Waiting for the snow to melt…
The Boloria improba species group consists of a series of populations of a common biennial arctic butterfly, the northern dingy fritillary (B.improba), which extends from arctic Canada and Alaska down the Rocky Mountain Cordillera with populations in British Columbia, Alberta, and Wyoming.The closely related Uncompahgre fritillary (Boloria acrocnema), known from only two colonies high in the San Juan Mountains of Colorado, occupies the southern end of this distribution.Capture-mark-release (CMR) estimates in 1987 revealed a steep decline in B. acrocnema numbers from earlier estimates at one site and the absence of the butterfly at the other.CMR and transect count estimates in 1988 indicate that both even-year broods consisted of approximately 250 individuals, a decline of about one order of magnitude from estimates made earlier in the decade.Eight B. improba group populations were sampled from the Yukon Territory to Colorado and 20 presumptive allozyme loci were assayed from them.Boloria titania were sampled from five B. improba group sites and 18 presumptive loci were assayed from each for comparison.The allozyme data suggest within colony structuring and low levels of gene flow between colonies.Significant negative correlations were found between estimates of allozyme variation and latitude, an indicator of geographical isolation in the B. improba group, that were not found in B. titania.Genetic identity estimates and the geographical distribution of individual alleles suggest that ancestral B. improba existed in Alaskan refugia and south of the major glaciers during the last glacial maximum and that central Canadian B. improba were derived from northern dispersers when the glaciers receded.Results from B. titania concur with this hypothesis.
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