Sex-specific growth effects in protogynous hermaphrodites

We demonstrate sex-specific decoupling of otolith growth and somatic growth in two species of protogynous parrotfishes, Scarus frenatus and Chlorurus sordidus. Otoliths of both species increased in size consistently through life, even though somatic growth rate decreased with age (age effect). Furthermore, in S. frenatus, otoliths from terminal males were smaller than otoliths from females, despite males being larger than females of the same age. This demonstrates the presence of a sex-specific growth effect, where otoliths of fast-growing individuals (males) are smaller than otoliths of slow-growing individuals (females). The sex-specific growth effect for S. frenatus was most pronounced during the early life history, which suggests that only the fastest-growing females change sex to male. A sex-specific growth effect was also evident in C. sordidus, although it was not statistically significant because of greater variation in the otolith size of terminal males of this species. Our results demonstrate that the relationship between otolith and somatic growth can vary dramatically between the sexes. This will make it difficult to back-calculate size at age in protogynous species, or to conduct sex-specific back-calculations in gonochoristic species, unless the precise relationship between otolith and somatic growth is known for each sex