You’ve got to feel sorry for the female seed beetle. Whenever she mates with a male, she has to contend with his spiked, nightmarish penis (remember this picture?). And despite the damage that it inflicts, one liaison just isn’t enough; female seed beetles typically mate with many males before they lay their eggs. Surely, she must benefit in some way?
The most likely idea is that she somehow ensures that her eggs are fertilised by sperm from males with the “best” genes – those that either make for particularly fit and healthy young, or that are a compatible match for the female’s own genes. Perhaps these sperm outrace their weaker peers, or maybe the female has a way of selectively letting through the best quality sperm. It would be a reasonable explanation were it actually true. Sadly, reality isn’t that kind to the female seed beetle.
Trine Bilde from the University of Uppsala has found that after females mate with two different males, it’s actually the sperm from the lower-quality specimen that fertilises most of her eggs. Even though the paragon’s sperm would sire more successful offspring, it’s the loser who ends up fathering most of her progeny.