Studies on the Chemistry and Social Significance of Chin Gland Secretions in the Desert Tortoise, Gopherus agassizii

The chemical structure and biological functions of chin gland secretions were examined in a group of captive desert tortoises, Gopherus agassizii, housed at the Desert Tortoise Conservation Center near Las Vegas, Nevada. Monthly measurements of the chin glands of 20 adult males were made over one year. Gland volume varied seasonally, reaching a maximum in late summer. The chin glands of socially dominant males tended to be larger than those of socially subordinate males. Among all males, there was a positive correlation between plasma testosterone levels and size of the chin glands. Behavioral experiments demonstrated that tortoises of both sexes discriminate the chin gland secretions of familiar males from those of unfamiliar males, suggesting that chin gland secretions may function in conspecific recognition. Electrophoretic studies of chin gland secretions revealed the presence of 12-17 protein components ranging in size from 25,000115,000 Daltons. Although banding patterns among males were very similar, slight individual differences existed in the number and size of high molecular weight protein components.