Genetic decline, restoration and rescue of an isolated ungulate population.

Marc‐Antoine Poirier,Jon Jorgenson,Marco Festa‐Bianchet,Fanie Pelletier,David W Coltman

doi:10.1111/eva.12706

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.

Highlights

Theories of genetic drift predict that small and isolated populations will suffer decreased genetic diversity and increased inbreeding over time, eventually compromising population persistence (Charpentier et al, 2005; Da Silva et al, 2009; Grueber, Wallis, & Jamieson, 2008)
Small populations with low genetic diversity are expected to be less likely to adapt to environmental changes due to low evolutionary potential (Vander Wal, Garant, Festa‐Bianchet, & Pelletier, 2012), further increasing risk of extinction
In 2002– 2007, the low and stagnating population size justified the translocation of bighorn sheep from another population to Ram Mountain, providing a rare opportunity to test the effectiveness of translocation for recovery in a wild population undergoing inbreeding depression

Summary

| INTRODUCTION

Theories of genetic drift predict that small and isolated populations will suffer decreased genetic diversity and increased inbreeding over time, eventually compromising population persistence (Charpentier et al, 2005; Da Silva et al, 2009; Grueber, Wallis, & Jamieson, 2008). Small populations with low genetic diversity are expected to be less likely to adapt to environmental changes due to low evolutionary potential (Vander Wal, Garant, Festa‐Bianchet, & Pelletier, 2012), further increasing risk of extinction. Rioux‐Paquette, Festa‐Bianchet, and Coltman (2011) found that inbred female lambs at Ram Mountain suffered a 40% decrease in overwinter survival They found no evidence of inbreeding depression for male lambs and suggested that sex‐differential effects of inbreeding may be a general pattern in sexually dimorphic mammals because of sex‐biased maternal care or sexual differences in early development strategies (Rioux‐Paquette et al, 2011). In 2002– 2007, the low and stagnating population size justified the translocation of bighorn sheep from another population to Ram Mountain, providing a rare opportunity to test the effectiveness of translocation for recovery in a wild population undergoing inbreeding depression. Using detailed yearly demographic and genetic population properties, we present a precise description of both decline and recovery in a wild population of ungulates over four generations (27 years)

| METHODS

| DISCUSSION

Findings

ETHICAL APPROVAL