Mate quality influences multiple maternity in the sex-role-reversed pipefish Syngnathus typhle

In the pipefish Syngnathus typhle, pregnant males provide all parental care . Females are able to produce more eggs than males can brood, and consequen tly females compete more intensely for males than do males, a phenomenon de fined as sex-role reversal. As the genetic mating system influences the ope ration of sexual selection, we investigate variation in one phenotypic comp onent of male quality, female body size, as a possible proximate influence on mating system variation in S. typhle. Breeding trials were employed, eac h consisting of a single receptive male with four adult females. In each re plicate, a focal male was paired either with a set of small or with a set o f large females. Males were allowed to mate freely, and after several weeks of brood development, maternity of the progeny was resolved using three mi crosatellite loci. Males with access either to small or to large females su ccessfully mated with a mean of 2.1 or 1.3 females, respectively, a signifi cant difference. Results indicate that variation in female size can affect the mating system and thereby influence sexual selection in pipefish. Thus, the high rate of multiple mating by S. typhle males in the wild may be exp lained in part by the extensive size variation in naturally occurring, sexu ally mature females.