Male pregnancy has interesting implications for sex roles in mating, Jones explained, because in most species, males compete for access to females, so you usually see the evolution of secondary sex traits in males (for example, a peacocks tail or antlers in deer). But in some species of pipefish, the sex roles are reversed because males become pregnant and there is limited brood pouch space. So females compete for access to available males, and thus secondary sex traits (such as brightly colored ornamentation) evolve in female pipefish instead of males.
From a research standpoint, its interesting because there arent very many species in which there is a sex role reversal, Jones said. It provides a unique opportunity to study sexual selection in this reversed context.
To study the mating behavior of seahorses and pipefish, Jones lab uses molecular markers for forensic maternity analysis to figure out the mother of a males offspring. The lab found that gulf pipefish mate according to the classic polyandry system, where each male receives eggs from a single female per pregnancy, but females can mate with multiple males. Because attractive females can mate multiple times, this system results in very strong competition in sexual selection, and female gulf pipefish have evolved strong secondary sexual traits, Jones said.
Seahorses, however, are monogamous within a breeding season, and each seahorse only mates with one other seahorse. In this system, if there are equal sex ratios, there is not as much competition among females because there are enough mates for everyone, Jones explained. So seahorses have not evolved the strong secondary sexual traits that pipefish have.
|Contact: Keith Randall|
Texas A&M University