It's in the Genes: Why Same-Sex Sexual Behavior is Pervasive in Animals

The same-sex sexual behavior (SSB) in the animal kingdom has long baffled the scientific community. Since it is not done for the purpose of directly creating offspring, why would the animals do it?

Researchers at the Department of Ecology and Genetics at Uppsala University reveal the reason behind this enigmatic behavior. SSB could be explained by genes that are favored by natural selection when expressed in the opposite sex, the study published in the open access journal BMC Evolutionary Biology said.

Previous explanations of the behavior include misidentification of their own sex or over-dominance, but in this particular study, researchers hypothesized that, SSB may occur in one sex because it has an evolutionary advantage meaning underlying genes carry benefits when expressed in the other.

To prove hypothesis, they compared the morbidity and reproductive success of beetles that display increased SSB and those that perform less SSB.

They found out that those with increased SSB had increased reproductive performance. Specifically, male who engage in frequent SSB have increased fertility rates when they mate with a female beetle. They also showed changes in traits such as mobility and sex recognition after selective breeding on SSB, providing verification of genetic links between SSB and these traits across the sexes, according to the researchers.

"We noted that males that had been bred for increased same-sex mounting behavior were less discriminating when given a choice between courting a male or a female in later tests, while their sisters laid more eggs and produced more offspring than before," David Berger, Assistant Professor at the Department of Ecology and Genetics at Uppsala University and one of the researchers taking part in the study said in a statement.

Researchers claim that these findings may just be applicable to all animal species.

"Our study provides experimental support for the hypothesis that widespread pleiotropy generates pervasive intralocus sexual conflict governing the expression of SSBs, suggesting that SSB in one sex can occur due to the expression of genes that carry benefits in the other sex," the study concluded.