Low Persistence of Genetic Rescue Across Generations in the Arctic Fox (Vulpes lagopus)

Abstract

Genetic rescue can facilitate the recovery of small and isolated populations suffering from inbreeding depression. Long-term effects are however complex and examples spanning over multiple generations under natural conditions are scarce. The aim of this study was to test for long-term effects of natural genetic rescue in a small population of Scandinavian Arctic foxes (Vulpes lagopus). By combining a genetically verified pedigree covering almost 20 years with a long-term dataset on individual fitness (n=837 individuals), we found no evidence for elevated fitness in immigrant F2 and F3 compared to native inbred foxes. Population inbreeding levels showed a fluctuating increasing trend and emergence of inbreeding within immigrant lineages shortly after immigration. Between 0-5 and 6-9 years post immigration, the average population size decreased by almost 22 % and the average proportion of immigrant ancestry rose from 14 % to 27 %. Y chromosome analysis revealed that two out of three native male lineages were lost from the gene pool, but all founders represented at the time of immigration were still contributing to the population at the end of the study period through female descendants. The results highlight the complexity of genetic rescue and suggest that beneficial effects can be brief. Continuous gene flow may be needed for small and threatened populations to recover and persist in a longer time perspective.

Genomic and fitness consequences of inbreeding in an endangered carnivore

“…These results however imply a different pattern, as genomic inbreeding (F ROH ) in fact increased to similar levels as before immigration within two to three generations, at least in two out of four individuals. This in combination with no detected fitness elevation beyond immigrant F1 generation (Lotsander et al, 2021) thus highlight the transient nature of genetic rescue. This result is in line with Saremi et al (2019) who observed long tracts of homozygosity in a Florida panther descended from translocated individuals.…”

“…In our case, immigration was comprised of only three individuals (of which two were full siblings) entering a small and fluctuating population. During recent years, close inbreeding within immigrant lineages has been recorded, potentially resulting in a genetic sweep (Lotsander et al, 2021). Additional gene flow into the population is needed to maintain beneficial effects of outcrossing.…”

“…The parents of the immigrant brothers were born within the captive breeding programme but had ancestry from five different subpopulations through grandparents and great grandparents (Figure 1). The immigrants produced at least 63 offspring in total (Lotsander et al, 2021), and 5 years after immigration, genetic rescue was evident through 1.9 times higher survival and 1.3 times higher breeding success in immigrant F1 offspring compared to native ones (Hasselgren et al, 2018). During the same time period, the population increased from 26 to 58 breeding individuals.…”

“…This is an effective method to detect survivors as arctic foxes utilize the same dens every year rather than creating new ones (Dalerum et al, 2002). Juveniles were ear‐tagged with unique colour combinations and first year survival was based on visual observations and genetic assignment (Hasselgren et al, 2018; Lotsander et al, 2021; Norén et al, 2016). Individuals that were visually or genetically verified at least 1 year after they were born were classified as first year survivors.…”

“…Recently, an event of natural immigration by three outbred males, of which two were brothers, resulted in genetic rescue through elevated fitness in F1 offspring between immigrants and native individuals. However, no increase in fitness was detected in F2 or F3 offspring with immigrant ancestry (Hasselgren et al, 2018; Lotsander et al, 2021). Moreover, no significant difference in microsatellite heterozygosity before versus after immigration was found (Hasselgren et al, 2018).…”