Small effective population size and fragmentation in Alpine populations of Bombina variegata: the combined effects of recent bottlenecks and postglacial recolonization

Amphibians are experiencing population declines in all continents due to anthropogenic factors. Evidence of demographic reduction and local extinction have been reported also for the yellow-bellied toad, Bombina variegata, along all its distributional range, which includes the Italian Alps. Here we genotyped at the mtDNA cytb and at 11 nuclear microsatellites 200 individuals of B. variegata from 9 populations sampled in Trentino (north-eastern Italy). We investigated the fine-scale population structure and we tested for genetic traces of population decline using different methods. We found that all populations showed low level of genetic diversity in comparison with other studies, low estimates of effective population size, and clear evidence of demographic decline. When the age of the decline is estimated, contrasting results are found. Some methods suggest a recent reduction of population size possibly associated with anthropogenic environmental changes, and others support a more ancient bottleneck dating back to the postglacial recolonization of the Alps. We suggest that both demographic processes occurred in the evolutionary history of the yellow-bellied toad populations, and we are now testing this hypothesis by simulation.