| Summary: | Isolation at small population size can reduce individual fitness and impede population growth caused by inbreeding and genetic drift (i.e. inbreeding depression). Inbreeding depression can however be circumvented by gene flow from unrelated individuals through masking of recessive deleterious alleles and contribute to population persistence (i.e. genetic rescue). Studying these processes in natural populations across generations and under fluctuating environmental conditions however comes with major challenges. Several gaps in the knowledge thus remain regarding causes and consequences of inbreeding depression and genetic rescue in the wild. Using long term data on life history traits, combined with traditional population genetics and novel genomic techniques, we explored the dynamics of inbreeding and gene flow in the highly fragmented arctic fox (Vulpes lagopus) population in Sweden. This thesis mainly focused on the southernmost subpopulation (Helagsfjällen), previously documented to suffer from inbreeding depression. Construction of a genetically verified pedigree (Chapter I and II) revealed that gene flow from three outbred male foxes released from a captive breeding station in Norway resulted in genetic rescue, expressed as elevated first year survival and breeding success in immigrant first generation offspring (F1; Chapter I). However, the rescue effect likely only lasted for one single generation, as we found no selective advantage in later descendants of immigrants (Chapter II and IV). Whole genome sequencing of a subset of individuals from the same subpopulation showed that some immigrant F2 and F3 individuals were highly inbred despite the recent outbreeding events (Chapter III). Identification of putative deleterious variation within coding regions suggested that the immigrants introduced a large number of strongly deleterious alleles which were absent from the native gene pool (Chapter IV and V). Expression of the deleterious variation introduced may explain the low persistence of genetic rescue. ...
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