From endemism to widespread distribution: phylogeography of three amphidromous Sicyopterus species (Teleostei: Gobioidei: Sicydiinae)

Island freshwater habitats are colonised by amphidromous fish, which display an oceanic larval phase while the rest of their life cycle takes place in rivers. In the present study we evaluated the population structure of the widespread Sicyopterus lagocephalus (Gobioidei) over its Indo-Pacific distribution range, which encompasses the island chain (Indonesia - Papua New Guinea - Malaysia) known as the Indo-Pacific Barrier (IPB). Additional analysis of 2 endemic species, S. aiensis (Vanuatu) and S. sarasini (New Caledonia), living in sympatry with S. lagocephalus, represented comparative material and was used as the basis for an assessment of endemism and dispersal. Mitochondrial cytochrome b sequence data were obtained for 332 S. lagocephalus, 210 S. aiensis and 87 S. sarasini across each species' range. Haplotype networks and F-statistics were used to determine patterns of population structure. A discrete phylogeographic diffusion model under a time-scaled coalescent tree prior was used to assess the history of the spatial expansion of S. lagocephalus across its wide spatial distribution. S. lagocephalus demonstrates high population structure across the IPB. It also displays a strong structure between Tahiti and all other locations sampled. No other population structure was identified in the entire western Pacific. Phylogenetic reconstruction and coalescence analysis indicate that the oldest population originated in the western Pacific, from which the eastern Pacific and the Indian Oceans were colonised. For the 2 endemic species, no genetic structure was identified across their respective ranges. From the genetic results associated with known elements of the life history of these species, we improved our understanding of the simultaneous existence of geographically close endemic species and a widespread species.