Abstract

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Britten, H.B., and J.W. Glasford. 2001. Conservation genetics of the Dakota Skipper (Hesperia dacotae). Final report submitted to the Natural Heritage and Nongame Research Program, Minnesota Dept. of Natural Resources. 27 pp.

Abstract:

A range-wide genetic survey of Dakota skipper (Hesperia dacotae) populations was carried out to assess levels of genetic variability and geographic scale of population structure in this species of conservation concern. The Dakota skipper is on the Threatened Species list in the state of Minnesota and the Province of Manitoba, Canada, and is currently being considered for US federal protection. It exist on isolated patches of native tall-grass prairie within a highly modified landscape dominated by agriculture. It has been extirpated in the southern portion of its range in Iowa and has suffered range-wide declines.

Nine populations were sampled as follows: five from western Minnesota, two from eastern South Dakota, and two from central Manitoba. The sampling protocol was designed to minimize the demographic effects of removing individuals from these populations. Males were hand-netted and frozen in liquid nitrogen for later analysis. All netted females were released immediately. Proteins were extracted via standard methods and starch gel electrophoresis was carried out on 281 Dakota skippers. Twenty-one allozyme loci were resolved for this study.

Dakota skipper populations were found to be approximately as variable as other lepidopterans with highly fragmented habitats. Mean individual heterozygosity and percentage of loci polymorphic were generally lower in the Dakota skipper than in other lepidopterans (all butterflies) that exist in more continuous habitat. Genetic distances indicated that Manitoba populations were somewhat distinct from the southern ones in Minnesota and South Dakota. Isolation-by-distance was detected range-wide and among the seven southern-most populations in Minnesota and South Dakota. Genetically effective immigration rates were small at both range-wide and regional scales. Effective populations sizes were shown to be low in the sampled populations. These results suggest that Dakota skipper populations are genetically isolated from one another, although they were likely more connected in the recent past. The results also suggest that genetic drift is an important structuring force in these populations. Significant heterozygote deficiencies relative to Hardy-Weinberg expectations and high inbreeding coefficients suggest small-scale structure within sample locations.

Management recommendations include the maximization of effective population size in each Dakota skipper population to offset the effects of drift. Habitat corridors to enhance gene flow between nearby populations may be an option for the Hole-in-the-Mountain, Prairie Coteau, and Starbuck, MN, populations. Habitat management should consider the small-scale (within site) population structure and possible temporal population structure detected in this study by further investigating within-site movements and maintaining all potentially suitable habitat at Dakota skipper sites.

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