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

A range-wide survey of Dakotaskipper (Hesperia dacotae) populationsassessed levels of genetic variability andgeographic scale of population structure inthis species of conservation concern. Thisspecies exists on isolated patches of nativetall- and mixed-grass prairie within a highlymodified landscape dominated by agriculture. It has been extirpated from the southernportion of its range and has sufferedrange-wide declines. Nine populations weresampled from western Minnesota, eastern SouthDakota, and southern Manitoba. Starch gelelectrophoresis was used to resolve 21 isozymeloci in 278 Dakota skippers. Dakota skipperpopulations were approximately as variable asother lepidopterans found in isolated habitats. Genetic distances indicated that Manitobapopulations were somewhat distinct from ones inMinnesota and South Dakota. Isolation-by-distance was detected range-wideand among the seven southern-most populations. Genetically effective immigration rates weresmall at both range-wide and regional scalesand effective populations sizes were lowsuggesting that Dakota skipper populations aregenetically isolated from one another, althoughthey were likely more connected in the recentpast. Genotype assignment tests revealed twoclusters of populations in Minnesota and SouthDakota that were not apparent from theisolation-by-distance results. Significantheterozygote deficiencies relative toHardy-Weinberg expectations and high inbreedingcoefficients suggest structure within samplelocations. Management recommendations includethe maximization of effective population sizein each Dakota skipper population to offset theeffects of drift and habitat corridors in somecases. Habitat management should consider thewithin-site population structure and possibletemporal population structure detected in thisstudy.