Sex ratio does not influence sex change despite its effect on reproductive success

The sex ratio of adults in a population affects the reproductive value of being either a male or female and thus may be a cue for sex change in sequentially hermaphroditic species. We examined the effect of the sex ratio on reproduction and sex change of the reef fish, Lythrypnus dalli, and predicted that the sex ratio would influence the reproductive success for a given body size and thus the probability of sex change. We varied adult sex ratios on artificial patch reefs, monitored egg production over 20 days, and examined rates of sex change. We found no evidence that sex ratio influenced the size at which individuals change sex despite its influence on relative reproductive success. The sex ratio influenced the average reproductive success of males but not females, with males having both a higher probability of mating and higher per capita reproductive success on strongly female-biased reefs. However, females did not capitalize by changing sex to male more frequently. Female per capita reproductive success did not vary with changes in the sex ratio or female density, suggesting that females were not limited by male or resource availability. Male to female sex change was rare, suggesting that, although physiologically possible, this behavior may be uncommon in natural populations. Overall, our results indicate that the sex ratio may not be a good predictor of the reproductive value of sex change for a given individual and that body size alone may provide sufficient information regarding reproductive potential for a given sex.