Discrepancy in the degree of population differentiation between color-morph frequencies and neutral genetic loci in the damselfly Ischnura senegalensis in Okinawa Island, Japan.

Evaluation of relative contribution of natural selection and stochastic processes to population differentiation has been of great interest in evolutionary biology. In a damselfly, Ischnura senegalensis, females show color dimorphism (gynochrome vs. androchrome), and color-morph frequencies are known to greatly vary among local populations within Okinawa Island, a small island of Ryukyu Archipelago, Japan. In this study, to examine the effects of natural selection and stochastic processes on the within-island variation in color-morph frequencies, we compared the degree of population differentiation at the color-morph locus with that at a mitochondrial DNA region and ten nuclear microsatellite loci. F ST values at the neutral loci were close to zero, indicating presence of sufficient gene flow (dispersal of adult individuals) between the local populations. In contrast, F ST values at the color-morph locus were significantly different from zero. These results suggest that variation in female color-morph frequencies observed among local populations in Okinawa Island has been caused by divergent selection acting on the phenotype and/or genes tightly linked with the color locus.