Biogeography, genetic and fitness patterns of steppe plants

Intraspecific genetic diversity of species varies within their distributional ranges. According to the Central- Marginal Model, populations at the periphery are predicted to be genetically (and phenotypically) less diverse than populations near the centre. This phenomenon is often correlated with reduced population sizes/densities and higher population dynamics in peripheral regions, and might be the result of reduced success in reproduction, seed development, germination, and/or plant recruitment due to unfavourable environmental conditions. Otherwise, "marginal" (e.g. stressful) conditions characterising peripheral habitats might promote the development of evolutionary novelties (i.e. local adaptation, peripheral speciation), and theses habitats are therefore often of outstanding importance for the long-term persistence and evolution of species. It is the aim of the present project to study genetic diversity and plant performance patterns along a transect from more central to marginal sites by comparing several plant species likely sharing a common history as steppe plants. I selected four species at their (north)westernmost distribution limit in Europe (i.e. Carex supina, Inula germanica, Oxytropis pilosa, and Poa badensis) and three geographical regions representing a central-marginal transect from Hungary in the southeast to Austria (intermediate), and further to the (north)westernmost periphery in western Germany. At first, the biogeographical history will be illuminated using molecular methods (AFLPs, cpDNA- RFLPs). These analyses will uncover biogeographical patterns and will basically answer the question of predominant (successive) vicariance. Moreover, AFLP data will be utilised to date such a biogeographical scenario. I expect a strong differentiation among regions, and additionally, among populations due to postglacial (or even older) fragmentation and isolation of populations. Populations representing the westernmost region in Germany might be genetically more isolated from Hungarian populations than from the intermediate Austrian localities; i.e. representing intraspecific "successive vicariance". Furthermore, I assume a decline of the within-population genetic diversity following the central-marginal transect. This hypothesis will be tested by the comparison of both molecular markers and of the four study taxa representing animal- and wind-pollination. With respect to different pollination systems, I may assume the signal of among population differentiation to be more pronounced within the latter species group. Basically, intraspecific genetic diversities will be correlated with measures of individual/population abundances to extract general patterns of steppe plant diversity within a temporally (AFLP dating; see above) and spatially well- defined biogeographical European framework. Last but not least, DNA content/ploidy levels as well as the performance of steppe plant taxa representing the central-marginal transect will be investigated in terms of seed set/weight. Furthermore, a common garden competition experiment (Oxytropis, Poa) will be conducted to get insights into potential evolutionary changes. In this respect, AFLP patterns will also be screened for AFLP fragments possibly under selection using a FST -based genome scan approach.

Continental and Pannonian steppe plants are at their absolute westernmost distribution limit in Central Europe. Consequentially, these species are rare there and of high nature conservation priority. In the present biogeographical project a number of steppe taxa were studied comparatively along a transect crossing their distributional periphery. We used a fixed sampling scheme: for each species four populations were included representing three study regions the Pannonian region in Central Hungary, the range edge of the continuous Pannonian distribution in eastern Austria, and the isolated exclave at their absolute westernmost range limit in (south-)western Germany.We investigated Carex supina (Cyperaceae), Oxytropis pilosa (Fabaceae), and Poa badensis (Poaceae) by compiling genetic and fitness data; in addition, we analysed one or the other group of parameters for Adonis vernalis (Ranunculaceae), Bassia prostrata (Amaranthaceae), Inula germanica (Asteraceae), and Linum flavum (Linaceae). For genetic studies, we performed AFLP fingerprint analyses and cpDNA sequencing. As fitness parameters number of seeds/fruits, their weight, germination rates and for P. badensis also adult growth rates were surveyed. Using flow cytometry chromosomal differences were tested.The study of various fitness parameters showed variable results across steppe species: While clonal taxa, like C. supina and I. germanica, were generally characterised by low reproductive output and extremely low germination rates indicating no gradient along the study transect, O. pilosa was characterised by high fitness (particularly, high germination rates) at the absolute range limit, which is opposite to the hypothesised pattern. Germination rates in P. badensis were not significantly different among regions; however, flow cytometry revealed chromosomal differences between the westernmost exclave and populations from the other peripheral regions.Genetic analyses based on AFLPs mainly revealed vicariance patterns, which is also indicated by cpDNA variation within L. flavum. In O. pilosa, cpDNA haplotypes were predominantly not arranged geographically, while this genetic marker was almost invariable in C. supina and P. badensis. Based on AFLP data, C. supina showed for instance expected higher population differentiation in the westernmost exclave, but simultaneously no reduced genetic diversity. Therefore, patterns observed illustrate an overall heterogeneous picture with respect to both, fitness and genetic, data. Anyway, the results do mainly not follow the assumed biogeographical gradient across the peripheral transect, but rather represent species-specific postglacial vicariance histories. For several species, the high nature conservation significance of populations at their Central European range limit is supported.