Effects of a heterogeneous and highly urbanized landscape on gene flow in a coastal amphibian metapopulation

Dispersal is a crucial process in metapopulation persistence, both in terms of colonization-extinction dynamics and as a means to counter genetic drift and inbreeding in local demes. To investigate effective dispersal in a coastal dune metapopulation of Natterjack Toad (Epidalea calamita Laurenti), 256 larvae in four potential subpopulations were genotyped with 11 microsatellites. The grey dunes they inhabit are rare natural features on the Belgian coast. They are separated by urban areas and surrounded by agricultural fields. Because spatial landscape heterogeneity is expected to influence dispersal and genetic structure, we analyzed which landscape features affect functional connectivity and to what degree. Sixty landscape resistance scenarios were assessed using two different approaches. Our results revealed a genetic structure which was clearly not influenced by distance alone and source-sink dynamics among subpopulations. Urbanized areas seemed to hinder dispersal as well as surfaces with higher vegetation. On the other hand, distant subpopulations appeared functionally connected by the beach. Estimates of genetic diversity and effective population size further supported the landscape genetic results.