Genetic consequences of restricted dispersal and incest avoidance in a cooperatively breeding wren

Can restricted dispersal in a family-structured population produce conditions that favor the evolution of helping behavior by kin selection? To address this question a numerical model of a population of cooperatively breeding stripe-backed wrens (Campylorhynchus nuchalis) was developed. The model incorporated the demography and social dynamics of a natural population under long-term study in Venezuela. Replicated simulations followed uniquely labelled copies of alleles for 100 annual cycles, in order to estimate coefficients of kinship between mates and between helpers and the young they raised in relation to overall levels of inbreeding in the population. The consequences of restricted dispersal and incest avoidance were investigated, under different rates of migration. The results indicated that close incest occurred too infrequently to influence genetic structure significantly. Restricted dispersal, on the other hand, even in combination with relatively high rates of immigration (10–20%), like those observed in the natural population, tended to produce genetically viscous populations. Relatedness between mates was significantly greater than 0, and relatedness among members of different groups decreased with distance. The relatedness between mates tended to increase both the relatedness of individuals to their own progeny and the relatedness of helpers to the young they raised. The latter effect predominated, so the genetic consequences of restricted dispersal, in relation to the overall level of inbreeding, tended to favor the evolution of helping by kin selection. Mutually reinforcing consequences of short-range dispersal, on the one hand, and delayed dispersal, on the other, could thus result in accelerating evolution of cooperative breeding.