Too big to purge: persistence of deleterious mutations in island populations of the European barn owl (Tyto alba)

Abstract An important aspect of assessing endangered levels and managing conservation is the study of inbreeding status, identifying its origin as well as assessing the mutation load in wild populations. In this study, we used 502 barn owls from continental and island populations across Europe. In addition to comparing inbreeding status, we determined whether inbreeding is due to non-random mating or high co-ancestry within the population. We show that islands have higher levels of inbreeding than continental populations, and that this is mainly due to small effective population sizes rather than recent consanguineous mating. We assess the probability that a region is autozygous along the genome and show that this probability decreased as the number of genes present in that region increased. Finally, we looked for evidence of reduced selection efficiency and purging in island populations. Among island populations, we found an increase in numbers of both neutral and deleterious minor alleles, possibly as a result of drift and decreased selection efficiency but we found no evidence of purging.