GENETIC-VARIATION AND GENE FLOW WITHIN AND BETWEEN LOCAL-POPULATIONS OF THE TIMBER RATTLESNAKE, CROTALUS-HORRIDUS

Primers designed to amplify four microsatellite loci were used to scre en 32 timber rattlesnakes (Crotalus horridus) representing five geogra phically distinct hibernacula within a 6000-ha area. Average heterozyg osity at these loci approached 50% for the total sample of 32 individu als; therefore, these markers detected considerable genetic variation. Individuals using the same hibernaculum were more closely related to each other than they were to randomly selected individuals from the st udy site. In general, as geographic distance between hibernacula incre ased, genetic distance increased, and gene flow decreased; however, in some cases genetic distance did not correlate with geographic distanc e. Analysis of the movements of radiotracked snakes confirmed that pat terns of gene flow depended upon specific structural habitat features and were not simply related to the geographic distance between hiberna cula. The location of suitable basking habitat appeared to influence t he direction of movements and the distribution of alleles. These resul ts suggest that isolated hibernacula or a small number of hibernacula are the demographic units of C. horridus within this study site. We fo und evidence for the possible existence of nonamplifying (''null'') al leles for one of these loci (7-144), suggesting the importance of scre ening for null alleles before carrying out microsatellite analysis of a population.