Allometric differences between two phenotypes of the amphidromous shrimp Xiphocaris elongata

Abstract

The amphidromous shrimp Xiphocaris elongata (Guerin-Meneville, 1855) has a long rostrum in the presence of predatory fishes and a short rostrum above steep waterfalls where predatory fishes are absent, i.e., typically above waterfalls. Prior experiments showed that elongated rostrum in X. elongata is induced by chemical signals from the predatory fish Agonostomus monticola . We tested the hypothesis that in addition to rostrum length there are other morphometric differences between long-rostrum (LR) and short-rostrum (SR) X. elongata . We measured the post-orbital carapace length and pleon length of LR and SR shrimp and weighed both shrimp morphs. LR shrimp have significantly longer and heavier pleons than the SR shrimp. These allometric differences may affect the behavior of X. elongata shrimp in ways that, in turn, affect their interactions with predators and the environment. Our study demonstrates the importance of taking pleon measurements when studying crustaceans given that these measurements have been mostly overlooked, and may provide insight of environmental influences on crustacean morphology and behavior. This research provides data of the differences between prey phenotypes, which may alter their life-histories and interactions with the environment.