Crustaceans as Powerful Models in Aquatic Chemical Ecology

Crustaceans use chemical cues to find and assess mates, signal dominance, recognize known conspecifics, find favored foods and appropriate habitats, and assess threats such as the presence of predators. The behavior demonstrating these cues is dramatic (e.g., males of some species will guard and try to copulate with sponges, rocks, or even other males treated with water holding receptive, conspecific females), but the specific chemicals eliciting these behaviors have rarely been unambiguously described. Here I discuss the known compounds that affect crustacean behaviors and note that identifying active chemical signals and cues may be a challenge because these chemicals may: (1) occur at low concentrations in a media holding many other metabolites, (2) be complex blends instead of particular pure compounds – and it may be the blend itself (the specific ratio of different signaling molecules) that carries information, (3) be “combination-lock” cascades of chemical signals and cues that have to occur in the correct order to generate a critical behavior, and (4) have been selected as critical molecules eliciting behavior because they rapidly degrade, thus preventing maladaptive behavior based on old data. These potential traits will make separation and structural determination difficult. Despite many signals and cues being delivered via water, there are several examples of cuing compounds being lipidsoluble; it is important for biologists to realize that even lipids dissolve to some degree in water and can thus function as waterborne cues. Because of the critical role that crustaceans play in marine and freshwater food webs, the effects of chemical mediation of crustacean behavior can reach far beyond the direct effects on crustaceans to impact community organization and even ecosystem-level processes.