Small, specialised and highly mobile? The tree-hole breeding frog, Phrynobatrachus guineensis, lacks fine-scale population structure

Abstract

Data on population dynamics and distribution are of primary interest to biologists because they reveal information about the species' ecology and evolution and are thus essential for conservation efforts. Patchily distributed species are especially interesting for conservation studies, because of their sometimes very specific environmental requirements. An example of a highly specialised species is the leaf litter frog Phrynobatrachus guineensis. This small species (20 mm) is short lived, presumably weakly mobile and highly specialised because it uses tree-holes and other small water-filled cavities with very particular abiotic and biotic characteristics for breeding. Previous field studies revealed that P. guineensis exhibited a clumped distribution in Tai National Park (TNP), Ivory Coast, suggesting that the park's population might be subdivided into several (sub)populations. We therefore investigated the population genetic structure of the park using four microsatellite loci, which are the first described microsatellite markers for any African anuran in general and for a species of the family Phrynobatrachidae in particular. In contrast to our expectations, we detected only a slightly significant genetic differentiation based on allele frequencies. We found no correlation between the geographic and genetic distances (isolation by distance) and Bayesian clustering revealed no genetic substructure. We did, however, detect small but significant genetic differentiation between subsequent seasons. The most probable explanation for the lack of population structure is that P. guineensis is more mobile than expected. Adults, most likely females but possibly also juveniles, are able to traverse matrix habitats in which no breeding activities were detected. The temporal genetic differentiation may be the consequence of genetic drift due to high mortality rates and/or non-random mating. Both explanations would be consistent with our field data.