Diversity and distribution of reed frogs (Hyperolius spp.) on Bioko Island, Equatorial Guinea

Reed frogs (Hyperolius spp.) are the most species-rich genus in the family Hyperoliidae, a group of frogs endemic to sub-Saharan Africa and the Gulf of Guinea islands. Three species are endemic to oceanic islands in the archipelago, but the diversity and distribution of reed frogs on Bioko – a land-bridge island in the archipelago – remains unclear. Two species, H. tuberculatus and H. ocellatus ocellatus, were formally documented on Bioko in the colonial era, however, two additional reed frog species have been detected in recent surveys. In addition, observations of heterospecific amplexus suggest one of the unidentified species and H. o. ocellatus may be hybridising on the island. In this study, we examined mitochondrial DNA (mtDNA), nuclear DNA (nuDNA), morphological and acoustic data to confirm the tentative identifications of the reed frogs and determine if there is any evidence of hybridisation. Our data confirm that the two unidentified species are H. endjami and H. fusciventris, and that Bioko H. endjami have unique genetic diversity not shared with the mainland population. Additionally, our mitochondrial (16S) and nuclear DNA (CMYC) haplotype networks suggest that H. o. ocellatus and H. endjami are not hybridising on Bioko. Finally, we report colour pattern variation in H. endjami and H. o. ocellatus that is unique from populations on the continent, and describe male advertisement calls of Bioko H. endjami and H. o. ocellatus. Our study provides a first look at the diversity and distribution of reed frogs on Bioko Island and sets the stage for future studies of the ecology, evolution, and conservation of this island community. KEYWORDS: hybridisation, polymorphism, mitochondrial and nuclear DNA, morphology, land-bridge island