Genetic structure of the Lesser Gymnure (Genus Hylomys) in SE-Asia: evidence for two species

The Lesser Gymnure is a small galericine Insectivore living in the mainland forests of Southeast Asia, including the major islands of Sumatra, Java and Borneo. It is the only representative of the supposed monospecific genus Hylomys which is morphologically rather constant over its geographic range. Only marginal subspecific differentiation is currently recognized based in slight pelage colour variations. We report here the results of 35 gene loci revealed by protein electrophoresis on 23 specimens sampled over most of Southeast Asia. They were compared with outgroup, Erinaceaus europeaus, member of a distinct subfamily. The surveyed populations of Lesser Gymnures clearly group themselves into distinct taxa, one of which seems restricted to Sumatra, while the other occupies the whole geographic range. The genetic distance between these groups is two times greater than the divergence observed within groups: it is of the same order of magnitude as what is usually reported for congeneric mammal species, which supports their specific distinction. The lack of gene flow is also demonstrated by several diagnostic loci defining unambiguously each species. Both are only distantly related to the outgroup, a result which is consistant with their actual classification into two distinct subfamilies (Erinaceae and Galericinae). Concordant genetic and geographic subdivision of the widespread species further suggest that eustatic sea level changes during the Pleistocene produced predictable patterns in species differentiation.

Is chytridiomycosis an emerging infectious disease in Asia?

The disease chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis (Bd), has caused dramatic amphibian population declines and extinctions in Australia, Central and North America, and Europe. Bd is associated with >200 species extinctions of amphibians, but not all species that become infected are susceptible to the disease. Specifically, Bd has rapidly emerged in some areas of the world, such as in Australia, USA, and throughout Central and South America, causing population and species collapse. The mechanism behind the rapid global emergence of the disease is poorly understood, in part due to an incomplete picture of the global distribution of Bd. At present, there is a considerable amount of geographic bias in survey effort for Bd, with Asia being the most neglected continent. To date, Bd surveys have been published for few Asian countries, and infected amphibians have been reported only from Indonesia, South Korea, China and Japan. Thus far, there have been no substantiated reports of enigmatic or suspected disease-caused population declines of the kind that has been attributed to Bd in other areas. In order to gain a more detailed picture of the distribution of Bd in Asia, we undertook a widespread, opportunistic survey of over 3,000 amphibians for Bd throughout Asia and adjoining Papua New Guinea. Survey sites spanned 15 countries, approximately 36° latitude, 111° longitude, and over 2000 m in elevation. Bd prevalence was very low throughout our survey area (2.35% overall) and infected animals were not clumped as would be expected in epizootic events. This suggests that Bd is either newly emerging in Asia, endemic at low prevalence, or that some other ecological factor is preventing Bd from fully invading Asian amphibians. The current observed pattern in Asia differs from that in many other parts of the world.

Origin and genome evolution of polyploid green toads in Central Asia: evidence from microsatellite markers.

Polyploidization, which is expected to trigger major genomic reorganizations, occurs much less commonly in animals than in plants, possibly because of constraints imposed by sex-determination systems. We investigated the origins and consequences of allopolyploidization in Palearctic green toads (Bufo viridis subgroup) from Central Asia, with three ploidy levels and different modes of genome transmission (sexual versus clonal), to (i) establish a topology for the reticulate phylogeny in a species-rich radiation involving several closely related lineages and (ii) explore processes of genomic reorganization that may follow polyploidization. Sibship analyses based on 30 cross-amplifying microsatellite markers substantiated the maternal origins and revealed the paternal origins and relationships of subgenomes in allopolyploids. Analyses of the synteny of linkage groups identified three markers affected by translocation events, which occurred only within the paternally inherited subgenomes of allopolyploid toads and exclusively affected the linkage group that determines sex in several diploid species of the green toad radiation. Recombination rates did not differ between diploid and polyploid toad species, and were overall much reduced in males, independent of linkage group and ploidy levels. Clonally transmitted subgenomes in allotriploid toads provided support for strong genetic drift, presumably resulting from recombination arrest. The Palearctic green toad radiation seems to offer unique opportunities to investigate the consequences of polyploidization and clonal transmission on the dynamics of genomes in vertebrates.