Abstract
I assessed the genetic differentiation of populations of Weidemeyer's admiral butterfly (Limenitis weidemeyerii) in central and eastern Colorado by using starch-gel electrophoresis. Wright's F-statistics indicated that there was significant differentiation, both within and between years, among the same populations analyzed for 2 successive years, and among populations, even those in close geographic proximity. Consequently, no correlation was found between the genetic identities and geographic distances between pairs of populations. To explain the genetic structure of populations, I estimated patterns of movement and effective sizes of populations. I assessed movement of individuals by using mark–recapture techniques, which indicated that travel over the season for both sexes was negligible (range 0–2850 m, mean 166 m). I estimated effective population sizes by using Pollak's methods, and as would be expected for populations with territorial social systems, effective sizes were small (ranging from 17 to 131, mean 61). These two factors, small and isolated populations, suggest that a significant portion of the genetic differentiation observed at allozyme loci among populations of Weidemeyer's admiral butterfly in Colorado is mediated by random genetic drift.