The influence of genetics on horn size in bighorn sheep

  • Author / Creator
    Reich, Miranda H
  • Headgear are cranial appendages usually seen in males of infraorder Pecora. This trait is used to determine hierarchy and gain access to mates. In bighorn sheep, males or rams have impressively large horns that are made of keratin and cancellous bone. These horns are used in yearly combats to determine access to females. The aim of this thesis was to better understand the role of genetics in horn size. This aim was addressed by reviewing the literature and analyzing horn data from National Bison Range in Montana, USA. I reviewed studies about intraspecific variation and functional genetics of headgear, which were then synthesized to make general conclusions and identify gaps in our knowledge of the genetics of headgear. The results of the literature review were antler and horn size are a heritable trait, heterozygosity-fitness correlations are hard to detect in both Cervids and Bovids, and several genes are associated with both antlers and horns. Based on the literature review, I was able to hypothesize that horn size is a heritable trait, horn size has a lot of genetic variation, and horn size should be affected by a heterozygosity-fitness correlation. These hypotheses were tested in my empirical study by using horn measurements for 114 rams and linear mixed effects models to test for the effects of genetic diversity on horn size. This study found that year 3 annuli length was highly heritable, heterozygosity explains some of the variation in horn size, and age or annuli number explains most of the variation found in horn size. At the end of the study, I found that horn size is a heritable trait. In addition, heterozygosity was a significant source of variation for horn length, horn mass, and annuli length on its own, but its role was diminished when age or annuli number was also in the model. Inbreeding coefficients on the other hand was an insignificant source of variation for any horn measurement looked at. This means a ram’s yearly growth rate or age is a better predictor of a ram’s horn size than heterozygosity or inbreeding coefficients and there might be an HFC for longevity or survival. Both the literature review and the empirical study indicate that our understanding of intraspecific variation and the genetics of Pecoran headgear is limited. Some remaining questions are what is the quantitative genetic architecture of headgear size, do wild species have the same intraspecific variation or different intraspecific variation as domestic species, and does heterozygosity or the homozygosity evaluated by inbreeding coefficients affect horn size.

  • Subjects / Keywords
  • Graduation date
    Fall 2021
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.