Females benefit when males mount other males.
When a male seed beetle gets in the mood, he’ll normally seek out a female to mount. But sometimes, it’s another male that finds himself on the receiving end.
Why some animals engage in same-sex sexual behavior (SSB) has long puzzled evolutionary biologists since it does not carry the obvious benefits of heterosexual courtship, which can lead to mating and production of offspring.
Researchers at Uppsala University in Sweden have discovered that, when male beetles were selectively bred to display increased SSB, their sisters laid more eggs and had more offspring than they had previously.
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Because males and females share most of their genes, SSB was hypothesized to occur in one sex because its underlying genes carry benefits when expressed in the other.
The benefits would have to be large to make up for the potential downsides of SSB, which include the risk that the male’s spiky penis will get trapped in the wing casing of the other male, possibly leading to death of both partners. SSB is also a massive waste of time and energy for males, given that it doesn’t up their odds of siring offspring.
The findings, published in the journal BMC Evolutionary Biology, support the idea that SSB may persist in males despite being so detrimental because the genes underlying the behavior confer benefits to females that are favored by natural selection — a genetic tug of war between the sexes.
There aren’t many clear examples in animals of these tugs of war operating between males and females, likely because it’s hard to know for certain that a particular trait provides absolutely no benefits for a given sex. Nonetheless, many species are known to engage in SSB with no obvious benefits, and this research might offer a clue as to why it persists throughout the animal kingdom.
“The genetic mechanism we illustrate could equally well apply to other animals,” study lead author David Berger told The Science Explorer in an email.
Nevertheless, Berger cautions against looking to these results to explain the underpinnings of homosexuality in humans. “[T]he details of our findings — the species being a very different creature and the traits we study being very different and irrelevant to human sexuality — are not possible to extrapolate to humans,” he wrote.
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