Biological Exuberance: Animal Homosexuality and Natural Diversity

Frederick, H., and C. N. Johnson (1996) “Social Organization in the Rufous Bettong, Aepyprymnus rufescens.” Australian Journal of Zoology 44:9–17.

Ganslosser, U. (1993) “Stages in Formation of Social Relationships—an Experimental Investigation in Kangaroos (Macropodoidea: Mammalia).” Ethology 94:221-47.

*———(1979) “Soziale Kommunikation, Gruppenleben, Spiel- und Jugendverhalten des Doria-Baumkanguruhs (Dendrolagus dorianus Ramsay, 1833) [Social Communication, Group Life, and Play Behavior of Doria’s Tree Kangaroo].” Zeitschrift fur Saugetierkunde 44:137–53.

*Ganslosser, U., and C. Fuchs (1988) “Some Quantitative Data on Social Behavior of Rufous Rat-Kangaroos (Aepyprymnus rufescens Gray, 1837 (Mammalia: Potoroidae)) in Captivity.” Zoologischer Anzeiger 220:300–312.

George, G. G. (1977) “Up a Tree with Kangaroos.” Animal Kingdom 80(2):20– 24.

*Hutchins, M., G. M. Smith, D. C. Mead, S. Elbin, and J. Steenberg (1991) “Social Behavior of Matschie’s Tree Kangaroo (Dendrolagus matschiei) and Its Implications for Captive Management.” Zoo Biology 10:147–64.

Jarman, P. J. (1991) “Social Behavior and Organization in the Macropodoidea.” Advances in the Study of Behavior 20:1–50.

*Johnson, P. M. (1980) “Observations of the Behavior of the Rufous Rat-Kangaroo, Aepyprymnus rufescens (Gray), in Captivity.” Australian Wildlife Research 7:347–57.

IDENTIFICATION: A bearlike marsupial with woolly brown or gray fur, large black nose, white chest, and long claws. DISTRIBUTION: Eastern and southeastern Australia. HABITAT: Eucalyptus forests. STUDY AREAS: Lone Pine Sanctuary, Brisbane, Australia; San Diego Zoo; subspecies P.c. adustus.

Social Organization

Koalas are largely nocturnal and solitary, although in some populations they tend to live in scattered clusters of two to six females with several males. The mating system is probably promiscuous or polygamous (animals mate with multiple partners), and males take no part in raising their young.

Description

Behavioral Expression: Female Koalas in heat sometimes mount each other in the trees: while one female clings vertically to the trunk, another climbs behind her and reaches around to simultaneously hold on to the tree. She begins to make pelvic thrusts against the other female, while also typically gripping the other female’s neck in her teeth (as does the male during heterosexual mounting). Occasionally one female mounts another from the side (a position sometimes also used by younger males). Usually the mounted female does not display the receptive posture (which involves arching her back while throwing her head back), and homosexual mounts are generally briefer than heterosexual ones. Like male-female copulations, homosexual interactions sometimes involve aggression between the participants: one female may attack the other or pin her to the ground following a mounting. Sometimes two females take turns mounting each other, and homosexual mounting is often interspersed with other signs of intense sexual arousal, including chasing, bellowing, and jerking. BELLOWING is an extraordinary call (also made by males) that has been described as a combination of rasping, growling, wheezing, grunting, rumbling, and braying. It consists of a long series of in-drawn, snorelike breaths alternating with exhalated, belchlike sounds. JERKING is a display resembling the hiccups, in which the female simultaneously jerks her body upward and flicks her head backward repeatedly. Male Koalas also sometimes mount each other, and a few even perform the jerking display like females in heat.

A female Koala mounting another female

Frequency: In captivity, same-sex mounting accounts for 11 percent of all copulatory activity, with the majority of this being mounts between females.

Orientation: Koalas that participate in homosexual mounting are probably bisexual, since females that mount other females have also been observed mating with males.

Nonreproductive and Alternative Heterosexualities

Heterosexual relations in Koalas are marked by a striking amount of aggression and violence: more than two-thirds of fights are between males and females rather than between males. Females are sometimes “pestered” by males that persistently follow, touch, bite, or snap at them; if the female returns the bites, the encounter can escalate into a severe fight. Males have been known to brutally attack females—including pregnant and nursing mothers—knocking them from the trees and savagely mauling them. In fact, it is typical for males to nip females on the neck during mating, and for heterosexual copulations to end with the male attacking the female. Females also fight with males (though less violently), and aggressiveness toward males is considered to be a defining feature of estrus for female Koalas. Occasionally adults are also abusive toward babies: mothers sometimes bite their young, while males have been observed attacking infants that interrupt them during a mating with their mother. Many heterosexual interactions are nonprocreative, since males often try to mount females who are not in heat. Although the females typically rebuff their advances, in some cases the males are able to mount them, often thrusting against the female and ejaculating on her without any penetration. Females in heat also sometimes mount males (REVERSE mounts).

Many wild populations of Koalas have particularly high rates of female infertility (and significantly reduced reproductive rates) due to venereal disease. More than half of all females in some areas are infected with genital chlamydia, a bacteria that causes a number of reproductive tract diseases and, ultimately, sterility. This pathogen has apparently been present in Koala populations for a relatively long time, as records of the associated diseases date back to at least the 1890s. Although the exact mode of its transmission is not yet fully understood, two routes have been implicated: sexual and mother-to-young. The latter may be due to the infant Koala’s habit of eating its mother’s feces directly from her anus during weaning, since she produces a special form of excrement known as PAP especially for feeding her young (this practice is also found in a number of other marsupials).

Other Species

In another marsupial, the Common Brushtail Possum (Trichosurus vulpecula), intersexuality or hermaphroditism occasionally occurs: one individual, for example, had male body proportions, coloring, and genitals combined with mammary glands and a pouch.

Sources

*asterisked references discuss homosexuality/transgender

Brown, A. S., A. A. Girjes, M. F. Lavin, P. Timms, and J. B. Woolcock (1987) “Chlamydial Disease in Koalas.” Australian Veterinary Journal 64:346-50.

*Gilmore, D. P. (1965) “Gynandromorphism in Trichosurus vulpecula.” Australian Journal of Science 28:165.

Lee, A., and R. Martin (1988) The Koala: A Natural History. Kensington, Australia: New South Wales University Press.

Phillips, K. (1994) Koalas: Australia’s Ancient Ones. New York: Macmillan.

*Sharman, G. B., R. L. Hughes, and D. W. Cooper (1990) “The Chromosomal Basis of Sex Differentiation in Marsupials.” Australian Journal of Zoology 37:451–66.

Smith, M. (1980a) “Behavior of the Koala, Phascolarctos cinereus (Goldfuss) in Captivity. III. Vocalizations.” Australian Wildlife Research 7:13–34.

*———(1980b) “Behavior of the Koala, Phascolarctos cinereus (Goldfuss) in Captivity. V. Sexual Behavior.” Australian Wildlife Research 7:41–51.