Seasonal and lifetime reproductive consequences of inbreeding in the great tit Parus major

Inbreeding depression has been hypothesized to drive the evolution of mating systems and dispersal. Some studies have shown that inbreeding strongly affects survival and/or fecundity, but other studies suggest that fitness consequences of inbreeding are less detrimental or more complex. We studied consequences of mating with a relative in a population of great tits (Parus major) with a high local recruitment rate. Genotypic information from microsatellite markers was used to calculate coefficients of kinship, and fitness was measured as seasonal and lifetime reproductive success. We show that mating with a relative affects seasonal reproductive success, as was found in other studies of the same species. However, these effects do not result in a lifetime fitness reduction, suggesting that individuals may have scope for avoidance of inbreeding after inbreeding depression. Several explanations are proposed as compensatory mechanisms. Although individuals are more likely to divorce after experiencing inbreeding depression, we show that divorce alone cannot explain the compensation for inbreeding depression in subsequent breeding attempts in our study. We conclude that the costs of mating with a relative in the short term do not necessarily imply lifetime fitness consequences. Copyright 2003.