Searching for a toxic key to unlock the mystery of anemonefish and anemone symbiosis.

Jeanne E Young,Karen Burke Da Silva,Athanassios C Tsikliras,John W Edwards,Anita M Nedosyko

doi:10.1371/journal.pone.0098449

Abstract

Twenty-six species of anemonefish of the genera Amphiprion and monospecific Premnas, use only 10 species of anemones as hosts in the wild (Families: Actiniidae, Stichodactylidae and Thalassianthidae). Of these 10 anemone species some are used by multiple species of anemonefish while others have only a single anemonefish symbiont. Past studies have explored the different patterns of usage between anemonefish species and anemone species; however the evolution of this relationship remains unknown and has been little studied over the past decade. Here we reopen the case, comparing the toxicity of crude venoms obtained from anemones that host anemonefish as a way to investigate why some anemone species are used as a host more than others. Specifically, for each anemone species we investigated acute toxicity using Artemia francisca (LC50), haemolytic toxicity using ovine erythrocytes (EC50) and neurotoxicity using shore crabs (Ozius truncatus). We found that haemolytic and neurotoxic activity varied among host anemone species. Generally anemone species that displayed greater haemolytic activity also displayed high neurotoxic activity and tend to be more toxic on average as indicated by acute lethality analysis. An overall venom toxicity ranking for each anemone species was compared with the number of anemonefish species that are known to associate with each anemone species in the wild. Interestingly, anemones with intermediate toxicity had the highest number of anemonefish associates, whereas anemones with either very low or very high toxicity had the fewest anemonefish associates. These data demonstrate that variation in toxicity among host anemone species may be important in the establishment and maintenance of anemonefish anemone symbiosis.

Highlights

Marine animals are amongst the most venomous species on earth and the Cnidaria in particular are well known for the potency of their stings
Host venoms ranged significantly with the venom of S. haddoni found to be the most potent with 50% lysis occurring at 0.02 mg/ mL and H. malu having the lowest haemolytic activity with 50% lysis occurring above 65 mg/mL, at which point undiluted venom extract was applied and an exact EC50 could not be obtained (Table 2)
Crude venom from nine anemone species that act as hosts for anemonefish showed significant differences in haemolytic and acute toxicity

Summary

Introduction

Marine animals are amongst the most venomous species on earth and the Cnidaria in particular are well known for the potency of their stings. Sea anemones are sessile organisms that possess a variety of proteic substances (such as peptides, proteins, enzymes, and proteinase inhibitors, see [1]) for protection, for hunting, and competitive interactions. The mechanisms involved in protecting anemonefish from anemone venom has been examined by multiple authors How anemonefish acquire immunity from stinging tentacles remains uncertain, it is generally agreed that the fish’s mucus plays an important role in its protection either through a blocking mechanism or through inhibition by mimicry (see [14] for a recent review)

Methods

Results

Conclusion