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When the flashy colours and fancy dancing don’t impress her, male guppies—tropical fish common in fish tanks—use claws on their penises to hang on to resistant females.
Evolutionary biologist Lucia Kwan and her collaborators at the University of Toronto, Canada cut the claws off some males, while leaving others intact, to see how this affected their mating success. Their findings, published in Biology Letters this week, show that the claws help males transfer sperm to females when they are playing hard to get. Along with the corkscrew penis of ducks and the spiky penis of seed beetles, these penis claws have likley evolved as a result of differing mating interests between the sexes.