Insights into population ecology and sexual selection in snakes through the application of DNA-based genetic markers

Hypervariable genetic markers have revolutionized studies of kinship, behav ioral ecology, and population biology in vertebrate groups such as birds, b ut their use in snakes remains limited. To illustrate the value of such mar kers in snakes, we review studies that have used microsatellite DNA loci to analyze local population differentiation and parentage in snakes. Four eco logically distinct species of snakes all show evidence for differentiation at small spatial scales (2-15 km), but with substantial differences among s pecies. This result highlights how genetic analysis can reveal hidden aspec ts of the natural history of difficult-to-observe taxa, and it raises impor tant questions about the ecological factors that may contribute to restrict ed gene flow. A 3-year study of genetic parentage in marked populations of the northern water snake showed that (1) participation in mating aggregatio ns was a poor predictor of genetic-based measures of reproductive success; (2) multiple paternity was high, yet there was no detectable fitness advant age to multiple mating by females; and (3) the opportunity for selection wa s far higher in males than in females due to a larger variance in male repr oductive success, and yet this resulted in no detectable selection on morph ological variation in males. Thus genetic markers have provided accurate me asures of individual reproductive success in this species, an important ste p toward resolving the adaptive significance of key features including mult iple paternity and reversed sexual size dimorphism, Overall these studies i llustrate how genetic analyses of snakes provide previously unobtainable in formation of long-standing interest to behavioral ecologists.