Elucidating the genetic basis of fitness-related traits is a major goal of molecular ecology. Traits subject to sexual selection are particularly interesting, as non-random mate choice should deplete genetic variation and thereby their evolutionary benefits. We examined the genetic basis of three sexually selected morphometric traits in bighorn sheep (Ovis canadensis): horn length, horn base circumference, and body mass. These traits are of specific concern in bighorn sheep as artificial selection through trophy hunting opposes sexual selection. Specifically, horn size determines trophy status and, in most North American jurisdictions, if an individual can be legally harvested. Using between 7,994–9,552 phenotypic measures from the long-term individual-based study at Ram Mountain (Alberta, Canada), we first showed that all three traits are heritable (h2 = 0.15–0.23). We then conducted a genome-wide association study (GWAS) utilizing a set of 3,777 SNPs typed in 76 individuals using the Ovine Infinium® HD SNP BeadChip. We found suggestive association for body mass at a single locus (OAR9_91647990). The absence of strong associations with SNPs suggests that the traits are likely polygenic. These results represent a step forward for characterizing the genetic architecture of fitness related traits in sexually dimorphic ungulates.

Miller_et_al_Animals_with_phenos_transposedPLINK tped file for individuals used in GWAS analysesMiller_et_al_Animals_with_phenos_transposedPLINK tfam file for individuals used in GWAS analysesMiller_et_al_Base_Circ_Typed_IDs_Only_No_DupesPhenotype file with only 1 measure per individual for setting "base model" in RepeatABELMiller_et_al_Base_Circ_Typed_IDs_OnlyRepeated measures of horn base circumference for sheep used in GWAS analysesMiller_et_al_Length_Typed_IDs_OnlyRepeated measures of horn length for sheep used in GWAS analysesMiller_et_al_Mass_Typed_IDs_OnlyRepeated measures of body mass for sheep used in GWAS analysesMiller_et_al_RepeatABLE_GWAS_ScriptR script for conducting GWAS analyses with the RepeatABLE package