Experimental evidence of a sex reversal process in the shrimp Hippolyte inermis

Hippolyte inermis Leach 1815 is a shrimp which forms stable populations in seagrass meadows of the Mediterranean Sea and along the Atlantic coast of Spain. Investigations from the last century have demonstrated specimens experiencing a male stage prior to switching to females (i.e., protandric sex reversal). Further studies have demonstrated that not all females are derived from sex reversal: young females apparently deriving from direct differentiation are present in natural populations. In recent years some authors have claimed that the species is simply gonochoristic, mainly based on the absence of ovotestis development. In order to establish if the species is a peculiar hermaphrodite or a simple gonochoristic, H. inermis postlarvae were individually cultured in Petri dishes in a semi-closed system. Their exuviae were regularly collected, fixed and stained, to monitor the sex and the size of each individual over time. In addition, histological sections were examined and we observed an individual who lost its appendix masculine and developed an active ovary. In contrast, specimens that retained their appendices masculinae exhibited a male reproductive system. Fourteen such individuals who lost their appendices masculinae were observed throughout the experiment, suggesting a mechanism of sex reversal in decapod crustaceans in which an ovotestis may be absent during the transition to the opposite sex.