Origin of steppe flora and fauna in inner-Alpine dry valleys

Large portions of the Earth`s surface are covered by steppes. Highly insular steppe areas are situated in interior parts of large mountain chains such as the European Alps. The steppes of the inner-Alpine valleys and the Eurasian steppes have many animal and plant species in common. Most of these are distributed continuously from Central Asia to Eastern Europe, but are restricted to the most continental areas in Western and Central Europe. This implies that the present disjoint patches of steppe vegetation did not develop independently, but rather were interconnected in former times. Migration patterns on a regional scale, such as within the Alps, are much less evident. It is not clear if the steppe biota in the inner-Alpine dry valleys are true relicts, restricted to areas with unfavourable conditions by the postglacial reforestation, or if dispersal among the dry valleys played a major role as well. There is rich knowledge about the past range dynamics of many alpine and subnival plants and animals. This is in stark contrast to the virtual absence of information on the immigration history of steppe elements in the Alps. We will explore the origin and diversification of the Alpine steppe flora and fauna by testing explicit hypotheses. In doing so, we will apply brand-new approaches taking advantage of next-generation sequencing (i.e., Restriction site associated DNA sequencing) to a representative array of characteristic taxa (four species of vascular plants, one grasshopper, one ant and one spider) sampled throughout most of their distribution ranges. Data will be evaluated using traditional and new, highly sophisticated approaches such as Approximate Bayesian Computation and interpreted in the light of palaeovegetational evidence. The following topics will be tackled in this project: (1) Did the steppe biota colonise each Alpine dry valley independently or is there evidence for genetic exchange among the insular steppe habitats of different valleys? (2) What are the biogeographic connections of steppe biota from the Alpine dry valleys with other areas of steppe vegetation in Eurasia? (3) Are phylogeographic patterns seen in steppe plants and animals congruent, implying range shifts of entire communities or rather idiosyncratic suggesting individualistic responses to climatic oscillations? (4) Our phylogeographic approach will unravel intraspecific patterns of spatial differentiation and temporal diversification across steppe plant and animal lineages. These will then not only be compared to each other, but also to independent data sources. Changes of distribution ranges of our study taxa through time will be hindcasted using environmental niche modelling. Finally, we aim to synthesize our results gained from the molecular investigations with palaeoecological evidence to provide a complete picture of the history of the steppe vegetation in and around the Alps during the Pleistocene and the Holocene.

Extrazonal steppes include those in inner-Alpine, continental valleys and adjacent areas, for instance the western Balkan Peninsula, and cover a relatively small area. In contrast, the zonal Eurasian steppes are huge, spanning from the Pannonian Basin to eastern Central Asia. The results of our project clearly reject the hypothesis that steppe organisms reached the Alps by recent range expansion from east to west during cold periods of the late Pleistocene. Rather, our results emphasise for the first time that, from a biodiversity point of view, extrazonal steppes are not the mere appendix of the zonal Eurasian steppes. In more detail, we showed that in five out of six investigated species, populations from extrazonal steppes are strongly divergent from those from zonal steppes. The divergence is partly so pronounced that descriptions of new, European endemic taxa are required. Our data also reject the hypothesis that the phylogeographic patterns of steppe plants and animals are congruent, which implies idiosyncratic responses of species to climatic oscillations instead of range shifts of entire communities. Finally, for some of the investigated species, the fine-scale resolution facilitated by genome-scanning data provided evidence for genetic exchange among insular steppe habitats of different valleys implying that high mountain ranges do not pose barriers to dispersal. The fact that in several species extra-zonal populations of steppe biota need to be treated as separate evolutionary entities, independent from their zonal distribution, strongly emphasises the conservational value and the uniqueness of the remaining dry grasslands in the Alps and adjacent areas. We are confident that our findings will act as a new basis for conservationists and policy makers to advocate a future, scientifically founded conservation of steppes in Europe.