Meeting Abstract

P1.44  Friday, Jan. 4  Hermit-crab assay reveals heterogeneity in deterrence by actively secreted chemical defenses in Aplysia californica GOMEZ, S.F.*; TAKAGI, K.K.; WRIGHT, W.G.; Chapman University; Chapman University; Chapman University gomez131@mail.chapman.edu

Chemical defenses against predators are a hallmark of physically unprotected prey. For example, the shell-less marine gastropods have a range of such defenses, including chemicals that are actively released in response to predation. The sea hare, Aplysia californica, releases two kinds of secretions; ink and a viscous opaline. This raises a question of their relative functions. Ink is generally a more effective deterrent against a variety of predators, whereas opaline is weakly deterrent at best (Nusnbaum and Derby 2010). Research on lobsters, however, demonstrated a significantly stronger deterrence of opaline than that of ink (Aggio and Derby 2008). These latter results suggest a heterogenous function of ink and opaline across consumer species. To further explore the relative deterrency of Aplysia ink and opaline, the present study utilized a powerful feeding assay using the hermit crab, Pagurus samuelis. Similar to lobsters, we found that hermit crabs were deterred significantly more by opaline than by ink. As a step toward identifying the deterrent chemicals in opaline, we obtained water soluble and insoluble fractions (Charles Derby, GSU, Atlanta). Hermit crabs were deterred by the water-soluble fraction only. Further separation (Derby lab) into a mycosporine-like amino acids (MAAs) fraction and a MAA-free fraction revealed that both had the same deterrent activity. These results support the hypothesis that the relative deterrency of ink and opaline is specific to the consumer. Such heterogeneity suggests two adaptive hypotheses: 1) Ink has evolved to deter fish predators, while opaline has evolved to deter crustaceans, or 2) Deterrents synthesized de novo, may be more tightly tuned to sympatric, co-evolving predators.