Biochemical Genetics of Mosquitofish. I. Environmental Correlates, and Temporal and Spatial Heterogeneity of Allele Frequencies within a River Drainage

populations varied as a function of the distance from the first dam from the mouth of the river. Two of six populations which had been sampled in a previous study several years before this one showed significant changes in allele frequencies. Differences in allele frequencies were related to major environmental categories, such as water temperature, flow characteristics and elevation of the site. These observations are not consistent with the neutrality model but suggest a genetically dynamic species subjected to both selection and stochastic processes as described in the shifting balance model of evolution.