Tuesday, October 15, 2013

Elephant Artifacts: Vestigial Temporal Glands

By Lisa Barrett

Elephants have two specialized areas on their face called temporal glands. They lie on either side of the head between the eye the ear. From Sophie’s previous blog entry, we know that male elephants go into a state of musth (triggered by the presence of females) during which they secrete a pungent liquid from this gland. It is no surprise, then, that both African and Asian male elephants possess these glands. But why do female elephants also possess these glands?

 A male elephant in musth secretes a pungent liquid from his temporal gland.

First, what is a temporal gland? It is a multi-lobed sac that secretes a viscous, pungent liquid, and it is indicated by a small hole on the face. Male elephants release temporal grand secretions in great quantities, especially when they are excited or under stress. This suggests that the gland is under autonomic control.

Left: The temporal gland structures (modified from Shoshani J., 1992) and microscopic structure (x 40). Right: The location of the opening of the temporal gland.

You may recall that elephants sweat only around their toenails, because they do not possess sweat glands like we do. Interestingly, temporal glands serve as modified apocrine sweat glands. They produce an oily secretion containing cholesterol, phenol, and cresol when the animal is excited or anxious.

A temporal gland can weigh up to 3 kg in males, and it usually weighs no more than 1 kg in females. The glands may secrete throughout the year, but they become especially active in bulls during mating season. Ancient tradition claimed that there were pearls in the elephant’s skull, because the gland’s oozing fluid sometimes appears like crystals. The secretion was also considered to be an antidote for poison, an aphrodisiac, an antiseptic, and a tonic for hair growth!

Elephants in the wild have been observed rubbing their cheeks on trees and other objects in the forest, which suggests a more specific communicative function for the temporal gland secretion. The secretions may serve to mark important locations, like waterholes, or they may contribute to the spacing of the male population.

Elephants smell each others’ temporal glands as part of chemical communication.

While it is relatively well-known that female African elephants produce secretions when they excitedly reunite with members of other herds, the significance of temporal gland secretions in female Asian elephants is still a mystery. In fact, the temporal glands in female Asian elephants are nonsecretory and vestigial. Could they still serve as important signals to conspecifics? Taken together with observations of elephants rubbing their cheeks on trees, females’ production of important chemical information could have broader communicative implications for Asian elephants.

Brown RE (1985) in Social Odours in Mammals, eds Brown RE , Macdonald DW (Oxford Univ Press, New York), Vol 1, pp 235–244.