How does evolutionary evaluation illuminate body size among canids?

In this review, we examine mammalian body size as it reflects life history and genomic composition, with a primary focus on canids and the domestication of the gray wolf. The range of variation in body size is greater among Carnivora than any other terrestrial order. In the Canidae, this range is some 2 orders of magnitude. Macroevolutionary patterns (eg, Bergmann's rule and Cope's rule) that have been proposed in the past often fail to comport with modern studies on this aspect of carnivoran evolution. Clades often begin with small to medium size (mesocarnivorans) and diversify mostly in a right-skewed (larger) direction. The observed variation in body size reflects phenotypic plasticity in response to life history. As with many Mammalia, historically high gene flow (hybridization and introgression) among canid lineages has been a crucial source of genomic variation (nuclear and mitochondrial), yielding the potential for high plasticity of phenotypes such as body size. In addition, epigenetic marks connect genetic expression with environmental conditions in the manifested phenotypes. Among Mammalia generally, a larger size is associated with a longer life span, reflecting the foregoing genomic composition and environmental influences over a long geological time. However, the larger modern domestic dog breeds trend toward shorter life spans. The latter appears to reflect genetically mediated phenotypes that emerged secondary to domestication but nonetheless against a background of broadly and deeply conserved developmental and physiological patterns and body plans.