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Abstract:
Whether freshwater fish colonize remote islands following tectonic or transoceanic dispersal remains an evolutionary puzzle. Integrating dating of known tectonic events with phylogenomics and current species distribution, we find that killifish species distribution eludes species dispersal by tectonic drift only. Investigating the colonization of a non-annual killifish (Pachypanchax playfairii) on the Seychelle islands, we found genetic support for trans-oceanic dispersal and experimentally discovered an adaptation to complete tolerance to seawater. At the macroevolutionary scale, despite their long-lasting isolation, non-annual golden panchax show stronger genome-wide purifying selection than annual killifishes from continental Africa. However, progressive decline in effective population size in a more recent time-scale likely led to the segregation of slightly deleterious mutations across golden panchax populations, which represents a potential threat for species preservation on the long run.
