Phylogeographical structure and genetic diversity of Adonis vernalis L. (Ranunculaceae) across and beyond the Pannonian region

Abstract

Hypotheses of peripherality have characterised peripheral populations by increasing population differentiation and by declining genetic diversity towards the absolute range edge. However, such biogeographical patterns are not generally confirmed. Moreover, it was recently argued that lower levels of genetic diversity at the western and eastern periphery of the Eurasian steppe belt are only detectable by full-range longitudinal sampling. To uncover common genetic patterns of Central European steppe plants we here investigated Adonis vernalis populations across a transect towards their (north)westernmost range edge. Our study species shows a disjunct peripheral distribution with common Pannonian (Central Hungary) and more eastern occurrences (Romanian Dobruja) compared to the western edge of their continuous Pannonian range (Eastern Austria) and (north)westernmost isolated exclaves (Western Germany).We analysed 3–5 populations from each of these four study regions by cpDNA sequence (atpI-atpH, rpL16 intron) and AFLP fragment variation. Our AFLP results, based on 323 individuals, showed strong population differentiation, most pronounced within the Hungarian Pannonicum. Moreover, AFLP variation indicated high genetic diversity in the German exclave and at the Pannonian range edge in Eastern Austria compared to less peripheral, more eastern populations. While AFLP results are opposed to theoretical expectations, cpDNA data (i.e. 12 haplotypes) demonstrated lower haplotype diversity towards the (north)westernmost exclave and no monomorphic population within the Romanian Dobruja. Therefore, the latter marker complies with the peri-pheral transect predictions, although no material from Asia was included. Hence, not only the geographical scale is of importance when analysing phylogeographical patterns, but also possible differences of genetic marker systems. Showing strong signals of recent bottlenecks based on cpDNA in the German exclave, the biogeographical history of A. vernalis somehow differs from other steppe plants investigated to date across the same peripheral transect.