Conservation genetics of reintroduced California bighorn sheep in Oregon

Zachary H Olson, Purdue University

Abstract

Bighorn sheep (Ovis canadensis) historically occupied North American alpine habitats in great numbers from the Baha Peninsula north into Alberta and British Columbia, Canada. Unfortunately, like most big game species in North America, bighorn sheep experienced a period of exploitation following European settlement that resulted in massive range declines and extirpations. Reintroduction efforts for bighorn sheep began as early as the 1920’s in British Columbia and continue today throughout most of the mountain west. As a result of this massive conservation effort, over 50% of current mountain sheep populations are derived from translocations. Natural metapopulations of mountain sheep historically were characterized by the patchy distribution of suitably-rugged habitat and exhibited relatively common extinctions of and movement between populations. However, the genetic and demographic benefits associated with migrants are unavailable to many extant bighorn sheep populations because reintroduction efforts have yet to establish populations within dispersal range or because traditional migration corridors have been bisected by human development. Thus, despite the overwhelming success of reintroduction efforts for bighorn sheep in general, many reintroductions fail and some reintroduced populations have experienced decreased productivity possibly as a result of inbreeding depression. Genetic management is one possible option to mitigate the small-population problems associated with reintroduced bighorn sheep. This research endeavored to assess the efficacy of genetic management as a tool for the conservation of reintroduced populations of bighorn sheep. First, I conducted a review of the literature reporting research on mountain sheep in North America that incorporated the use of molecular markers. Second, I used the data from a suite of molecular markers developed from my literature review to assess the genetic effects of a replicated, experimental supplementations designed to increase genetic diversity and herd productivity. Further, I incorporated demographic simulations to assess the risk of outbreeding depression as a result of the experimental supplementations. This assessment demonstrated the success of genetic management by documenting interpopulation hybrids, identifying no evidence for outbreeding depression as a result of contact between the genetically distinct resident and supplemented populations, and by identifying increased population-level metrics of genetic diversity in post-supplementation populations compared with pre-supplementation levels. Third, I quantified the effects of different translocation histories on the genetic diversity of bighorn sheep populations. Reintroduced populations that received individuals deriving from more than one sampling event on a source population exhibited the highest genetic diversity and populations forced through multiple genetic bottlenecks exhibited the lowest genetic diversity. Fourth, I used herd-inventory data from Oregon’s bighorn sheep to determine if populations of bighorn sheep exhibited a demographic response to experimental genetic management. I identified positive, but different responses to genetic management in replicate populations.

Degree

Ph.D.

Advisors

Rhodes, Purdue University.

Subject Area

Wildlife Management|Genetics

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