Genetic decline, restoration and rescue of an isolated ungulate population

Abstract

Isolation of small populations is expected to reduce fitness through inbreeding and loss of genetic variation, impeding population growth and compromising population persistence. Species with long generation time are the least likely to be rescued by evolution alone. Management interventions that maintain or restore genetic variation to assure population viability are consequently of significant importance. We investigated, over 27 years, the genetic and demographic consequences of a demographic bottleneck followed by artificial supplementation in an isolated population of bighorn sheep (Ovis canadensis). Based on a long‐term pedigree and individual monitoring, we documented the genetic decline, restoration and rescue of the population. Microsatellite analyses revealed that the demographic bottleneck reduced expected heterozygosity and allelic diversity by 6.2% and 11.3%, respectively, over two generations. Following supplementation, first‐generation admixed lambs were 6.4% heavier at weaning and had 28.3% higher survival to 1 year compared to lambs of endemic ancestry. Expected heterozygosity and allelic diversity increased by 4.6% and 14.3% after two generations through new alleles contributed by translocated individuals. We found no evidence for outbreeding depression and did not see immediate evidence of swamping of local genes. Rapid intervention following the demographic bottleneck allowed the genetic restoration and rescue of this bighorn sheep population, likely preventing further losses at both the genetic and demographic levels. Our results provide further empirical evidence that translocation can be used to reduce inbreeding depression in nature and has the potential to mitigate the effect of human‐driven environmental changes on wild populations.

Genetic diversity, relatedness and inbreeding of ranched and fragmented Cape buffalo populations in southern Africa

“…Potential concerns about outbreeding depression and/or genomic swamping of the AENP buffalo population following this proposed genetic supplementation could be alleviated by considering the current support for an estimated short time since isolation (~100 years) [ 17 , 49 ] and by conducting regular genetic monitoring of the population. Furthermore, recent studies showed local genes, and alleles related to local adaptation, were maintained in the recipient population after genetic supplementation, while the benefits of genetic rescue were still observed [ 50 – 52 ].…”

Life history, climate and biogeography interactively affect worldwide genetic diversity of plant and animal populations

“…Although expected heterozygosity may be slower at responding to recent demographic setbacks than allelic richness, it is less sensitive to difference in sample size. Moreover, recent longitudinal studies have shown that H E is sensitive to anthropogenic disturbance, and that significant reductions in expected heterozygosity can be observed several generations after a population bottleneck 109 , 110 . For example, a South-African lion population suffered a 10–13% reduction in expected heterozygosity as compared to museum samples collected 100 years earlier (ca.…”

“…To test for spatial autocorrelation, we used an autocorrelogram approach assessing the relationship between Moran’s I of model residuals and pairwise geographical distance 109 . We did not find evidence for patterns of spatial autocorrelation neither for the animal kingdom model nor for the plant kingdom model (Supplementary Fig.…”

Long‐term studies of bighorn sheep and mountain goats reveal fitness costs of reproduction

“…Numbers declined rapidly in 1997–2001, partly because of cougar ( Puma concolor ) predation (Festa‐Bianchet et al, ), then stagnated at about 40 for several years. Thirty‐two sheep were transplanted to Ram Mountain between 2003 and 2015, from a population about 130 km to the north–west (Poirier, Coltman, Pelletier, Jorgenson, & Festa‐Bianchet, ). Trophy hunting ended in 2010 (Pigeon, Festa‐Bianchet, Coltman, & Pelletier, ); 64 males were shot between 1972 and 2007.…”