| Summary: | Bigmouth Buffalo (Ictiobus cyprinellus) is an understudied large-bodied fish species that can live over 120 years, native to central North America. Bigmouth buffalo’s distribution ranges from Saskatchewan, Canada, to the Gulf of Mexico, and are particularly widely distributed within the Mississippi River basin in the US. Within Canada, they are divided into two populations: the Saskatchewan-Nelson River population in the Canadian prairies, and the Great Lakes-upper St. Lawrence River population in Ontario. The Saskatchewan-Nelson River population is listed as a species of special concern due to observed declines within the Qu’Appelle River, understanding if there is genetic mixing between Saskatchewan and Manitoba was one of the research priorities recommended in the 2019 species at risk management plan. Furthermore, bigmouth buffalo have become a popular sport fish in the US but lack harvest limits across most of the US. This study aimed to resolve the lack of population genetic structure of bigmouth buffalo across much of their range. I used restriction site-associated DNA sequencing to examine signatures of population divergence across five geographic areas, Minnesota and Missouri in the US, and Ontario, Manitoba, and Saskatchewan in Canada. Filtering of raw data followed the de novo stacks pipeline with a final data set of 12,071 single nucleotide polymorphisms (SNPs). I analysed the genetic data with observed and expected heterozygosity’s, inbreeding co-efficient, pairwise and population specific Fst, principal components analysis, admixture analysis, analysis of molecular variance, effective population size, SNPs under selection, and assignment accuracy to population of origin. I found evidence for population structure between the five locations with unidirectional admixture from Saskatchewan to Manitoba. Bigmouth buffalo had low genetic diversity suggesting an ancestral population bottleneck during the last glacial period or small recolonizing populations leading to founder effects in the populations ...
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