nunataks in the northern Swiss Alps may account for its present phylogeographic pattern. Key words: AFLP, Androsace alpina, glacial survival, nunatak, However, results from Phyteuma globulariifolium (Schönswet- phylogeography, Pleistocene. ter et al., 2002), and Ranunculus glacialis (Schönswetter et al., in press), which have an altitudinal distribution similar to E. nanum, favour survival in unglaciated refugia and peripheral nunatak areas close to the southern and eastern margin of the Introduction Alps. Peripheral nunataks were situated close to the margin of the ice shield and provided potential habitats below the Pleis- Where did plants growing at high altitudes in mountain ranges tocene snow line (Schönswetter et al., 2002, in press). In con- like the European Alps survive the glaciations of the Pleisto- trast, central nunataks were restricted to interior parts of the cene? This question has been addressed by biogeographers ice shield. The classical nunatak debate traditionally only dis- many times (reviewed in Brockmann-Jerosch and Brock- tinguished unglaciated refugia and central nunataks (Stehlik, mann-Jerosch, 1926; Stehlik, 2000). It was observed that the 2000); peripheral nunataks, however, obviously offered condi- distribution of ªglacial relicsº (i.e., rare, disjunct, or palaeoen- tions more suitable for growth and survival of higher plants. demic taxa) is not confined to areas that remained ice-free during the last glaciation, but rather that mountain ranges in The general aim of the present study was to provide detailed phylogeographic data from an exclusively high alpine to subni- val plant, to test further the still controversial nunatak hypoth- Plant Biology 5 (2003): 623 ±630 esis. Our objectives were (1) to attempt to identify Pleistocene Georg Thieme Verlag Stuttgart ´ New York refugia by comparing the phylogeographic pattern with poten- ISSN 1435-8603 ´ DOI 10.1055/s-2003-44686 tial refugia described in Schönswetter et al. (2002), and (2) to 624 Plant Biology 5 (2003) P. Schönswetter, A. Tribsch, and H. Niklfeld Fig.1 Distribution of Androsace alpina (shad- ed) and sampled populations (numbered, see Table 1) in the Alps. Groupings based on genetic results are indicated by the following symbols: rhombi = SW, squares = W, trian- gles = E1, dots = E2. The maximum extent of the Pleistocene ice shield duringthe last glacial period (Würm) is illustrated with a black line (modified from van Husen, 1987; Jäckli, 1970; and Voges, 1995). distinguish between peripheral survival and survival on cen- Materials and Methods tral nunataks. Nunatak survivors, if not completely swamped by re-migrating genotypes (Gabrielsen et al., 1997; Tollefsrud The species et al., 1998; Holderegger et al., 2002), should exhibit a patchy distribution of groups of related genotypes in formerly glaciat- Androsace alpina is a typical alpine pioneer species with appar- ed central areas of the Alps. These groups should be potentially ently low competitive abilities, as it is strictly bound to open differentiated from and surrounded by peripheral genotypes. vegetation (P. Schönswetter, pers. obs.). In many aspects, it is An example for this kind of glacial survival in the western similar to high alpine Ranunculus glacialis, that Grabherr et al. central Alps is provided by Stehlik et al. (2002 b). In contrast, (1986) regarded as ªalpine ruderalº. The population size of A. one would expect re-migration of (now mostly extinct) refu- alpina varies considerably, from small populations on summits gial populations from peripheral refugia to result in large, rel- and ridges with fewer than ten individuals to very large popu- atively uniform areas populated by closely related genotypes lations, e.g. in glacier forefields, with thousands of plants (P. (Schönswetter et al., 2002, in press). Schönswetter, pers. obs.). This is also reflected by the sampled populations (Table 1). A pollen/ovule-ratio of 1600±1800 (H. Androsace alpina (Primulaceae) belongs to the three highest- Weiss, unpubl.) for the southwesternmost population 1 and dwelling vascular plant taxa in the European Alps, frequently population 46 near the eastern distribution limit (Fig.1) sug- growing at or even above the snow line (at ca. 3000 m asl) gests (facultative) xenogamy (Cruden, 1977). Androsace alpina and sometimes reaching 4200 m asl (Ellenberg, 1996). The is also highly self-compatible, as seed set does not differ signif- species is endemic to the Alps (Fig.1). It is most frequent in icantly between plants packed in silk bags to prevent xenoga- the highest, most central parts (Mt. Blanc to Hohe Tauern), be- my and open-pollinated individuals used as reference (Schöns- coming rarer towards the southwest and the east. Judging by wetter, unpublished data; t-test, p = 0.154). The size of the its present habitat preferences, A. alpina hypothetically would seeds varies from 1.5 to 2.2 mm, their specific weight is > 1 have been able to survive the hostile conditions on nunataks (Müller-Schneider, 1986), and they lack morphological adapta- within the Pleistocene ice shield. This, together with its re- tions for dispersal over longer distances. striction to siliceous bedrock, makes A. alpina a good model or- ganism to test hypotheses on glacial refugia. Due to the geolo- Sampling gy of the Alps, with a central siliceous core flanked by peripheral limestone ranges over long distances, there are only a few Fifty-three populations (Table 1) throughout the distributional well circumscribed potential peripheral refugia providing sili- area of A. alpina were sampled, with five individuals in each ceous bedrock which was unglaciated, or at least situated be- population (exceptions: populations 13, 31, 49, and 52 with low the Pleistocene snowline (Schönswetter et al., 2002). Gla- four and 47 and 50 with three individuals). Voucher specimens cial survival of A. alpina in the Po plain near presumed refugia of all sampled populations are deposited in the herbarium of was improbable, as it was covered by boreal forests and steppe the Institute of Botany of the University of Vienna (WU).

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