Potential reproductive rate of a sex-role reversed pipefish over several bouts of mating

The potential reproductive rate (PRR, the rate at which each sex could reproduce if given unlimited mates) has proven to be a useful tool in predicting the direction and strength of sexual selection. We conducted a 2-month study of the PRR in the polyandrous gulf pipefish, Syngnathus scovelli, a year-round breeder. In this sex-role reversed species, the female transfers eggs to a male's brood pouch during mating and thus renders him unavailable to mate for 2 weeks. We predicted females would have a higher PRR than males and that the rates in both sexes would change over successive breeding bouts in relationship to previous reproductive output. Females did have a higher overall PRR than males for the entire study period. However, PRR was not constant across individual breeding bouts. For each sex, the PRRs from the first and third bouts of mating were significantly higher than the PRR of second mating bout. Our results are consistent with individuals making trade-offs between current and future reproductive investment. We also discuss how ovarian morphology may contribute to elevated female PRR in this species. To our knowledge, this is the first study of PRR in a North American pipefish.