Hermaphroditism and gonochorism. a new hypothesis on the evolution of sexuality in crustacea

Most crustaceans are gonochoristic but hermaphroditism occurs in primitive classes as well as in different orders of higher Crustacea. Though studies have been carried out in plants and animals on the advantages of these two types of sexuality, it is not known how hermaphroditism can change into gonochorism and vice versa. The new hypothesis we report here is based on recent results on biased sex ratio in Crustacea. We suggest that ancestral sexuality was a simultaneous hermaphroditism as it exists still today in primitive groups. Gonochorism may have appeared following integration in the host genome of a parasitic xenogenous DNA inhibiting expression of ‘male genes’. Female sex would be anterior to male sex, and male heterogamety can be seen as a by-product of an intragenomic conflict in a species with an ancestral female heterogamety. Sequential hermaphroditism in higher Crustacea would be a secondary hermaphroditism resulting from other genetic conflicts between host genes and repressing heterochromosomic genes (parasitic DNA from xenogenous origin?)