Population genetics and phylogeography of North American Merlins (Falco columbarius) in the post‐DDT era

In North America, the population genetic structure of many raptor species has been shaped by patterns of post‐glacial population expansion and anthropogenic forces, such as the widespread use of the organochlorine pesticide dichlorodiphenyltrichloroethane (DDT) during the mid‐20th century. While common themes of post‐glacial avian population expansion have emerged, little is known about the genetic impacts of DDT on raptor species that experienced a population bottleneck but were not the focus of conservation efforts. We investigated how the combination of post‐Pleistocene environmental change and the DDT‐era population bottleneck have influenced the contemporary population structure of Merlins Falco columbarius in North America. We genotyped migrating Merlins across North America (n = 272) at 23 polymorphic microsatellite loci and generated sequence data for a 569‐base‐pair segment of the mitochondrial control region. We used hierarchical analysis of molecular variance, pairwise FST/ϕST comparisons and Bayesian clustering analyses to assess genetic differentiation between individuals from eastern and western North America, distinct migratory flyways, and three recognized North American subspecies. Across all analyses, we found low or no population differentiation, suggesting that North American Merlins largely comprise one panmictic population showing evidence of a post‐glacial population expansion with little genetic differentiation detected between regions. Furthermore, we did not detect a contemporary signal of a genetic bottleneck that could have resulted from the DDT‐era population decline with the markers used in this study. Consistent with other avian species, we found a correlation between allele length variation at a microsatellite isolated from the 3′ untranslated region of the ADCYAP1 gene and migratory versus sedentary characteristics in Merlin subspecies. We detected two common mitochondrial control region haplotypes in the geographical regions sampled, a unique pattern among other widespread North American raptor species. This study furthers our understanding of the genetic and demographic history of Merlins in North America and can inform future genomic studies of this species.