Mitochondrial DNA differentiation in the Japanese brown frog Rana japonica as revealed by restriction endonuclease analysis

Diversity, distribution and molecular species delimitation in frogs and toads from the Eastern Palaearctic

Biodiversity analyses can greatly benefit from coherent species delimitation schemes and up-to-date distribution data. In this article, we have made the daring attempt to delimit and map described and undescribed lineages of anuran amphibians in the Eastern Palaearctic (EP) region in its broad sense. Through a literature review, we have evaluated the species status considering reproductive isolation and genetic divergence, combined with an extensive occurrence dataset (nearly 85k localities). Altogether 274 native species from 46 genera and ten families were retrieved, plus eight additional species introduced from other realms. Independent hotspots of species richness were concentrated in southern Tibet (Medog County), the circum-Sichuan Basin region, Taiwan, the Korean Peninsula and the main Japanese islands. Phylogeographic breaks responsible for recent in situ speciation events were shared around the Sichuan Mountains, across Honshu and between the Ryukyu Island groups, but not across shallow water bodies like the Yellow Sea and the Taiwan Strait. Anuran compositions suggested to restrict the zoogeographical limits of the EP to East Asia. In a rapidly evolving field, our study provides a checkpoint to appreciate patterns of species diversity in the EP under a single, spatially explicit, species delimitation framework that integrates phylogeographic data in taxonomic research.

Sex chromosome evolution in frogs-helpful insights from chromosome painting in the genus Engystomops

The differentiation of sex chromosomes is thought to be interrupted by relatively frequent sex chromosome turnover and/or occasional recombination between sex chromosomes (fountain-of-youth model) in some vertebrate groups as fishes, amphibians, and lizards. As a result, we observe the prevalence of homomorphic sex chromosomes in these groups. Here, we provide evidence for the loss of sex chromosome heteromorphism in the Amazonian frogs of the genus Engystomops, which harbors an intriguing history of sex chromosome evolution. In this species complex composed of two named species, two confirmed unnamed species, and up to three unconfirmed species, highly divergent karyotypes are present, and heteromorphic X and Y chromosomes were previously found in two species. We describe the karyotype of a lineage estimated to be the sister of all remaining Amazonian Engystomops (named Engystomops sp.) and perform chromosome painting techniques using one probe for the Y chromosome and one probe for the non-centromeric heterochromatic bands of the X chromosome of E. freibergi to compare three Engystomops karyotypes. The Y probe detected the Y chromosomes of E. freibergi and E. petersi and one homolog of chromosome pair 11 of Engystomops sp., suggesting their common evolutionary origin. The X probe showed no interspecific hybridization, revealing that X chromosome heterochromatin is strongly divergent among the studied species. In the light of the phylogenetic relationships, our data suggest that sex chromosome heteromorphism may have occurred early in the evolution of the Amazonian Engystomops and have been lost in two unnamed but confirmed candidate species.