Landscape context and dispersal ability as determinants of population genetic structure in freshwater fishes

Dispersal is a critically important process that dictates population persistence, gene flow, and evolutionary potential, and is an essential element for identifying species conservation risks. This study aims to investigate the contributions of dispersal syndromes and hydrographic barriers on patterns of population connectivity and genetic structure in fishes occupying the particularly rugged and fragmented landscape of the Kimberley Plateau, Western Australia. We assessed population genetic structure between three neighbouring catchments (the Mitchell, King Edward, and Drysdale rivers) in three congeneric groups of freshwater fishes that exhibit varied dispersal syndromes within and among groups: (1) Melanotaenia australis and M. gracilis; (2) Syncomistes trigonicus and S. rastellus; and (3) Hephaestus jenkinsi and H. epirrhinos. Within each species we sampled the upper, middle, and lower reaches of each catchment and assessed patterns of gene flow between and within catchments using microsatellite markers. Our results suggest that contemporary connectivity between catchments is greatly limited or absent in all study species, regardless of their dispersal syndromes. However, gene flow within catchments varied in line with predicted dispersal potential, with poor dispersers exhibiting limited gene flow and significant genetic structuring. We conclude that the rugged landscape and historical habitat isolation has contributed to patterns of population fragmentation among fish populations from different river catchments. However, it appears dispersal syndromes influence connectivity and gene flow within catchments, where landscape constraints are not as pervasive. This study presents a comparative population genetic analysis of freshwater fishes with differing dispersal syndromes and colonisation ability. Our findings provide new insights into factors shaping patterns of biodiversity on the Kimberley Plateau, and the evolutionary uniqueness of fish communities from different river catchments draining the plateau. More broadly, they highlight the importance of accounting for dispersal-related traits when planning management and conservation strategies.