traumatic insemination? ooh that sounds painful!

Bedbugs. One of the critters that I’d prefer not to encounter on my travels. They come out at night and bite sleeping humans (& other animals), retreating during the day to their dark hideaways, often in cracks in furniture, walls, or floors. This sounds very insanitary but the species that bites humans, Cimex lectularius, isn’t generally regarded as a disease vector, and while a review published in 1963 found that bed bugs can carry a range of pathogens, the author also concluded that there was no scientific evidence of actual transmission of disease. At least one recent research study found that Rickettsia could survive in the insects’ blood for several days after infection, but again noted no evidence that the pathogen was spread in the bugs’ bites.

Now, I know that a bug’s gotta do what a bug’s gotta do. But even when it comes to their love lives, bed bugs are just not that, well, nice. For mating in the African bat bug (a relative of C.lectularius) sounds more like open warfare than a tender meeting of the sexes.

In this, and in other Cimex species (including lectularius), male bugs don’t mess around. Rather than find the female’s genitalia & follow a more normal route, the male simply stabs his penis into his mate’s abdomen. Ouch! Traumatic insemination, indeed. His sperm are injected into her blood-filled body cavity (insects have an open circulatory system) and make their way thence to her ovaries. Not only is the female physically damaged by this act, but it must also open the door to infection by pathogens. It turns out that males are also susceptible to damage as they are not too fussy about who they mate with, and at times another male ‘will do’.

The risk of harm is not trivial, and so individuals with any trait that might minimise the harm is going to be at a selective advantage (& if that trait has a heritable component, the underlying alleles will spread through the population’s gene pool). The result is the evolution of ‘paragenitals’ in both males and females: structures described as ‘extra genital funnel[s]’ (Dolgin, 2007) that are easy to access and increase the odds that matings will be in that spot rather than randomly all over the abdomen. What’s more, the male’s penis enters a cavity lined with immune cells (like all animals, insects have an innate immune system), which reduces the odds that the mating partner will pick up an infection. 

There is, of course, a disadvantage to a male bug in looking like a female – more males may start to hit on him. Consequently males’ paragenitals differ from females’ in that they are more open (their funnel is a different shape). But the story doesn’t stop there. It turns out that at least some female bat bugs’ paragenitals look more like those of the males – and that this deception works: counting the scars on their abdomens, & comparing the results with the scores for more girly girls, showed that male-like females had suffered fewer of those random mating stabbings.

I shall let the reporter at Evolution (on Facebook, where I first spotted this story) have the last word:

If you’re having trouble envisioning this cross-dressing insanity, picture this – the males are dressed like girls, and the girls dressed like guys who are dressed like girls, and everyone’s doing this to avoid sex.

(Avoid it as much as possible. But not completely – for that route would lead to the oblivion of extinction.)

E.Dolgin (2007) Bug sexual warfare drives gender bender: African bat bugs have two types of female genitalia Nature (published online 20 September 2007) doi: 10.1038/news070917-7



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