Same-sex behavior seen in nearly all animals
Jun 16, Biology/Other
Full size image This photo shows a female-female pair of Laysan Albatross. Females cooperatively build nests and rear young when males are scarce. Credit: Eric VanderWerf. Same-sex behavior is a nearly universal phenomenon in the animal kingdom, common across species, from worms to frogs to birds, concludes a new review of existing research.
"It's clear that same-sex sexual behavior extends far beyond the well-known examples that dominate both the scientific and popular literature: for example, bonobos, dolphins, penguins and fruit flies," said Nathan Bailey, the first author of the review paper and a postdoctoral researcher in the Department of Biology at UC Riverside.
There is a caveat, however. The review also reports that same-sex behaviors are not the same across species, and that researchers may be calling qualitatively different phenomena by the same name.
"For example, male fruit flies may court other males because they are lacking a gene that enables them to discriminate between the sexes," Bailey said. "But that is very different from male bottlenose dolphins, who engage in same-sex interactions to facilitate group bonding, or female Laysan Albatross that can remain pair-bonded for life and cooperatively rear young."
Published June 16 in the journal Trends in Ecology & Evolution, the review by Bailey and Marlene Zuk, a professor of biology at UCR, also finds that although many studies are performed in the context of understanding the evolutionary origins of same-sex sexual behavior, almost none have considered its evolutionary consequences.
"Same-sex behaviorscourtship, mounting or parentingare traits that may have been shaped by natural selection, a basic mechanism of evolution that occurs over successive generations," Bailey said. "But our review of studies also suggests that these same-sex behaviors might act as selective forces in and of themselves."
A selective force, which is a sudden or gradual stress placed on a population, affects the reproductive success of individuals in the population.
"When we think of selective forces, we tend to think of things like weather, temperature, or geographic features, but we can think of the social circumstances in a population of animals as a selective force, too," Bailey said. "Same-sex behavior radically changes those social circumstances, for example, by removing some individuals from the pool of animals available for mating."
Bailey, who works in Zuk's lab, noted that researchers in the field have made significant strides in the past two and a half decades studying the genetic and neural mechanisms that produce same-sex behaviors in individuals, and the ultimate reasons for their existence in populations.
"But like any other behavior that doesn't lead directly to reproductionsuch as aggression or altruismsame-sex behavior can have evolutionary consequences that are just now beginning to be considered," he said. "For example, male-male copulations in locusts can be costly for the mounted male, and this cost may in turn increase selection pressure for males' tendency to release a chemical called panacetylnitrile, which dissuades other males from mounting them."
The review paper:
Examines work done to test hypotheses about the origins of same-sex behavior in animals.
Provides a framework for categorizing same-sex behavior, for example, is it adaptive, not adaptive, occurs often, infrequently?
Discusses what has been discovered about the genetics of same-sex behavior, especially in the model organism, the fruit fly Drosophila, and in human beings.
Examines connections between human sexual orientation research, and research on non-human animals, and highlights promising avenues of research in non-human systems.
[Home] [Full version] [RSS feed] [Forum]
According to a recent study, almost every kind of animal on  engages in same-sex sexual behavior whether intentional or natural. Lead scientist on the study, Nathan Bailey, says the list includes, among others, , penguins, frogs and .

"It's clear that same-sex sexual behavior extends far beyond the well-known examples that dominate both the scientific and popular literature," said Bailey, a postdoctoral researcher of biology at .

The study was published in today's edition of the journal ''''.

In some cases the animals are not aware that they are engaging in same-sex sexual behaviors. One example are male . According to the study, males in some cases will unintentionally cater to other male flies because they lack a gene which allows them to determine the sexes of other fruit flies.  have also been known to sometimes engage in same-sex sexual behavior as a way to socially bond with other dolphins.

Bailey states that such actions will have an effect on , but that science is only just beginning to research what the effects might be. Bailey also said that natural selection could be playing a role in what animals engage in same-sex sexual behavior.

"Like any other behavior that doesn't lead directly to reproduction — such as aggression or  — same-sex behavior can have evolutionary consequences that are just now beginning to be considered," Bailey said.

He added that "same-sex behaviors — , mounting or parenting — are traits that may have been shaped by natural selection, a basic mechanism of evolution that occurs over successive generations."

Scientists included in the study research on the origins of homosexual behavior in animals, examining whether the behavior is adaptive in an animal's environment, and whether it happens often.