||A male-biased sex ratio was observed in the sea urchins (Tripneustes gratilla, Linnaeus) around Taiwan between 2010 and 2013. In Kenting, south Taiwan, more biased sex ratios were found among larger individuals. Here, we tested the hypotheses of predators, genetic,and sampling biase. We discovered that sex ratio would vary with season, this falsifies the hypothesis of genetics. The external shapes, as compared by height-diameter ratios, and the masking behavior, carrying objects on their aboral surface, were not different between males and females. |
No biase in sex ratio was found in an artificial culture facility whereas field collection indicated a male-biased phenomenon in Penghu in Jul 21 2013. All these evidence are compatible only with the predator hypothesis in which selective predators preferentially feed on females. Based on change of sex ratios, we estimate that the lowest mortality rate was 34% per 1.7 months at Penghu, and was 32% per 1.3 months at Houbihu during the spawning season.