A TEST FOR ISOLATION-BY-DISTANCE IN CENTRAL ROCKY-MOUNTAIN AND GREAT-BASIN POPULATIONS OF EDITH CHECKERSPOT BUTTERFLY (EUPHYDRYAS-EDITHA)

A total of 18 Edith's checkerspot butterfly (Euphydryas editha) popula tions, seven from the central Rocky Mountains and II from the Great Ba sin, were assayed for genetic variability at 14-28 isozyme loci. Of th e surveyed loci, 13 were polymorphic in at least one of the sampled po pulations. Slatkin's method for detecting isolation-by-distance using a regression of pairwise estimates of interpopulation dispersal [log(N m)] against pairwise linear distance between populations [log(D)] was applied to these data. Central Rocky Mountain populations exhibited is olation-by-distance while the Great Basin populations did not. These d ifferences in population structure are probably due to the weak disper sal abilities of this species and to the insular nature of its habitat in the Great Basin.