Gonopodium:
Mating between mosquito fish – a relative of the guppy – is far from romantic. The male makes no effort to court partners. Instead, he sneaks up and attempts to copulate by force up to 1000 times a day – and females try to avoid the harassment. Males use a modified anal fin, the gonopodium, to deliver sperm into the female.
Séverine Buechel at Stockholm University in Sweden and colleagues bred males to have longer gonopodia, and found that this led to bigger-brained females (Proceedings of the Royal Society B, doi.org/bvmv).
From “Longer ‘penis’ drives evolution of bigger brains in female fish,” NewScientist (17 December 2016).
