Researchers claim that homosexuality in insects and spiders is most likely usually a case of “mistaken identity”.
Many species of insects and spiders engage in homosexual behaviour, like courting, mounting, and trying to mate with members of the same sex.
But it is unclear what role evolution plays in this curious situation. Like heterosexual behaviour, it takes time and energy and can be dangerous – and it lacks the potential payoff of procreation.
Now Dr. Inon Scharf of Tel Aviv University’s Department of Zoology and Dr. Oliver Martin of ETH Zurich have claimed that homosexual behaviour in bugs is probably accidental, in most cases.
In the rush to produce offspring, bugs do not take much time to inspect their mates’ gender, potentially leading to same-sex mating, say the scientists.
“Insects and spiders mate quick and dirty,” Dr. Scharf commented. “The cost of taking the time to identify the gender of mates or the cost of hesitation appears to be greater than the cost of making some mistakes.”
In birds and mammals, homosexual behaviour has been shown to have evolutionary benefits. It provides “practice” for young adults and maintains alliances within groups.
Scientists have recently tried to find explanations for similar behaviour in insects, suggesting it could serve to prepare for heterosexual courtship, dispose of old sperm, discourage predators, and distract competitors.
But in reviewing research on some 110 species of male insects and spiders, the researchers found that the available evidence weakly supports such adaptive theories. In general there is no clear benefit to homosexual behaviour in insects. The costs, on the other hand, can be considerable.
And yet, in some species, up to 85 percent of males engage in homosexual behaviour. The researchers say this is not because bugs directly benefit from the behaviour, but because they mistake other males for females.
Almost 80 percent of the cases of homosexual behaviour the researchers appeared to be the result of misidentification or belated identification of gender.
In some cases, males carry around the scents of females they have just mated with, sending confusing signals to other males. In other cases, males and females look so similar to one another that males cannot tell if potential mates are female until after they have mounted them.
They also noted many insect species that exhibit homosexual behavior also mate with related species or inanimate objects, like beer bottles — indicating a general tendency toward misidentification.
It is also possible that sexual enthusiasm in bugs is related to other evolutionarily beneficial traits, the researchers say.
“Homosexual behaviour may be genomically linked to being more active, a better forager, or a better competitor,” says Dr. Schart. “So even though misidentifying mates isn’t a desirable trait, it’s part of a package of traits that leaves the insect better adapted overall.”
The study was published in Behavioral Ecology and Sociobiology.