Understanding the origin of the most isolated endemic reef fish fauna of the Indo-Pacific: Coral reef fishes of Rapa Nui

Aim To understand the origin of the most isolated endemic fish fauna of the Indo-Pacific, Easter Island (Rapa Nui), and to infer divergence times and colonization routes of the endemic coral reef fish fauna from their closest relatives. Location Easter Island, Pacific Ocean. Methods Samples of ten species were used: six small-range species endemic to Rapa Nui and Motu Motiro Hiva (Salas y Gomez) (i.e. small-range endemic species) and four large-range species endemic to the southern subtropical Pacific (i.e. large-range endemic species). We present phylogenetic reconstruction results based on mitochondrial (1 to 5) and nuclear (1 to 6) loci to place these endemic species in their respective family phylogenies (8). Using these newly calibrated phylogenetic trees, information of species distributions and geological data, we inferred the divergence times from the closest relatives of these ten endemic fishes, compared biogeographical history estimation models to reconstruct their ancestral geographic ranges, colonization routes and underlying mechanisms of speciation. Results The divergence times (i.e. divergence times from the closest relatives) of all of the small-range endemics studied were more recent than the age of Rapa Nui and Motu Motiro Hiva; thus, these species can be considered as neoendemics. Biogeographical history estimation models indicated that speciation following a founder-event is the most likely scenario. In contrast, the divergence estimates of the large-range endemic species were highly variable. This being said, the divergence times of all species were more recent than the age of the oldest islands within their distributions. Main conclusions Taken together, these results demonstrate that Rapa Nui acts as a cradle of coral reef biodiversity, being responsible for the emergence of small-range endemic fish species, but also a route of dispersion for several large-range endemics and as a stepping stone in the diversification of the Myripristis and Pseudolabrus genera. While no common divergence time was recovered for all of the ten endemic species studied here, the common mechanism of speciation following a founder event was recovered for most of the small-range endemic species.