Abstract
Conservation biologists have increasingly used translocations to mitigate population declines and restore locally extirpated populations. Genetic data can guide the selection of source populations for translocations and help evaluate restoration success. Bighorn sheep (Ovis canadensis) are a managed big game species that suffered widespread population extirpations across western North America throughout the early 1900s. Subsequent translocation programs have successfully re‐established many formally extirpated bighorn herds, but most of these programs pre‐date genetically informed management practices. The state of Nevada presents a particularly well‐documented case of decline followed by restoration of extirpated herds. Desert bighorn sheep (O. c. nelsoni) populations declined to less than 3,000 individuals restricted to remnant herds in the Mojave Desert and a few locations in the Great Basin Desert. Beginning in 1968, the Nevada Department of Wildlife translocated ~2,000 individuals from remnant populations to restore previously extirpated areas, possibly establishing herds with mixed ancestries. Here, we examined genetic diversity and structure among remnant herds and the genetic consequences of translocation from these herds using a genotyping‐by‐sequencing approach to genotype 17,095 loci in 303 desert bighorn sheep. We found a signal of population genetic structure among remnant Mojave Desert populations, even across geographically proximate mountain ranges. Further, we found evidence of a genetically distinct, potential relict herd from a previously hypothesized Great Basin lineage of desert bighorn sheep. The genetic structure of source herds was clearly reflected in translocated populations. In most cases, herds retained genetic evidence of multiple translocation events and subsequent admixture when founded from multiple remnant source herds. Our results add to a growing literature on how population genomic data can be used to guide and monitor restoration programs.
Highlights
Habitat fragmentation, overharvest, disease, and other human‐influenced processes are driving population declines of many species across the globe, often resulting in widespread population extirpations and putative extinctions (Cameron et al, 2011; Forister, Jahner, Casner, Wilson, & Shapiro, 2011; Lips et al, 2006; Woinarski, Burbidge, & Harrison, 2015)
Our results provide a reference for continued translocation decisions and a baseline for understanding how past and future population responses might relate to genetic variation within and among herds
Emerging technologies that allow for increases in the extent of genomic sampling are reshaping our understanding of the genetic consequences of conservation actions, even for organisms with complicated management histories (Allendorf, Hohenlohe, & Luikart, 2010; Shafer et al, 2015)
Summary
Overharvest, disease, and other human‐influenced processes are driving population declines of many species across the globe, often resulting in widespread population extirpations and putative extinctions (Cameron et al, 2011; Forister, Jahner, Casner, Wilson, & Shapiro, 2011; Lips et al, 2006; Woinarski, Burbidge, & Harrison, 2015). In an effort to repopulate previously occupied mountain ranges, augment genetic variation within isolated remnant herds, and increase connectivity among populations, state and federal agencies developed management programs that conducted several hundred translocations throughout the late 1900s (Wild Sheep Working Group, 2015). As part of this enterprise, the Nevada Department of Wildlife (NDOW) undertook an extensive series of translocations that have spanned five decades (1968‐present), raising the statewide population estimate from less than 3,000 individuals in 1960 to at least 12,000 individuals in 2018 (NDOW, 2001, NDOW unpublished data). Our study illustrates how high‐throughput sequencing approaches can be used to illustrate the population genetic context and consequences of translocation activities spanning several decades
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