Uncovering ecological diversification processes in islands: the case study of endemic reptiles in Socotra

Abstract

Islands are biodiversity hotspots, and prominent models for observing and interpreting ecological and evolutionary patterns. Ecological diversification on islands typically results in divergence of ecological niches. The Socotra Archipelago (Yemen) is a fragment of the Gondwana Supercontinent that was isolated from the Indian Ocean around 20 Myr ago when the Arabian and African plates separated. The reptile community living on this Archipelago is composed by 31 species, 29 of them endemic. In this study, trophic niche diversification (diet from faecal samples and stable isotopes from tail tips) of six gecko species of genera Haemodracon (two species) and Hemidactylus (four species) was examined. Each group conforms a monophyletic lineage with further intra*island speciation. Faecal samples and stable isotopes gave similar interspecific divergence between the six species examined. Models detected trophic*niche differences between sister species and also similarities between species of distant lineages. Microhabitat selection was a major factor that explained stable-isotope variation. Our results suggest that interspecific diet variation could be promoted by the occupation of different available microhabitats during ecological diversification. In a phylogenetic context, our study highlights some mechanisms that are driving reptile diversification and speciation in Socotra.