Sex differences in oxygen consumption in Japanese medaka (Oryzias latipes)

Abstract

One of the defining characteristics in sexual dimorphism is that there are morphological differences between the sexes. Sexual selection favors traits that are advantageous for reproduction, usually acting on males due to their higher variability in reproductive success, often resulting in sexual dimorphism. In Japanese medaka (<i>Oryzias latipes</i>), sexual dimorphism can be observed in the larger size of male anal fins, which functions in reproduction, and larger body size in females which results in increased fecundity. Large body size in males is attributed to greater mating success compared to smaller body size males. To assess whether or not dimorphism is related to physiological differences between males and females, I examined the rates of oxygen consumption between the sexes to determine whether higher weight contributed to differing oxygen consumption. Individual medaka were assessed for oxygen consumption over a 30-minute time period. Weight was moderately positively correlated with increasing oxygen consumption in males, and there was no correlation for females. Males had a higher average weight than females (0.168g vs. 0.159g). There were differing rates of oxygen consumption between the sexes not influenced by weight during the trials, suggesting that there may be additional physiological differences which are responsible for the difference in oxygen consumption between the sexes.