Genetic divergence and the Pleistocene history of the alpine butterflies Boloria improba (Nymphalidae) and the endangered Boloria acrocnema (Nymphalidae) in western North America

Abstract

Allozymes were assayed at 20 presumptive loci in increasingly isolated populations of alpine butterflies in the Boloria improba species-group including the endangered Boloria acrocnema. Populations of this Holarctic group were sampled along the Rocky Mountain Cordillera from the Yukon Territory to Colorado. Samples from a more widely distributed and generalist butterfly, Boloria titania, were assayed at 18 presumptive loci for comparative purposes. Estimates of heterozygosity, percent polymorphic loci, mean number of alleles per locus, genetic identity, and distribution of regional and private alleles indicated that the current distribution of butterflies in the B. improba group is the result of a vicariance event. During the last Wisconsin glacial maximum (20 000 to 18 000 years BP) the range of ancestral B. improba was split into Alaskan refugial populations and southern glacial-margin populations. Subsequent dispersal into an ice-free corridor 12 000 to 10 000 years BP from the Alaskan refugial populations gave rise to British Columbia and Alberta B. improba populations. Results from B. titania support these findings.