Planet Earth

The dark side of guppy sex (hint: it involves penis claws).

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Photo: flickr/Mihnea Stanciu

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As if the duck-rape genitalia arms race and traumatic sex in bed bugs weren’t enough, the research presented in this paper now informs us that male guppies have special penis claws that help them rape females. Guppies are extremely popular aquarium fish that give birth (rather than lay eggs) and have been used for much behavioral research, including on breeding behaviors. Males have a modified anal fin, the gonopodium, that is similar in function to a penis. When breeding, the male approaches and thrusts his gonopodium into a female, ejecting one or more balls of sperm. (If you want to see some amateur guppy porn, there are a number of YouTube videos available, like this one.) Male guppies also have claw-like appendages on their gonopodia. When the scientists removed these “gonopodial claws”, the males weren’t able to transfer as much sperm when mating with unwilling females, but were just fine at mating with willing females. 

Sexual conflict and the function of genitalic claws in guppies (Poecilia reticulata).

“Poeciliid fish, freshwater fish with internal fertilization, are known for the diversity of structures on the male intromittent organ, the gonopodium. Prominent among these, in some species, is a pair of claws at its tip. We conducted a manipulative study of these claws in the guppy, Poecilia reticulata, to determine if these aid in transferring sperm to resistant females. We compared the sperm transfer rates of clawed versus surgically declawed males attempting to mate with either receptive or unreceptive (i.e. resistant) females. Our analyses demonstrate that the gonopodial claws function to increase sperm transfer to unreceptive females during uncooperative matings but not during receptive matings. Up to threefold more sperm were transferred to unreceptive females by clawed than declawed males. These data suggest that the claw is a sexually antagonistic trait, functioning to aid in transferring sperm to resistant females, and implicate sexual conflict as a selective force in the diversification of the gonopodium in the Poeciliidae.”

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