DO BLACK-TAILED PRAIRIE DOGS MINIMIZE INBREEDING

Considerable controversy surrounds the importance of inbreeding in nat ural populations. The rate of natural inbreeding and the influences of behavioral mechanisms that serve to promote or minimize inbreeding (e .g., philopatry vs. dispersal) are poorly understood. We studied inbre eding and social structuring of a population of black-railed prairie d ogs (Cynomys ludovicianus) to assess the influence of dispersal and ma ting behavior on patterns of genetic variation. We examined 15 years o f data on prairie dogs, including survival and reproduction, social be havior, pedigrees, and allozyme alleles. Pedigrees revealed mean inbre eding coefficients (F) of 1-2%. A breeding-group model that incorporat ed details of prairie dog behavior and demography was used to estimate values of fixation indices (Estimates). Model predictions were consis tent with the minimization of inbreeding within breeding groups (''cot eries,'' asymptotic F-IL = -0.18) and random mating within the subpopu lation (''colony,'' asymptotic F-IS = 0.00). Estimates from pedigrees (mean F-IL = -0.23, mean F-is = 0.00) and allozyme data (mean F-lL = - 0.21, mean F-IS = -0.01) were consistent with predictions of the model . The breeding-group model, pedigrees, and allozyme data showed remark ably congruent results, and indicated strong genetic structuring withi n the colony (F-LS = 0.16, 0.19 and 0.17, respectively). We concluded that although inbreeding occurred in the colony, the rate of inbreedin g was strongly minimized at the level of breeding groups, but not at t he subpopulation level. The behavioral mechanisms most important to th e minimization of inbreeding appeared to be patterns of male-biased di spersal of both subadults and adults, associated with strong philopatr y of females. Incest avoidance also occurred, associated with recognit ion of close kin via direct social learning within the breeding groups .