Bergman's Rule & Antler Allometry in Nearctic & Neotropical White-tailed deer (Odocoileus virginianus)

White-tailed deer evolved in cold climates in North America. In such environments, it is selectively advantageous to have a larger body size that retains heat. Antlers, a secondary-sex characteristic of adult males, are proportionately larger in larger animals, an example of allometry. As the deer spread south into Central and South America, the climate becomes progressively warmer and the selective advantage is to those subspecies with small bodies that radiate heat. Antlers become proportionately smaller, and in some subspecies are reduced to mere spikes. Both of the animals above are mature adults. The inverse relation between latitude and body size is an example of Bergman's Rule.