Evidence for evolutionary distinctiveness of a newly discovered population of sooglossid frogs on Praslin island, Seychelles

Amidst a worldwide decline in amphibian populations, those species endemic to islands remain an important focus for conservation efforts. The Sooglossidae are a family of frog species endemic to the Seychelles islands that are believed to have evolved in isolation for approximately 75 million years. Formerly thought to inhabit just two Seychelles islands (Mahé and Silhouette), a third population was discovered on Praslin in 2009. Phylogenetic analysis based on 438 bp of mitochondrial 16S rRNA suggests that the Praslin population is most closely related to Sooglossus sechellensis from Silhouette, and identifies these as two separate clades which together sit distinct from the population on Mahé. An average of 4.06% uncorrected pairwise sequence divergence between the Praslin and Silhouette populations suggests substantial evolutionary divergence rather than recent introduction. Discriminant function analysis also revealed differences in morphology in frogs from Praslin and Mahé. DNA sequences of two Praslin specimens group more closely with the Mahé population, indicating some shared haplotypes that suggest recent secondary contact. Tests for a genetic signature of recent population expansion on either island were not significant. Our results suggest substantial evolutionary divergence between the three populations of S. sechellensis, most likely following isolation due to changes in sea level in the Indian Ocean. Whilst further genetic sampling and ecological studies are needed, our initial phylogenetic analyses suggest that the sooglossid population on Praslin should be managed as an evolutionarily significant unit to retain the uniqueness of its genetic diversity and its evolutionary trajectory within this ancient family of amphibians.