Inbreeding Depression and Genetic Rescue in a Critically Endangered Carnivore

Harmful effects arising from inbreeding is a long-standing observation that is well founded in theory. Empirical evidence in natural populations is however rare because of the challenges of assembling pedigrees supplemented with fitness traits. Furthermore, effects of gene flow on fitness and population growth (genetic rescue) in inbred populations is another aspect that is difficult to document under natural conditions. Here, we use a combination of genetically verified pedigree and analysis of fitness during a 15 years to investigate the occurrence of inbreeding depression and subsequent genetic rescue arising from immigration into a critically endangered and bottlenecked arctic fox (Vulpes lagopus) population in Sweden. Results show high levels of inbreeding and severe inbreeding depression affecting fundamental fitness traits during a period of isolation. Immigration by three unrelated males however reduce inbreeding levels significantly and first-generation outbred individuals display higher fitness than inbred individuals. During the same time period, the population undergo a pronounced increase in size. Based on this, we test the consequences of inbreeding and genetic rescue on individual fitness and population demography.