High degree of population subdivision in a widespread amphibian

Abstract

In general, amphibians are known to exhibit a higher degree of population subdivision than any other major animal taxa, but large-scale population genetic surveys of widely distributed species are still scarce, especially in the Eurasian continent. Using microsatellite markers and mitochondrial DNA sequences, we investigated the large-scale population genetic structure of the common frog (Rana temporaria)--one of the most widespread amphibians of the Palearctic region. Analyses of cytochrome b sequences revealed evidence for two distinct lineages inhabiting western and eastern parts of Europe. The separation of these lineages c. 700,000 years ago may have been induced by the onset of the Middle Pleistocene continental glaciations. Analyses of the variability of microsatellite loci within each of the clades revealed evidence for evolution of a high degree of population subdivision (FST approximately 0.23) even in northern Fennoscandia, colonized less than 10,000 years ago. The high level of substructuring is puzzling in the face of an apparently high dispersal capacity, as evidenced by the rather rapid recolonization of northern Europe. This suggests that processes other than restricted dispersal capacity need to be explored as explanations for the high degree of population subdivision in amphibians. The colonization of northern Europe has been accompanied by loss of genetic variability as evidenced by decreasing levels of intrapopulational genetic variability in microsatellite loci from south to north across Europe.

Sex-chromosome differentiation and ‘sex races’ in the common frog ( Rana temporaria )

“…A potential role of phylogeography was suggested to account for the latitudinal trend in sex-chromosome differentiation across Fennoscandia [28]: two divergent eastern and western mtDNA-lineages of R. temporaria meet south of Fennoscandia [39], raising the possibility that the trend documented reflects a divergence between lineage-specific systems of sex determination. However, the point must also be made that the distribution of Witschi's sex races fits climatic gradients [20], while that of mitochondrial lineages fits roads of postglacial recolonization (e.g.…”

The genetic contribution to sex determination and number of sex chromosomes vary among populations of common frogs (Rana temporaria)

“…Thus, a parsimonious interpretation is that LG 2 is the ancestral sex chromosome in R. temporaria, with the recent and seemingly localized addition of LG 7 . Postglacial colonization of northern-boreal regions by common frogs occurred very lately (o10 kya; Palo et al, 2004). Generation time under harsh climates can be estimated to 8 years (assuming age at first reproduction to be 4 years and annual survival rate 80%; Miaud et al, 1999), possibly more because fecundity increases with age.…”

Amphibian phylogeography: a model for understanding historical aspects of species distributions

“…Northerly (postglacial) colonization probably occurred from refugia harbouring this lineage in the Carparthian basin and in southern Russia. Cytb analysis of R. temporaria detected two main lineages, in eastern and western Europe, respectively, that diverged in the mid-Pleistocene about 700 000 YBP (Palo et al, 2004). Data from eight microsatellite loci demonstrated a high level of population differentiation across the range of R. temporaria, including previously glaciated regions that can only have been occupied within the last 10 000 years.…”