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| Review Finds Same-sex Behavior In Nearly All Animals |
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| Living - Relationships | |||
| TS-Si News Service | |||
| Monday, 22 June 2009 21:00 | |||
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Riverside, CA, USA. 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. A pair of evolutionary biologists found that the majority of existing studies focus on why same-sex behavior in animals may exist, but the studies do not fully examine its consequences. 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. "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.
London, United Kingdom. New findings argue for the persistence of sex-linked chromosomes, such as the male Y  chromosome, refuting theories that the Y is doomed to extinction.
The results confirm that although these chromosom...
The review by Marlene Zuk, a UCR professor of biology, and Nathan Bailey (who works in Zuk's lab) appears in Trends in Ecology & Evolution.They found that many studies are performed in the context of understanding the evolutionary origins of same-sex sexual behavior, but almost none consider its evolutionary consequences. "Same-sex behaviors — courtship, mounting or parenting — are traits that may have been shaped by natural selection, a basic mechanism of "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 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 reproduction — such as aggression or altruism — same-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:
The reviewers expected the research papers they read for their article would give them a better understanding of the degree to which same-sex behaviors are heritable in animals. "How important are genes to the expression of these behaviors, compared to environmental factors?" Bailey said. "This is still unknown. Knowing this information would help us better understand how the behaviors evolve, and how they affect the evolution of other traits. It could also help us understand whether they are something that all individuals of a species are capable of, but only some actually express." Bailey recommends that fellow evolutionary biologists studying same-sex behavior in animals adopt some of the research approaches that have been successful in human studies. "We have estimates, for example, of the heritability of sexual orientation in humans, but none that I know of in other animals," he said. "Scientists have also targeted locations on the human genome that may contribute to sexual orientation, but aside from the fruit fly, we have no such detailed knowledge of the genetic architecture of same-sex behavior in other animals." In the next phase of their research, Bailey and Zuk plan to begin experimentally addressing some of the many issues raised in their review. Bailey says they want to "... get at this question: what are the evolutionary consequences of these behaviors? Are they important in the evolution of mating behavior, or do they just add extra 'background noise'? We are pursuing work on the Laysan Albatross, in which females form same-sex pairs and rear young together. Same-sex behavior in this species may not be aberrant, but instead can arise as an alternative reproductive strategy." FundingThe UCR Academic Senate funded the one-year study.
CitationSame-sex sexual behavior and evolution. Nathan W. Bailey and Marlene Zuk. Trends in Ecology & Evolution. (in press)
Abstract Same-sex sexual behavior has been extensively documented in non-human animals. Here we review the contexts in which it has been studied, focusing on case studies that have tested both adaptive and non-adaptive explanations for the persistence of same-sex sexual behavior. Researchers have begun to make headway unraveling possible evolutionary origins of these behaviors and reasons for their maintenance in populations, and we advocate expanding these approaches to examine their role as agents of evolutionary change. Future research employing theoretical, comparative and experimental approaches could provide a greater understanding not only of how selection might have driven the evolution of same-sex sexual behaviors but also ways in which such behaviors act as selective forces that shape social, morphological and behavioral evolution.
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