Male Flour Beetle: “Woman! Why are you hooking up with Jeff from the hardware store?… And Bob the Doctor?…and Ted the investment banker?”
Female Flour Beetle: “Sorry, Jerry, but you’re sperm’s just not genetically compatible.”
In the September 23rd issue of Science, researchers across the pond at the University of East Anglia found that inbred populations have a natural increase in female promiscuity to thank for preventing the harmful effects in offspring that come with getting it on with one’s cousin. Females actually take on more mates to screen out sperm from males that aren’t a good fit genetically.
For awhile, scientists have been wrestling with the evolutionary enigma of why some girls are so darn trampy. Although fairly rare in humans (to my knowledge?!), polyandry – where multiple males fertilize a female’s eggs – is commonplace for a wide variety of organisms from chimps to sea urchins. However, in a lot of these situations, things don’t turn out so great for the female. Hence, the enigma.
Using red flour beetles as their model species, the Brits set up inbred and non-inbred mating groups. They found that females who hooked up with just one partner only produced about half as many surviving offspring as those who mated with five males. The Brits double checked for male infertility, but found nothing. So, the only other explanation was that those guys just didn’t have the most “genetically compatible” sperm aka they were too closely related. The scientists then took it a step further and manipulated non-inbred populations to start inbreeding. Sure enough, after about 15 generations, the females started getting frisky and changed their mating patterns. They’re still working on how exactly the females weed out the bad sperm, but…
Moral of the story: Genetic diversity is super important, and a species will go to to great lengths to preserve it. And, don’t hook up with your cousin, even if you’re a beetle.