Effective Population Size, Genetic Variation, and Their Relevance for Conservation: The Bighorn Sheep in Tiburon Island and Comparisons with Managed Artiodactyls

Abstract

The amount of genetic diversity in a finite biological population mostly depends on the interactions among evolutionary forces and the effective population size (N e) as well as the time since population establishment. Because the N e estimation helps to explore population demographic history, and allows one to predict the behavior of genetic diversity through time, N e is a key parameter for the genetic management of small and isolated populations. Here, we explored an N e-based approach using a bighorn sheep population on Tiburon Island, Mexico (TI) as a model. We estimated the current (N crnt) and ancestral stable (N stbl) inbreeding effective population sizes as well as summary statistics to assess genetic diversity and the demographic scenarios that could explain such diversity. Then, we evaluated the feasibility of using TI as a source population for reintroduction programs. We also included data from other bighorn sheep and artiodactyl populations in the analysis to compare their inbreeding effective size estimates. The TI population showed high levels of genetic diversity with respect to other managed populations. However, our analysis suggested that TI has been under a genetic bottleneck, indicating that using individuals from this population as the only source for reintroduction could lead to a severe genetic diversity reduction. Analyses of the published data did not show a strict correlation between H E and N crnt estimates. Moreover, we detected that ancient anthropogenic and climatic pressures affected all studied populations. We conclude that the estimation of N crnt and N stbl are informative genetic diversity estimators and should be used in addition to summary statistics for conservation and population management planning.

Genetic population structure of Peninsular bighorn sheep (Ovis canadensis nelsoni) indicates substantial gene flow across US–Mexico border

“…Genetic compensation could maintain genetic variation in PBS if certain social behaviors are density dependent. Gasca-Pineda et al (2013) found similar levels of genetic diversity in a bighorn sheep population established from only 16 individuals. These authors suggested that decreased predation pressure may have resulted in less sexual segregation, allowing females to mate with non-dominant males within the herd.…”

Genome‐wide set of SNPs reveals evidence for two glacial refugia and admixture from postglacial recolonization in an alpine ungulate

“…Similarly, depressed genetic diversity can also be seen in island bighorn sheep populations when compared to that of mainland populations (Gasca‐Pineda et al . ). Contemporary observations in other alpine species also tend to find that small isolated populations possess less genetic diversity (Henry et al .…”

Assessing changes in genomic divergence following a century of human‐mediated secondary contact among wild and captive‐bred ducks

“…Although effective population size and genetic diversity are typically associated, previous studies have shown that these two diversity estimates can become uncoupled due to differential gene flow and/or demographic processes (e.g., bottlenecking) acting through time (Gasca-Pineda, Cassaigne, Alonso, & Eguiarte, 2013;Lonsinger, Adams, & Waits, 2018;Miller & Waits, 2003). Given that our study deals with gene flow between wild and domestic lineages, we posit that gene flow from an inbred domestic lineage (e.g., game-farm mallards) can move "novel" variation into a population and thus create a signature of increased or similar effective population size as es- Similarly, we hypothesize that differential gene flow of loci across the genome from game-farm mallards into wild mallards may also explain the increased genomic differentiation observed across time between wild mallards and black ducks (Figure 3; Supplementary Materials Figure S2B Figure 4).…”