Consequences of Male Brood Care; Weight and Number of Newborn in a Sex-Role Reversed Pipefish

Abstract

1. In the pipefish Syngnathus typhle sex roles are reversed, as females compete for access to males. In this species males provide all brood care (i.e. are 'pregnant') and female reproductive rate exceeds the reproductive rate of males. Consequently females are limited by access to mates and male reproductive success is limited by male brooding ability and/or mate quality. Thus, phenomena like brood reduction and a trade-off between number and weight of newborn may be expected in males. 2. In this paper I demonstrate the following in males of S. typhle: (a) the initial weight of the egg (received from the female) positively influenced the weight of newborn; (b) in the male's brood pouch, number of newborn frequently is less than number of eggs initially received (brood reduction), and the extent of this decrease in brood size positively influenced the weight of newborn; (c) a trade-off between number and weight of newborn was demonstrated in males from field samples and in large experimental males (independent of brood reduction), but not in small males that presumably allocated resources to several other demands (condition, growth, etc.); (d) paternal length, per se, did not affect the weight of newborn. 3. The results indicate that in S. typhle, male reproductive success is limited by their own brooding ability and influenced by the egg size received (indirectly quality of mate), which may be expected in a situation of sex-role reversal.