Relationships in Genetic Heterozygosity and Behavior in Four Southeastern Populations of Cotton Rats (Sigmodon Hispidus)

Abstract

Relationships between behavior and genic heterozygosity were investigated using young adult male and female cotton rats (Sigmodon hispidus) collected from naturally occurring populations at three main1and and one beach localities in the southeastern United States. General activity, exploratory behavior and agonistic behavior were measured. Genic heterozygosity was estimated by direct count for individuals and populations by examining allelic variation in 28 proteins detectable by starchgel electrophoresis. Mean behavioral performance of the Florida populations increased with increasing percent average genic heterozygosity in exploration and aggression tests, whereas South Carolina populations did not. Some behaviors showed a significant association with individual heterozygosity, expressed as the number of heterozygous loci per individual when rats were pooled for analysis. It is concluded that genic heterozygosity affects the performance of behavior important to wild cotton rat survival and reproduction. In addition, cotton rat populations from more southern latitudes demonstrated greater behavioral performance and genic heterozygosity than more northern populations. It is hypothesized that behavior, genetic heterozygostiy, and corresponding behavior-genetic relationships regulate population size in cotton rats. A model for the genetic regulation of small mammal populations is presented, based on the premise that individual survival, reproductive success, and movement patterns of cotton rats are related to genetic heterozygostiy.