Sexual system has important implications in evolution and ecology which will affect the levels of genetic variation, the degree of inbreeding, the ability of adaptation to novel environments, as well as the formation of new species (The Tree of Sex Consortium et al., 2014). However, little is known about the evolution of different sexual systems. Sex development can be mainly divided into two processes, sex determination and sex differentiation. Sex determination is the developmental decision that leads the undifferentiated gonad to develop as a testis or ovary, and sex differentiation, which occurs once the gonad has developed and is induced by the products of the gonad to establish the phenotypic sex

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