A heterochronic explanation for the behaviorally polymorphic genus Canis: A study of the development of behavioral differences in dogs (Canis lupus familiaris) and wolves (Canis lupus lupus)
Dogs (Canis lupus familiaris) and wolves (Canis lupus lupus) share genotypes, which are nearly identical, but their behavioral phenotypes are very different. It has been repeatedly hypothesized that these adult behavioral differences are the result of heterochronic changes, or differences during the course of development. This dissertation investigates three major behavioral differences between these two morphs: (1) Interspecies socialization: both dogs and wolves are capable of forming interspecies attachments, most commonly with humans, but wolves require more intense exposure to reach a less intense attachment. (2) Expression of species-typical motor patterns: while dogs and wolves have the same species-typical motor patterns, they express them at different rates and in different frequencies. (3) Frequency of barking: while both dogs and wolves bark, dogs bark at a much higher frequency than wolves. The primary objective of this dissertation is to determine if behavioral differences between polymorphs of the genus Canis are the result of heterochrony.
Fifty-two Canis pups including, both mother- and hand-reared dogs (Canis lupus familiaris) represented by two breeds (Border collies and German shepherds) and hand-reared wolves were observed. Frequency of motor pattern display was recorded from two to eight weeks of age in all groups. Responses of pups to olfactory, auditory, and visual stimuli were also tested weekly from two to seven weeks of age. Groups were then compared on the timing of the onset and frequency of expression of foraging motor patterns (orient, eye, stalk, chase, and grab-bite) and the onset of their ability to orient towards olfactory, auditory, and visual stimuli.
My results demonstrate that small changes in the timing of the critical period of socialization in relationship to the development of the sensory systems do account for differences in the ability to form interspecies social attachments between dogs and wolves. The data also demonstrate that there are heterochronic differences in the development of species typical foraging motor patterns between dogs and wolves. However, these changes alone do not explain the fragmenting of breed-typical sequences in relation to functional wolf sequences.
Investigation of barking frequency was accomplished by searching previous literature to define acoustic measurements, which distinguish the bark from other vocalizations. This definition was then used to determine in what situations the bark occurred in dogs, wild Canis species, other mammals, and birds.
Barking occurs in a large variety of mammals and birds, and is motivated by conflicting internal states associated with mobbing. This is supported by the acoustic structure of the bark itself and the contexts in which mammals, including dogs and other members of the genus Canis, and birds use the bark vocalization.