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Scicurious

The good, bad and weird in physiology and neuroscience
Bethany Brookshire

Scicurious

Don’t mount so fast! That bug could be a boy

Study examines same-sex mating behavior in bugs

The red flour beetle is one of the species exhibiting same-sex mating behavior.

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There are many animal species out there that exhibit same-sex mating behavior. This can take the form of courtship behaviors, solicitation, all the way through to mounting and trading off sperm. In some species, it’s clear that some of this behavior is because the animals involved have pair bonded. But what about insects? Many insects mate quickly, a one and done approach, with very little bonding involved beyond what’s needed to protect against other potential suitors. When it comes to bugs, is it intentional same-sex behavior? Or is it all a mistake? Hypotheses are out there, but in the end, we need science.

A new study in the November Behavioral Ecology and Sociobiology wants to answer these questions. The authors did a meta-analysis of papers looking at same-sex sexual activity in male insects and arachnids. They tried to tease out why same-sex sexual behavior might occur in insects. What are the benefits? The potential downsides? And from that, to hypothesize why it might occur.

Some of it, it turns out, could be due to context. A lot of observed same-sex mating behavior in insects is observed, for example, when the males are all housed together, away from the females. Partially because of this (but possibly for other reasons as well), same-sex sexual behavior in insects tends to occur much more frequently in the lab than in the wild. But it’s still often documented in the field.

Why does it happen? Some say that by mating with a “passive” male and transferring sperm, that sperm then gets passed over to the female when the passive male mates. Sneaky. But does it really happen? And if it does, is it effective? So far, it doesn’t appear that it is; less than 0.5% of the offspring resulted from the transfer of sperm when these cases were documented.

Maybe it could be used to get rid of old sperm? Or to decrease risk of predation as the males glom on to each other? Safety in numbers, you know. Maybe there’s a social benefit, or maybe it decreases competition. By mating with other males, the more aggressive bugs could cause damage, or prevent the males from mating with females. Younger males could be using same-sex activity to get “practice” before moving on to the ladies. Finally, it could just be that no potential sex opportunity is worth passing up, and when same-sex sexual behavior happens, it’s a case of mistaken identity. The authors are putting the most weight on the last hypothesis. After all, many bugs can’t be bothered to distinguish between species (or even objects), and if you can’t tell a female from a beer bottle, isn’t a male vs. female question that much harder? It could be that the costs of not mating at all are higher than mating with the wrong sex by mistake.

If it is mistaken identity, as the authors hypothesize, it certainly happens a lot. Why could you get so many cases of false identity? Well, some of it could depend on how the males try to distinguish between the sexes in the first place. What if, for example, some species distinguish males from females by size? Very big or very small males might suddenly find themselves facing some very confused and amorous bugs. What if insects distinguish based on pheromones? That might be easier, but as the article points out, males may end up covered in female pheromones when they mate with a female, resulting in dude smells like a lady. Some younger males could themselves emit female pheromones in some cases. Heck, with a lot of females around, the air might be FILLED with pheromones. You’re a lady! You’re a lady! EVERYONE’S a sexy lady!  

In many observed cases, the males being mated with attempted to fight off the attackers. In others, they may emit pheromones of their own that let the males know that nope, this isn’t what you’re looking for. In some cases, the targeted male just runs away. But it’s hard to tell how often this happens, as no one has ever really studied it.

And this is the problem. The meta-analysis of the papers, talking about all the observed cases, is very interesting…but very few of the hypotheses have been tested. Most of the insect orders in which male same-sex behavior has been documented have at most one or two studies. And of those, most are not focused on same-sex mating behavior; they just list it as a by-product. So it would be interesting to test these hypotheses, and to figure out what is really driving the guy-on-guy bug action. Is it pheromones? Desperation? Safety in numbers? Or something else? Science in the future will have to tell. 

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