The origins of marine fishes endemic to subtropical islands of the Southwest Pacific

Aim: Lineages colonizing subtropical oceanic islands often have to overcome geographical isolation and novel climate stressors to found new populations. Historical and ecological factors influence the success of colonization and subsequent diversification, leaving a signal in the genetic constitution of the diverged, range-restricted taxa. Here, we examined the historical biogeography of endemic marine fishes to quantify the role of geographical proximity and climate differences in determining colonization, and the underlying mechanisms of speciation.Location: Subtropical islands of the Southwest Pacific.Taxa: Thirty endemic marine ray-finned fishes from 17 genera.Methods: Using parametric biogeographical history models, we estimated the ancestral geographical ranges for 144 species based on time-calibrated phylogenies that included endemic species and their closest sister taxa, linking terminal nodes with geographical distribution classified into 14 biogeographical areas.Results: Ancestral range estimations revealed most species originated in Australia (66%), while only 10% and 7% originated in northern tropical Pacific locations and the East Pacific respectively, with 17% of species-range estimations being inconclusive. Vicariant events alone were identified as the most likely process shaping range evolution in 57% of the 14 best-fitting models, dispersal alone was favoured for 14% of species and both processes had a role for the remaining 29% of species. Across all phylogenies, likelihood-ratio tests confirmed that geographical distance and climatic differences constrained dispersal in 73% and 33% of species, respectively.Main Conclusions: Marine fishes endemic to subtropical islands of the Southwest Pacific originated by vicariant and jump-dispersal events mainly from ancestral populations in mainland Australia. Geographical distance and climatic differences are significant taxon-specific factors influencing the dispersal of marine fishes in the region.

Automated summary

This study examined the historical biogeography of endemic marine fishes in subtropical islands of the Southwest Pacific. The results showed that most species originated in mainland Australia and that both geographical proximity and climatic differences played a significant role in determining colonization and speciation.