Female pipefish face toughest odds

In the world of pipefish, which are cousins of sea horses, sexual selection may reverse in the most dramatic way yet recorded.

Biologists have most often talked about sexual selection as a force driving males to evolve lures for females. Now, Adam G. Jones from Oregon State University in Corvallis says the Gulf pipefish, Sygnatha scovelli, breaks the pattern.

Like other members of the seahorse family, a female pipefish mates by transferring eggs to a male. He fertilizes the eggs and then carries them to term in a brood pouch.

Females have flashy physiology, such as colorful stripes and deep ridges on their bellies, but males don’t. This and the males’ pregnancy inspired theorists to predict a looking glass world of females battling for male favor.

Jones and his colleagues tested the idea using genetic analyses. The researchers collected 27 female and 34 male pipefish from a patch of sea grass in Florida’s intracoastal waterway. Twenty-seven males were pregnant, and the researchers used genetic data from the moms, dads, and babies to identify the heritage of 14 of the broods.

According to several indices, the females faced more sexual selection than the males did, Jones and his colleagues contend in the Dec. 22 issue of Proceedings of the Royal Society of London B. For example, the researchers calculated variations in the success of individual pipefish to secure mates. Among females, the range of success was roughly seven times greater than that among males. During a male’s pregnancy, the female may mate with several other males.