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 (Procambarus clarkii) 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 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 P. clarkii invasion of SE Michigan has proceeded through a combination of repeated introductions and secondary spread at fine spatial scales. The highly anthropogenically developed landscape of the metropolitan Detroit area did not appear to deter movements of P. clarkii, suggesting further spread is likely.

With continued global change, recovery of species listed under the Endangered Species Act is increasingly challenging. One rare success was the recovery and delisting of the Channel Island fox (Urocyon littoralis) after 90-99% population declines in the 1990s. While their demographic recovery was dramatic, less is known about their genetic recovery. To address genetic changes we conducted the first multi-individual and population-level direct genetic comparison of samples collected before and after the recent bottlenecks. Using whole exome sequencing, we found that already genetically depauperate populations were further degraded by the 1990s declines and remain low, particularly on San Miguel Island which underwent one of the most severe bottlenecks. The three other islands that experienced recent bottlenecks (Santa Rosa, Santa Cruz, and Santa Catalina islands) showed mixed results based on multiple metrics of genetic diversity. Previous island fox genomics studies showed low genetic diversity before the declines and no change after the demographic recovery, thus this is the first study to show a decrease in genetic diversity over time in U. littoralis. Additionally, we found that divergence between populations consistently increased over time, complicating prospects for using inter-island translocation as a conservation tool. The Santa Catalina subspecies is now federally listed as threatened, yet other de-listed subspecies are still recovering genetic variation which may limit their ability to adapt to changing environmental conditions. This study further demonstrates that species conservation is more complex than population size and that some island fox populations are not yet “out of the woods”.

Anthropogenic changes have altered the historical distributions of many North American taxa. As environments shift, ecological and evolutionary processes can combine in complex ways to either stimulate or inhibit range expansion. Here we examine the role of evolution in a rapid range expansion whose ecological context has been well-documented, Anna’s Hummingbird (Calypte anna). Previous work suggests that the C. anna range expansion is the result of an ecological release facilitated by human-mediated environmental changes, where access to new food sources have allowed further filling of the abiotic niche. We examine the role of gene flow and adaptation during range expansion from their native California north into Canada and east into New Mexico and Texas, USA. Using low coverage whole genome sequencing we found high genetic diversity, low divergence, and little evidence of selection on the northern and eastern expansion fronts. Additionally, there are few (if any) limits to gene flow across the native and expanded range. The lack of selective signals between core and expanded ranges could reflect i) an absence of novel selection pressure in the extended range (supporting the ecological release hypothesis), ii) swamping of adaptive variation due to high gene flow, or iii) limitations of genome scans for detecting small shifts in allele frequencies across many loci. Nevertheless, our results provide an example where strong selection is not apparent during a rapid, contemporary range shift.