Meeting Abstract

81.3  Monday, Jan. 6 10:45  Effects of predator odor on photobehavior, visual sensitivity, and morphology of crab larvae CHARPENTIER, C.L.*; COHEN, J.H.; University of Delaware; University of Delaware charpecl@udel.edu

Many zooplankton exhibit specialized behavioral and morphological predator defense strategies that are induced by predator detection. For example, exposure to predator odor enhances photobehavior in the larval crab Rhithropanopeus harrisii, likely exaggerating light-driven vertical migration patterns that are thought to aid in predator avoidance. Although predator-induced behavioral changes have been observed, we lack a physiological mechanism to explain these changes, and predator-induced morphological defenses have not been examined in crab larvae. Following short (1 h) exposures to either odor-free seawater or odor from the zooplanktivorous fish Fundulus heteroclitus, behavioral assays were conducted on two species of crab larvae (R. harrisii, Hemigrapsus sanguineus) to confirm that predator odor enhances photobehavior, which it did. To test the hypothesis that altered photobehavior was mediated by increased visual sensitivity at the primary photoreceptor level, response-irradiance (V-LogI) curves were generated from extracellular electroretinogram recordings. In addition, external morphology at each larval stage of both species was compared between individuals reared in odor-free or predator-odor containing seawater. Exposure to predator odor shifted V-LogI curves to lower irradiances, suggesting that predator odor induces behavioral changes by increasing visual sensitivity at the retinal cell level. Predator odor also affected morphology, namely body size and length of anteriorly protruding spines. These data suggest that chemosensory inputs such as predator odor induce behavioral and morphological predator-avoidance strategies in R. harrisii and H. sanguineus and that altered photobehavior is mediated at the photoreceptor level.