title: Translating effects of inbreeding depression on component vital rates to overall population growth in endangered bighorn sheep.
abstract: Evidence of inbreeding depression is commonly detected from the fitness traits of animals, yet its effects on population growth rates of endangered species are rarely assessed. We examined whether inbreeding depression was affecting Sierra Nevada bighorn sheep (Ovis canadensis sierrae), a subspecies listed as endangered under the U.S. Endangered Species Act. Our objectives were to characterize genetic variation in this subspecies; test whether inbreeding depression affects bighorn sheep vital rates (adult survival and female fecundity); evaluate whether inbreeding depression may limit subspecies recovery; and examine the potential for genetic management to increase population growth rates. Genetic variation in 4 populations of Sierra Nevada bighorn sheep was among the lowest reported for any wild bighorn sheep population, and our results suggest that inbreeding depression has reduced adult female fecundity. Despite this population sizes and growth rates predicted from matrix-based projection models demonstrated that inbreeding depression would not substantially inhibit the recovery of Sierra Nevada bighorn sheep populations in the next approximately 8 bighorn sheep generations (48 years). Furthermore, simulations of genetic rescue within the subspecies did not suggest that such activities would appreciably increase population sizes or growth rates during the period we modeled (10 bighorn sheep generations, 60 years). Only simulations that augmented the Mono Basin population with genetic variation from other subspecies, which is not currently a management option, predicted significant increases in population size. Although we recommend that recovery activities should minimize future losses of genetic variation, genetic effects within these endangered populations-either negative (inbreeding depression) or positive (within subspecies genetic rescue)-appear unlikely to dramatically compromise or stimulate short-term conservation efforts. The distinction between detecting the effects of inbreeding depression on a component vital rate (e.g., fecundity) and the effects of inbreeding depression on population growth underscores the importance of quantifying inbreeding costs relative to population dynamics to effectively manage endangered populations.
authors: University of Montana, Wildlife Biology Program, College of Forestry and Conservation, Missoula, MT 59812, U.S.A., email heather.johnson@state.co.us.
authors: Heather E
authors: HE
authors: Johnson
authors: University of Montana, Wildlife Biology Program, College of Forestry and Conservation, Missoula, MT 59812, U.S.A.
authors: L Scott
authors: LS
authors: Mills
authors: White Mountain Research Station, University of California, 3000 East Line Street, Bishop, CA 93514, U.S.A.
authors: John D
authors: JD
authors: Wehausen
authors: Sierra Nevada Bighorn Sheep Recovery Program, California Department of Fish and Game, 407 West Line Street, Bishop, CA 93514, U.S.A.
authors: Thomas R
authors: TR
authors: Stephenson
authors: University of Montana, Flathead Biological Station and Division of Biological Sciences, Polson, MT 59860, U.S.A. and the Centro de Investigação em Biodiversidade e Recursos Genéticos and Universidade do Porto (CIBIO-UP), Vairão, Portugal.
authors: Gordon
authors: G
authors: Luikart
mesh_terms: D000818:Animals; D003247:Conservation of Natural Resources; D056727:Endangered Species; D005260:Female; D005298:Fertility; D014644:Genetic Variation; D006579:Heterozygote; D007178:Inbreeding; D008297:Male; D018895:Microsatellite Repeats; D008957:Models, Genetic; D009505:Nevada; D011156:Population Density; D011157:Population Dynamics; D012726:Sexual Behavior, Animal; D012756:Sheep / Q000235:genetics / Q000502:physiology*