Meeting Abstract

95.2  Wednesday, Jan. 7  Stuck between a rock crab and a hard place: phenotypic responses to multiple predators in a marine snail. BOURDEAU, Paul/E; Stony Brook University bourdeau@life.bio.sunysb.edu

I examined the single and combined effect of chemical cues from crabs and seastars, two predators with contrasting attack modes, on the shell morphology of the marine snail Nucella lamellosa. Snails were subjected to three nonlethal predator treatments: seastar (Pisaster ochraceus), crab (Cancer productus), a combination of seastar and crab, and a no predator control. Shell shape, shell thickness and resistance to shell entry and shell breaking were quantified. I also analyzed whether shell shape or thickness plasticity was actively modulated in response to predators or an indirect effect of reduced feeding and growth. Predator-specific responses reflected the foraging mode of the predator that induced them. Chemical cues from the seastars induced elongate shells with tall spires, which facilitated soft tissue withdrawal, whereas crab chemical cues induced thicker, more rotund shells, which were more resistant to crushing. Shell phenotypes that reduced susceptibility to one predator increased susceptibility to the other, indicating a functional tradeoff. Snails in the combined predator treatment showed a directional response to the more dangerous crab predator. Although crabs induce thicker shells, this response is a passive by-product of reduced feeding and growth rather than a direct physiological response to predation risk. My results provide an intriguing and previously unknown mechanism for inducible defenses and suggest that prey can distinguish between functionally different predators and prioritize conflicting morphological responses according to risk in multiple predator environments.