Evidence of conservative range in mountain grasses during past climate change: Only contractions or local expansions possible

The ongoing biodiversity crisis associated with anthropogenic global warming has especially severe effects on mountain and cold-adapted species. The lesson from the postglacial period can provide examples for future predictions, but scenarios of the range shift of mountain species are not fully explored. Different stories could happen if a species achieved long-distance dispersal and reached lowland locations or if survived only in mountains, during the ice age. In the case of grasses, a key role in range dynamics is played also by polyploidy. Due to their enhanced genetic and physiological plasticity, polyploids are thought to be less likely to become extinct during global changes. The present study explores the postglacial range shifts in two Festuca species, which differ in range size (endemic vs widespread) and in ploidy level (diploid vs mixed-ploidy). We used phylogeography and distribution models to analyze changes in potential range during global warming. We achieved a sophisticated prediction by using modeling based on climate and edaphic factors. Our findings indicate a low level of gene flow between populations, irrespective of variation in distance, range size and ploidy. Slightly shorter genetic distances were observed between the tetraploid populations compared to the diploids. Our data indicates that diploids adapted to cold conditions were restricted to mountains during glaciations, while polyploids spread more widely during cold periods. Nevertheless, since the LGM it appears that all studied ranges have been rather conservative, with maybe some local contractions and expansions, especially in tetraploids. Moreover, tetraploids demonstrated the most stable potential range during climate warming. The studied cases are characterized by individual and complex range dynamics dependent on local conditions and cytotype behaviour. However, generally speaking, studied mountain species demonstrate a conservative range, which places them at risk of extinction during global warming due to the lack of effective means of escape.