Lack of genetic differentiation among widely spaced subpopulations of a butterfly with home range behaviour

We examine seven geographically separate subpopulations of Heliconius chari thonia, a butterfly with well-documented home range behaviour, in Miami-Dad e County, Florida, for genetic differentiation using cellulose acetate elec trophoresis. These subpopulations exhibit little genetic variation (percent polymorphic loci = 27, average heterozygosity = 0.103) especially in compa rison to populations of the same and related species from mainland South Am erica. Allele frequencies do not differ among the subpopulations in south F lorida and estimates of Wright's fixation index (F-ST) support that there i s no detectable genetic differentiation among them. This result supports an earlier finding that the dispersal ability of Heliconius butterflies may b e underestimated. However, it is unlikely that increased dispersal ability alone could account for the lack of genetic differentiation observed among subpopulations separated by almost 80 km. Given the likely effective popula tion size of these subpopulations (N-e = 205) and the average generation li me of this species in the subtropics (in the range of 30-90 days), this lac k of genetic differentiation is best explained by current or very recent ge ne flow following a stepping-stone model. Furthermore, this result provides evidence that the current extensive degree of habitat fragmentation surrou nding the city of Miami does not limit gene flow among urban subpopulations of Heliconius charithonia.