Interspecific variation in palatability suggests cospecialization of antipredator defenses in sea hares

Abstract

Prey species often deploy different kinds of antipredator defenses, which can interact with each other in ways that are not yet completely understood. Much research into these interactions has utilized gastropod mollusks, usually focusing (in part) on the protective utility of the gastropod shell. This makes the evolutionary reduction of the shell in the opisthobranch gastropods (marine slugs) particularly interesting. This loss of protective function of the shell is associated with the evolution of alternative defenses. Particularly well studied are chemical defenses, especially those using secondary metabolites derived from food resources. As a first step toward understanding interspecific variation in the deployment of multiple defenses, we compared the passive chemical defenses of 3 opisthobranchs (Aplysia californica, Phyllaplysia taylori, and Dolabrifera dolabrifera; hereafter referred to by their genus name). We homogenized the skin and body wall into standardized food pellets, and assayed the palatability of these pellets by measuring their consumption by a common intertidal hermit crab, Pagurus samuelis. This assay revealed significant variation in palatability. Pellets made from the skin and body wall of Phyllaplysia and Dolabrifera had higher palatability, indicating low levels of chemical protection, while pellets from Aplysia showed a 2-fold lesser palatability, indicating greater chemical protection. This phylogenetic variation in palatability is similar to previously reported variation in behavioral sensitization. Although the role of sensitization as a possible antipredator defense is yet poorly understood, these results on palatability raise the possibility that opisthobranchs may cospecialize defenses across species.

Ecology- and Bioassay-Guided Drug Discovery for Treatments of Tropical Parasitic Disease: 5α,8α-Epidioxycholest-6-en-3β-ol Isolated from the Mollusk Dolabrifera dolabrifera Shows Significant Activity against Leishmania donovani

“…Our results suggest that compound 1 may provide a chemical defense for D. dolabrifera. While palatability studies with pellets derived from the skin and body wall of D. dolabrifera suggested low levels of chemical protection [32], our finding that compound 1 is concentrated in the digestive gland of D. dolabrifera suggests that their study likely overlooked the major source of a compound that could provide chemical defense to the organism.…”

Marine chemical ecology in benthic environments

“…The body tissues of A. californica are also unpalatable to predators. 174 Food pellets made from the skin and body wall tissue of A. californica were signicantly less palatable to hermit crabs (Pagurus samuelis) compared to two other sea hares, Phyllaplysia taylori and Dolabrifera dolabrifera.…”

Shifts in attack behavior of an important kelp forest predator within marine reserves

“…Individuals of A. californica de ploy active (i.e. ink and opaline; Kicklighter et al 2005, Derby & Aggio 2011 as well as passive (Takagi et al 2010) chemical defenses to make them effectively unpalatable to most predators (see review by Carefoot 1987). If in deed lobsters attacked sea hares only inside reserves, then this would (1) be consistent with optimal diet theory, (2) constitute previously unreported evidence that reserves change attack behavior of protected predators, and (3) highlight the need to consider changes in predator behavior when assessing the ecological consequences of marine protected areas.…”