Hierarchical Organization of Genetic Variation in the Sailfin Molly, Poecilia Latipinna (Pisces: Poeciliidae)

Twenty-two percent of all allozyme variation documented in the sailfin molly (Poecilia latipinna) was attributable to regional differences, while only 3% was attributable to differences among demes within regions. Of the variation documented in a given region, 6-12% was attributable to variation among demes. Cluster analyses supported these conclusions quantitatively. Spatial-autocorrelation analyses offered more explicit support: demes separated by increasingly greater distances were increasingly dissimilar. Analyses using F statistics and rare alleles suggest "effective gene flow rates" (the product of effective population size and gene flow rate) of approximately 4, a level more than sufficient to prevent local independence of gene-frequency dynamics. These results, taken together, suggest that mollies do not have a population structure conducive to the operation of Wright's shifting-balance process and make the striking patterns of interdemic variation in body size and sexual behavior observed in this species all the more interesting.