Cue reliability, risk sensitivity and inducible morphological defense in a marine snail

Abstract

Reliable cues that communicate current or future environmental conditions are a requirement for the evolution of adaptive phenotypic plasticity, yet we often do not know which cues are responsible for the induction of particular plastic phenotypes. I examined the single and combined effects of cues from damaged prey and predator cues on the induction of plastic shell defenses and somatic growth in the marine snail Nucella lamellosa. Snails were exposed to chemical risk cues from a factorial combination of damaged prey presented in isolation or consumed by predatory crabs (Cancer productus). Water-borne cues from damaged conspecific and heterospecific snails did not affect plastic shell defenses (shell mass, shell thickness and apertural teeth) or somatic growth in N. lamellosa. Cues released by feeding crabs, independent of prey cue, had significant effects on shell mass and somatic growth, but only crabs consuming conspecific snails induced the full suite of plastic shell defenses in N. lamellosa and induced the greatest response in all shell traits and somatic growth. Thus the relationship between risk cue and inducible morphological defense is dependent on which cues and which morphological traits are examined. Results indicate that cues from damaged conspecifics alone do not trigger a response, but, in combination with predator cues, act to signal predation risk and trigger inducible defenses in this species. This ability to "label" predators as dangerous may decrease predator avoidance costs and highlights the importance of the feeding habits of predators on the expression of inducible defenses.

Risk recognition and variability in escape responses among intertidal molluskan grazers to the sun star Heliaster helianthus

“…Several laboratory studies have shown that prey can assess and respond to varying predation risks according to whether the predator feeds on alternative prey (e.g. Hagen et al 2002, Shin et al 2009, Bourdeau 2010. Our results suggest that under natural conditions of multiple cues and risks, this fine assessment may not be possible or effective in these 4 grazer species.…”

Size matters for risk assessment and resource allocation in bivalves

“…For example, predator-induced behavioral changes such as a reduction in prey foraging time (Turner 2004, Large & Smee 2010 or feeding cessation (Smee & Weissburg 2006, Naddafi et al 2007 can minimize predation risk, but may ultimately lower growth and fecundity (Relyea 2001, 2002, Fassler & Kaiser 2008, Bourdeau 2010. Constant exposure to risk may also decrease body size and increase the likelihood of being consumed (Edeline et al 2010).…”

Whelks induce an effective defense against sea stars

“…An alternative explanation is that the aspect ratio of the shell responds more slowly than changes in the soft tissue of the body and foot associated with increased retractability. Our experiment lasted 30 d whereas Bourdeau's experiment lasted 70 d, and the duration of our experiment was shorter than any experiment that has demonstrated predator-induced chan ges in the shell of Nucella lamellosa (Appleton & Palmer 1988, Palmer 1990, Bourdeau 2009, 2010a, 2010b, 2011. Given that snails grew very little in our experiment and the coiling of the shell means that altering width initially will alter height later, the latter hypothesis seems more plausible.…”

“…Before adding more whelks to the predator compartment, we removed any living whelks and remains of whelks consumed during the week. We added whelks to the predator compartment because cues from the consumption of conspecifics by predators can induce stronger responses in whelks (Appleton & Palmer 1988, Bourdeau 2010a, Grason & Miner 2012, although this makes the source of cue unclear. The experiment ended after 30 d, and 3 whelks died during the induction experiment (2 from the sea star treatment and 1 from the control).…”