Sex-role reversal revisited: choosy females and ornamented, competitive males in a pipefish

In the pipefish Syngnathus typhle sex roles are reversed, that is, females compete more intensely than males over mates. However, competition over mates among individuals of one sex does not necessarily prevent members of that same sex from being choosy, and choosiness in the other sex does not prevent competition within it. In an experiment we allowed a female pipefish to choose freely between two males, after which we released the males and let the three interact. Comparisons with earlier results show that both sexes courted partners and competed with consexuals. However, females courted more often than did males, and courtship was more frequent in treatments involving large individuals than in treatments with small individuals. Males competed among themselves for access to mates but for a shorter duration than females in the same situation. Males displayed an ornament towards females but not to males during mating competition. Females, however, used their ornament in both contexts. Females did not always mate with the male of their previously made choice, which we interpret as females being constrained by male-male competition, male motivation to mate, or both. Thus, in this sex-role reversed species, mate choice in the more competitive sex may be circumvented and even overruled by mate competition and mating willingness in the least competitive sex. Hence, sex roles should not be considered as sexes being either choosy or competitive but rather that males and females may exhibit different combinations of choice and competition.