Sexual ratio in populations of Sparisoma radians and Sparisoma atomarium at Los Roques Archipelago, Venezuela: An evolutionary approach

Abstract

A comparative study of two populations of Sparisoma radians and one population of Sparisoma atomarium indicates significant differences in the overall and size-specific adult sex ratio, as well as in the width of the critical size class for sex change of these hermaphrodite marine fish species. Sparisoma atomarium shows an overall sex ratio more biased to females and a rather sharp change in size-specific sex ratio than S. radians, revealing a narrower critical size class for sex change. The differences observed between species agree with that reported in another study, which outlines an evolutionary explanation based on the different mating systems of these species. Significant differences were detected in the form and central localization of size distribution between the two samples of S. radians, accompanied with a displacement in the respective size class for sex change and the constancy in overall sex ratio. This result, in addition to the condition of sex ratio biased to females in the three populations, agrees with predictions of evolutionary models of sequential hermaphroditism.