Genetic structure and diversity of spotted gar (Lepisosteus oculatus) at its northern range edge: implications for conservation

Understanding the spatial context of genetic variation for species at risk is important for effective management and long-term survival of the species. We use multilocus microsatellite data to investigate the population genetic structure of the spotted gar (Lepisosteus oculatus) across its northern range edge in Canada. We then compare these northern individuals with samples taken from the southern core of the species range. For the northern samples, significant genetic differentiation among groups of individuals forming two major genetically distinct populations, and as many as 7-9 smaller subpopulations, was recovered using hierarchical Bayesian assignment methods and non-equilibrial discriminant function analyses. Spatial genetic variation is present, particularly at higher hierarchical groupings; however, some population admixture at sites is evident and is indicative of dispersal and gene flow among some locations or shared ancestry. Gene flow estimates among populations and subpopulations is very low, ranging from essentially complete isolation to as high as 5 %-suggesting that mechanisms in addition to geographic isolation are operating to create genetic structure. In Lake Erie, the physical isolation of Point Pelee appears to confer distinct genetic differentiation for those populations and provide a source of genetic variation for Lake Erie proper when breaches to the barrier beach occur. Results indicate that the northern edge populations are distinct from southern populations and should be conserved to maintain the overall genetic diversity of this species. Additionally, the asymmetrical genetic connectivity among the Point Pelee and Rondeau Bay sites highlights the sensitivity of Point Pelee to environmental perturbation and habitat degradation.