Evolutionary relationships of the sooglossid frogs of Seychelles

The granitic islands of the Seychelles are Gondwanan fragments, and have remained isolated for in the region of 63 million years. Their origin dates to a period contemporaneous with the Cretaceous-Paleogene boundary extinction event, and volcanic activity that formed the Deccan Traps. The archipelago is a biodiversity hotspot, and much of its biota is endemic. Among Seychelles fauna, the sooglossid frogs are globally significant. The only amphibian family entirely restricted to an archipelago, until recently they were found on just two islands in the Seychelles. Sooglossids are amongst the top 100 EDGE amphibians, and currently classified by the IUCN as either Endangered (Sooglossus sechellensis, Sechellophryne gardineri) or Critically Endangered (So. thomasseti, Se. pipilodryas). In 2009 a population of sooglossid frogs was discovered on a third island, Praslin, and subsequently revealed to be a unique lineage. Morphometric and bioacoustic data from the Mahé, Silhouette, and Praslin sechellensis frogs (the sechellensis group), and DNA sampling from each island population of the Sooglossidae, was collected for an assessment of the sechellensis group. Principal component and discriminant function analyses of morphometric data identified separate populations of sechellensis group frogs; Silhouette frogs were the largest with shorter hind limbs; Praslin frogs were the smallest but possessed longer hind limbs; Mahé frogs were also distinct but shared greater similarities with Silhouette frogs. Vocalisations of the Praslin Sooglossus differed from other sechellensis group frogs in structure, pulse rate, primary note length, and call duration. Mitochondrial phylogenies identified strongly supported, island-specific lineages of sechellensis group frogs in independent analyses, a pattern that was repeated for So. thomasseti. Haplotype networks for nuclear loci were less resolved than mtDNA phylogenies but showed geographic patterns. Combined mitochondrial and nuclear DNA species delimitation analyses showed strongly supported intraspecific discrimination within So. sechellensis, and So. thomasseti. An anuran phylogeny found a sister-group relationship between the Sooglossidae and Ranoidea, in accordance with previous work. Finally, divergence dating estimated the origin of the Sooglossidae in the Late Jurassic, the divergence of Sooglossus-Sechellophryne in the Late Cretaceous, followed by a sequence of key splits between genera (Sooglossus, Sechellophryne) and island-specific lineages (So. thomasseti, So. sechellensis) during the Late Paleogene, which correspond with a major decrease in global sea levels. However, both the anuran phylogeny and divergence dating analyses will benefit from additional loci and further, more stringent tests of the data and initial outputs. The analyses provide the basis for recognition of the Praslin Sooglossus and Silhouette sechellensis as novel taxa (confirmed candidate species), and pending further work, the Silhouette populations of So. thomasseti and Se. gardineri (unconfirmed candidate species). Urgent recognition of taxonomic status is required to facilitate targeted conservation to safeguard this distinct and unique anuran family. The demise of even one population would be a significant loss to global biodiversity and evolutionary history.