Investigating the genetic and environmental architecture of interpack aggression in North American grey wolves.

Aggression confers several fitness benefits including increased breeding opportunities and resource acquisition. Determining the relative contributions of genetic and environmental components to shaping aggression is essential for advancing our understanding of how selection affects the distribution of aggressive phenotypes in a population. In a From the Cover article in this issue of Molecular Ecology, vonHoldt et al. (2020) used RAD-seq methods to obtain genome-wide single nucleotide polymorphism (SNP) data to estimate heritability of interpack aggression of 141 North American grey wolves (Canis lupus) surveyed from 1995-2018. The authors inferred heritability using both a SNP-based genetic relationship matrix (GRM) and a consensus pedigree informed by: (a) previously obtained microsatellite data; (b) past observations of parentage; and (c) statistical reconstruction of parent-offspring pairs. SNP-based (i.e., GRM) and pedigree-based (i.e., consensus pedigree) heritability estimates were 37% and 14%, respectively, with an additional 14%-16% explained by natal pack effects. The study confirmed the previously discovered strong effects of relative pack size and breeding status on interpack aggression, illustrating how social dynamics and density-dependent factors induce variance in aggressive behaviours. Finally, the authors found associations between average individual aggression scores (IAS) and specific candidate genes (MY09A and TRAK1). In sum, vonHoldt et al. (2020) provides an unprecedented and nuanced synthesis that not only suggests gene-aggression associations, but also emphasizes how additive genetic variance and density-dependent factors interact to maintain phenotypic variance in aggression over time.