Meeting Abstract

63.3  Wednesday, Jan. 6  Mechanism of an inducible morphological defense: active physiological response or behavioral by-product? BOURDEAU, PE; Michigan State University bourdea7@msu.edu

Many organisms have evolved inducible defenses in response to spatial and temporal variability in the risk of predation. These defenses are assumed to be costly, but few studies have investigated the mechanisms and of these adaptive responses, which can often elucidate associated costs. I examined the proximate cause of a known inducible defense; crab-induced shell thickening in the marine snail Nucella lamellosa. Results indicate that although crabs (Cancer productus) induce thicker shells, the response is a passive consequence of reduced feeding and somatic growth rather than an active physiological response to predation risk. Physical tests indicate that the shells of crab-induced snails are stronger, but the increase in strength is no different than that of snails with limited access to food. Increased shell strength is also attributable to an increase in the energetically inexpensive microstructural layer rather than to material property changes in the shell. This mechanism suggests that crab-induced shell defenses may be neither energetically nor developmentally costly. Positive correlations between behavioral responses and morphological defenses may explain the commonly observed associations between growth reduction and defense production in other systems and could have important implications for the evolutionary potential of these plastic traits.