Reproductive Costs in Two Sex-Role Reversed Pipefish Species (Syngnathidae)

Abstract

(1) In two species of pipefish (Syngnathidae) the reproductive costs of the two sexes were compared to see how they might influence patterns of sex-role reversal. (2) In Syngnathus typhle, males brood their offspring in a brood pouch, providing them with nutrients and oxygen. Sexes are monomorphic. Males faced reproductive costs in terms of a lower food intake compared with females. Also, males grew more slowly than females, which yields a cost to future reproduction, as larger males could brood more offspring. No sexual difference in predation risk was found. The over-winter survival of males was probably lowered because intestinal fat deposition was delayed as a result of their reproductive efforts. (3) In Nerophis ophidion, males brood their offspring attached to their ventral body side, and provide them with nutrients and oxygen. Sexes are dimorphic, females being larger and brighter in colour. Males suffered an increased predation risk when brooding. No indications of energetic costs were found, e.g. through a lowered food intake or a slower growth rate. (4) Reproductive costs differed in the two species, probably reflecting differences in brood care. However, in both species the limiting sex, males, faced higher reproductive costs than females, as would be expected in sex-role reversed animals.