Morphological asymmetry of the abdomen and behavioral laterality in atyid shrimps.

Morphological asymmetry and behavioral laterality in vertebrate species have been intensively studied in recent years, while comparable invertebrate studies are rare. Here we demonstrate asymmetry in the curvature of the abdomen and laterality in evasive responses for two atyid shrimps, Limnocaridina latipes and Neocaridina denticulata. The frequency distributions of the angle of the abdominal curvature in both species were discretely bimodal, suggesting that the two populations are composed of both left- and right-type individuals. In N. denticulata, behavioral analysis using high-speed filming illustrated that the escape direction for each individual, evoked by a sudden non-lateralized stimulus, was correlated with its abdominal curvature: left- (right-) type shrimp jumped back-leftward (-rightward) significantly more than often. A crossing experiment with N. denticulata indicated that the trait frequency in the F1 generation from two left-type parents differed significantly from that of the F1 generation from two right-type parents, and that the trait frequency for the F1 generation from parents of different laterality types did not deviate from random. That is, offspring laterality type is affected by the lateralities of the parents, indicating that abdominal dimorphism in shrimp is genetically derived. These results suggest that shrimp have an innate laterality that controls their escape direction, which in turn may affect prey-predator interactions in the aquatic community.