Ancestral inbreeding only minimally affects inbreeding depression in mammalian populations.

Inbreeding depression can be reduced, or purged, by selection against deleterious alleles. This prediction is the basis of the recommendation that captive wildlife populations suffering from inbreeding depression be intentionally bred from healthy inbred animals. Yet data on the effectiveness of purging inbreeding depression are few. In this study I present and use two different regression models (an ancestral inbreeding model and a lethal recessive model) to test for the presence of purging effects in 25 captive mammalian populations. Fitness components examined were neonatal survival, survival from neonate to weaning, and litter size. In only one species was purging statistically significant. However, 15 of 17 species that showed inbreeding depression exhibited a slight decline in inbreeding depression in neonatal survival among descendants of inbred animals. These results show a small but highly significant trend of purging on neonatal survival. No trends in purging effects were observed in weaning survival or litter size. The effects were not likely to be strong enough to be of practical use in eliminating inbreeding depression.