Genetic population structure of the Dakota skipper (Lepidoptera: Hesperia dacotae):: A North American native prairie obligate

A range-wide survey of Dakota skipper (Hesperia dacotae) populations assessed levels of genetic variability and geographic scale of population structure in this species of conservation concern. This species exists on isolated patches of native tall- and mixed-grass prairie within a highly modified landscape dominated by agriculture. It has been extirpated from the southern portion of its range and has suffered range-wide declines. Nine populations were sampled from western Minnesota, eastern South Dakota, and southern Manitoba. Starch gel electrophoresis was used to resolve 21 isozyme loci in 278 Dakota skippers. Dakota skipper populations were approximately as variable as other lepidopterans found in isolated habitats. Genetic distances indicated that Manitoba populations were somewhat distinct from ones in Minnesota and South Dakota. Isolation-by-distance was detected range-wide and among the seven southern-most populations. Genetically effective immigration rates were small at both range-wide and regional scales and effective populations sizes were low suggesting that Dakota skipper populations are genetically isolated from one another, although they were likely more connected in the recent past. Genotype assignment tests revealed two clusters of populations in Minnesota and South Dakota that were not apparent from the isolation-by-distance results. Significant heterozygote deficiencies relative to Hardy-Weinberg expectations and high inbreeding coefficients suggest structure within sample locations. Management recommendations include the maximization of effective population size in each Dakota skipper population to offset the effects of drift and habitat corridors in some cases. Habitat management should consider the within-site population structure and possible temporal population structure detected in this study.