Spatial and Temporal Genetic Variability of the Eastern Cottontail on West Texas Playa Basins

Abstract

Spatial and temporal changes in allelic frequency, genotypic proportions, and total and single locus heterozygosity of the eastern cottontail ( Sylvilagus floridanus ) were studied on two playa lake basins in the Texas Panhandle. Playa basins in this region are separated by extensive areas of agricultural and pasture lands, and therefore constitute the only significant cottontail habitat. Blood plasma samples were obtained from 543 individuals captured on both playa basins, during seven live-trapping periods from February through November, 1981. Adult and seven juvenile age classes were identified. Prereproductive adult cottontail populations had observed genotypic proportions that deviated significantly from expected Hardy-Weinberg equilibrium, seemingly the result of heterozygote deficiencies related to differential overwinter selection and/or nonrandom genotypic dispersal. These findings are inconsistent with previous studies in which increases in heterozygosity were shown to correlate with superior fitness. Significant ( P > 0.05) changes in allelic frequencies, genotypic proportions, and heterozygosity were related to population demographic characteristics. Apparent random matings by individuals of parental genotypes and subsequent juvenile recruitment dampened or eliminated the disequilibrium in Hardy-Weinberg proportions. Changes in population number due to reproductive recruitment and dispersal were accompanied by changes in gene frequency and heterozygosity. Spatial differences in genetic attributes were maintained between the two playa basins throughout the study because of the large distances between breeding groups. However, parallel trends were observed in population genetic and demographic characteristics on both playa basins.