Do anemonefishes use molecular mimicry to avoid being stung by host anemones?

Abstract

Anemonefishes are known to have a protective mucous coat that allows them to contact the tentacles of their host anemone without being stung. There are two conflicting hypotheses as to the source and biochemical properties of this mucous coating. One hypothesis proposes that anemonefishes acquire anemone substances from their hosts during the behavioral process of acclimation, that protect the fish from being stung. Anemonefishes are considered to use anemone mucus as “chemical camouflage” or “macromolecular mimicry” to avoid recognition as “not-self” by the anemone, and possible subsequent stinging. Another hypothesis is that anemonefishes produce their own protective mucus coat, which lacks substances that elicit cnida (nematocyst and spirocyst) discharge by their hosts. The present study used immunological techniques to test whether the anemonefish Amphiprion clarkii (Bennett) (which was innately protected from two of the anemones used in the present study) has a mucous coat that resembles the external mucus of anemones. Polyclonal antibodies were prepared to the mucus of four species of anemones [ Heteractis crispa, (Ehrenberg) Stichodactyla haddoni (Saville-Kent), Macrodactyla doreenensis (Quoy and Gaimard), and Condylactis gigantea (Weinland)]. Ouchterlony (double immunodiffusion) tests showed that different antigens were present in the mucus of the four anemone species. Anemone antigens were not detected in the mucous coating of either naive (fish that had never before encountered sea anemones) or associated (those living with sea anemones) anemonefishes in Ouchterlony tests. However, more sensitive ELISA (enzyme-linked immunosorbent assay) tests showed that anemone mucus antigens were present in the mucous coating of associated anemonefish, but not naive fish. This showed that an innately protected A. clarkii does not produce a mucus coat that is biochemically similar to that of anemones, but that the same fish does acquire anemone substances in its mucus coat when it associates with anemones in aquaria. It remains to be shown whether these anemone substances actually provide the initial protection for those anemonefishes that must undergo acclimation behavior in order to keep from being stung by their host sea anemones, or additional protection for innately protected fishes.