Ancient Fishes in Modern Riverscapes: A Genetic Assessment of Gar (Lepisosteidae) in Illinois’ Watersheds

Ancient fish species are key components of communities in big river systems, and are increasingly relevant in delivering ecosystem services to communities in these systems. Their efficacy to contribute to ecosystem processes and services hinges upon their persistence. However, anthropogenic and natural restrictions, from the past and present, are undoubtedly affecting these communities. Considering these mechanisms and their effects over geological and evolutionary timescales can provide insights into the riverscape genetic structure of these freshwater species and ultimately inform adaptive management to yield sustainable, resilient populations. In this study, we sought to 1) assess the evolutionary legacy of gar in Illinois’, 2) assess the degree of gene flow and identify barriers to genetic connectivity, and 3) assess the level of introgression among three Illinois gar species. A total of 370 individuals across three species of gar (Lepisosteus oculatus, L. osseus, and L. platostomus) were considered for this study. Individuals were collected from thirty sites spread throughout six watersheds. Mitochondrial DNA sequence data were derived to address objective 1, while 7 microsatellite loci were leveraged to address objectives 2 and 3. Preliminary results suggest that a deep evolutionary history has played a role in shaping extant genetic diversity, while contemporary processes (including fish passage barriers) have presented emerging challenges to genetic connectivity. Finally, these results suggest that a changing global climate may exacerbate these impacts into the future. By understanding riverscape genetics of these ancient fishes, we gain insights to the impacts of environmental change, can extrapolate the impacts of future ecological uncertainty, and develop strategies aimed at mitigating deleterious impacts of an ever-changing world.