Inbreeding depression across the lifespan in a wild mammal population

Significance Inbreeding depression is the decrease in fitness with increased genome-wide homozygosity that occurs in the offspring of related parents. Estimation of its effect in wild populations has been challenging, and while evidence of inbreeding depression in juvenile traits is widespread, examples during later life stages remain rare. Here, in a species with extended maternal care, genomic inbreeding coefficients, but not pedigree-based ones, revealed inbreeding depression in annual breeding success in both sexes, and in offspring rearing success in females. This contributed to inbreeding depression in estimates of lifetime fitness in both sexes. Our work illustrates that inbreeding depression in adult traits can be as large as in juvenile traits but requires more powerful methods to be detected.