Sexual Systems in Shrimps (Infraorder Caridea Dana, 1852), with Special Reference to the Historical Origin and Adaptive Value of Protandric Simultaneous Hermaphroditism

Abstract

In this chapter, the diversity of sexual systems in the infraorder Caridea is summarized. Caridean shrimps exhibit six different sexual systems: gonochorism (separate sexes), strict protandry, partial protandry with primary females, partial protandry with primary males, partial protandry with primary males and primary females, and protandric simultaneous hermaphroditism. Within monophyletic clades belonging to the species-rich and ecologically dissimilar order Decapoda, gender expression is the most diverse in caridean shrimps. Additional studies on the life history and sexual system of caridean shrimps coupled with improvements on our understanding of the internal phylogenetic relationships within this species-rich clade are needed for a formal testing of transition asymmetries in the group. The historical origin of protandric simultaneous hermaphroditism, a sexual system that represents the “pinnacle” of evolution with respect to gender expression in the Caridea, remains to be fully understood. The conditions that maintain protandric simultaneous hermaphroditism include sex-dependent time commitments and sex-dependent energetic costs. The role of sexual selection in explaining the adaptive value of protandric simultaneous hermaphroditism needs to be addressed. Caridean shrimps represent excellent model systems to continue improving our understanding about the mechanisms explaining the diversity of gender expression patterns in nature.