Male Guppies' Claws on Genitals Prevent Females from Escaping During Mating

Male guppies use claws to hook the females so that they don't escape during mating, a new study shows.

Guppy is a freshwater fish that belongs to the family, Poeciliidae. The fish are brightly colored- with males having diverse color patterns than females. Guppies are often bred as pets in home aquariums.  

Male guppies are interested in mating with as many females as possible as making sperm is easy and they have limited lifespan, while females live longer and invest more in producing the egg so tend to be choosier about their partners. This leads to sexual tension between male and female guppies as they have different requirements to choose a mate.

For the study, researchers from University of Toronto looked at the claws at the tip of the gonopodium (essentially the penis) of the male guppy.

There are two theories to explain the presence of these claws; one is that they are used to hold the sperm that can be transferred to the female genitalia during mating. Another reason is that the claws hook the female so she can't escape during mating.

"Our results show that the claws are used to increase sperm transfer to females who are resisting matings. This suggests that it has evolved to benefit males at the expense of females, especially when their mating interests differ," said Lucia Kwan, PhD candidate in U of T's Department of Ecology and Evolutionary Biology and lead author of the study.

The researchers surgically declawed a group of guppies and then analyzed the number of sperms that they transferred. They then compared the reproduction success of the declawed fish to that another set of guppies whose genitals weren't mutilated.

"Clawed males transferred up to three times more sperm to unreceptive females compared to declawed males," said Kwan in a news release. "The claw has evolved to benefit the males at the expense of females, and implicates sexual conflict between the sexes in the diversification of the genitalia in this family of fish.

"This provides support that this important selective force is behind an evolutionary pattern that evolutionary biologists have been trying to unravel for over a century," Kwan added.

The study paper," "Sexual conflict and the function of genitalic claws in guppies (Poecilia reticulata)," is published in the journal Biology Letters.