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Heritability of Horn Size in Thinhorn Sheep - PubMed

  • ️Tue Jan 01 2019

Heritability of Horn Size in Thinhorn Sheep

Zijian Sim et al. Front Genet. 2019.

Abstract

Understanding the genetic basis of fitness-related trait variation has long been of great interest to evolutionary biologists. Secondary sexual characteristics, such as horns in bovids, are particularly intriguing since they can be potentially affected by both natural and sexual selection. Until recently, however, the study of fitness-related quantitative trait variation in wild species has been hampered by a lack of genomic resources, pedigree, and/or phenotype data. Recent innovations in genomic technologies have enabled wildlife researchers to perform marker-based relatedness estimation and acquire adequate loci density, enabling both the "top-down" approach of quantitative genetics and the "bottom-up" approach of association studies to describe the genetic basis of fitness-related traits. Here we combine a cross species application of the OvineHD BeadChip and horn measurements (horn length, base circumference, and volume) from harvested thinhorn sheep to examine the heritability and to perform a genome-wide single-nucleotide polymorphism association study of horn size in the species. Thinhorn sheep are mountain ungulates that reside in the mountainous regions of northwestern North America. Thinhorn sheep males grow massive horns that determine the social rank and mating success. We found horn length, base circumference, and volume to be moderately heritable and two loci to be suggestively associated with horn length.

Keywords: Genome-Wide Association Study; fitness-related trait; heritability; horn size; thinhorn sheep.

Copyright © 2019 Sim and Coltman.

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Figures

Figure 1
Figure 1

Map of study area. Shaded region represents region in southwest Yukon where the samples originated.

Figure 2
Figure 2

Pictures showing the horn measurement process: (A) Total horn length measurement, (B) horn base circumference, (C) marking of annuli to determine age, and (D) example of horn with broken/worn lamb tip. Note that horns in (A), (B), and (C) are considered full-curl. (Image courtesy of Yukon Ministry of Environment.)

Figure 3
Figure 3

Plots of horn size traits as function of age class.

Figure 4
Figure 4

Manhattan plots for associations between SNPs and each of three horn size traits: horn length, horn base circumference, and horn volume. The black line represents the threshold for genome-wide significance, and red line represents suggestive significance. The two labeled loci are of suggestive significance for horn length.

Figure 5
Figure 5

Q-Q plots for each horn size trait with the genome inflation factor and standard error printed on the bottom right corner of each plot. The black line represents a 1:1 correspondence, while the red line is a regression through the observed data.

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