Effects of genetic management on reproduction, growth, and survival in captive endangered pygmy rabbits (Brachylagus idahoensis)

Abstract

A quarter of all lagomorph species worldwide are threatened with extinction. Captive breeding programs, such as that developed for the Columbia Basin (CB) pygmy rabbit (Brachylagus idahoensis), sometimes are implemented as emergency conservation measures to restore small, genetically distinct populations. However, small source populations also may have low genetic diversity, which may influence attributes related to fitness, including growth, survival, and reproduction. We used mixed-effects regression models to explore the influence of genetic pedigree (% CB) on pairing success, growth, and survival during the 10-year captive breeding program at Washington State University, which included controlled pairings and outbreeding with pygmy rabbits from Idaho. Pairing success, juvenile growth, and juvenile survival declined with increasing CB pedigree of 1 or both parents, suggesting inbreeding depression among the small number of related founders. Demographic variables such as age, sex, and previous pregnancies, and environmental variables such as month and temperature at birth also were associated with production of pygmy rabbits. Our study illustrates the difficulty of retaining a unique genome of a small source population while simultaneously producing enough rabbits for restoration into natural habitat as part of endangered species recovery programs.

Consequences for conservation: population density and genetic effects on reproduction of an endangered lagomorph

“…The average number of litters per female that we documented matched closely to those reported from breeding in captivity by Elias et al. (), although we were unable to assign every kit to a litter based on their weight. Dividing the average number of kits by the average number of litters per female in our study yielded an average of 3.0 emerged kits per litter.…”

“…After initial low reproductive output and survival, pygmy rabbits from Idaho were incorporated into the captive population in 2003 to counteract inbreeding depression (USFWS , Elias et al. ). In captivity, males and females were paired strategically for breeding to maximize the genetic diversity of the resulting offspring (WDFW ).…”

“…Because kits from the same litter were captured at different times throughout the capture period, we used two previously constructed growth curves for pygmy rabbits (Estes‐Zumpf and Rachlow , Elias et al. ) to estimate the date of birth for each kit and group kits from the same mother into litters. When assigning kits to litters, we took into account a 22–25 d gestation period between litters (Elias et al.…”

“…, Elias et al. ). Population density can interact with genetic diversity to influence reproductive output; high densities create a stressful environment that can alter the expression and fitness costs of low genetic diversity (Armbruster and Reed , Fox and Reed , Reed et al.…”

“…We expected individuals with high amounts of Washington ancestry to have relatively low reproductive output because of a history of inbreeding depression in the population (Elias et al. ). Alternately, individuals with high Washington ancestry might show relatively high reproductive output due to local adaptations not found in individuals from other sources.…”