A female butterfly is sizing up two males. She has a choice between two butterfly beaus. How does she decide?
It turns out that if one of those suitors is inbred, the female can sniff him out.
A new study exposed female butterflies to both inbred and outbred males. Some of the females had their antennae painted with nail polish, so they couldn’t detect pheromones from the males. The others had normal antennae. What the researchers found was that lady butterflies who could sense pheromones avoided inbred males, while those who couldn’t mated with both equally.
For female butterflies, avoiding inbred males is a big deal. The University of Cambridge explains:
For the butterfly Bicyclus anynana, it is critical that the female avoids breeding with an inbred male as some 50 per cent of the latter are completely sterile. As a result, if a female mates with a sterile inbred male none of her eggs will hatch, and she will therefore produce no offspring.
So it’s really important for females to avoid wasting their energy on offspring that are sterile. The researchers also found that inbred males produce less pheromones. That wasn’t surprising to researchers. What was surprising was how much females depended on those pheromones. Researcher Erik van Bergen explained to Science Omega:
Not entirely, because we already knew that sex pheromones are extremely important for mate choice decisions. We also knew that traits used by males to attract the opposite sex are often affected by inbreeding. What did surprise me is that we were able to restore the mating success of inbred males completely by blocking female perception. So apparently these sex pheromones are the only cues used by the females to detect inbred males. Their general condition, which was also worse, played no discernible role in reducing the mating success of inbred males.
In humans, however, detecting inbreeding isn’t quite as simple.
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