Antipredator defenses are ubiquitous and diverse. Ink secretion of sea hares (Aplysia) is an antipredator defense acting through the chemical senses of predators by different mechanisms. The most common mechanism is ink acting as an unpalatable repellent. Less common is ink secretion acting as a decoy (phagomimic) that misdirects predators' attacks. In this study, we tested another possible mechanism – sensory inactivation – in which ink inactivates the predator's reception of food odors associated with would-be prey. We tested this hypothesis using spiny lobsters, Panulirus argus, as model predators. Ink secretion is composed of two glandular products, one being opaline, a viscous substance containing concentrations of hundreds of millimolar of total free amino acids. Opaline sticks to antennules, mouthparts and other chemosensory appendages of lobsters, physically blocking access of food odors to the predator's chemosensors, or over-stimulating (short term) and adapting (long term) the chemosensors. We tested the sensory inactivation hypotheses by treating the antennules with opaline and mimics of its physical and/or chemical properties. We compared the effects of these treatments on responses to a food odor for chemoreceptor neurons in isolated antennules, as a measure of effect on chemosensory input, and for antennular motor responses of intact lobsters, as a measure of effect on chemically driven motor behavior. Our results indicate that opaline reduces the output of chemosensors by physically blocking reception of and response to food odors, and this has an impact on motor responses of lobsters. This is the first experimental demonstration of inactivation of peripheral sensors as an antipredatory defense.
All authors were involved in designing the experiments and writing the article, and T.L.-C. and J.F.A. executed the experiments.
Supplementary material available online at http://jeb.biologists.org/cgi/content/full/216/8/1364/DC1
No competing interests declared.
This work was supported by National Science Foundation grants IOS-0614685 and IOS-1036742 to C.D.D.
- © 2013.