Genomic Data Reveal Multiple Introduction Sources and Limited Post‐Colonization Gene Flow in Southeast Michigan Invasive Red Swamp Crayfish ( <i>Procambarus clarkii</i> )

Understanding the colonization history and factors associated with changes in distribution and abundance of invasive species is paramount to inform control measures that prevent further spread and facilitate eradication. We investigated spatial patterns in genetic diversity and differentiation of the globally invasive species, the Red Swamp Crayfish (<i>Procambarus clarkii</i>) at a recent invasion front in the Detroit metropolitan area of southeast (SE) Michigan, USA. Genomic data based on collections of 763 individuals from 20 waterbodies and 2675 single nucleotide polymorphism (SNP) loci were used to estimate genetic diversity and spatial genetic structure and to test the hypotheses of gene flow and secondary spread. We identified strong genetic structure, and demographic (coalescent) analysis supported models consistent with multiple introductions from separate genetic lineages. Across the study area, seven genetically distinct clusters were identified. We found evidence of limited dispersal consistent with an isolation-by-distance pattern of gene flow among waterbodies. We also detected evidence of secondary dispersal from early invasive populations consistent with a bridgehead effect. Local landscape features including hydrological features, major land use types, and roads were not predictive of spatial genetic relationships among waterbodies within geographic clusters. Results suggest that the <i>P. clarkii</i> invasion of SE Michigan has proceeded through a combination of repeated introductions and secondary spread at fine spatial scales. The highly developed landscape of the metropolitan Detroit area did not appear to deter the movements of <i>P. clarkii</i>, suggesting further spread is likely.