There was somewhat less concordance between these two indicators and neurotoxicity although this was insufficient to reduce the statistical significance of the estimates. We may speculate that different mechanisms of toxic action may explain these findings and that further work is necessary to examine this possibility. Toxicity ranking did not correspond to anemone phylogeny. For example, most of the Heteractis species were found to be relatively low in haemolytic toxicity yet one congener, H. magnifica, had the second highest toxicity. Similarly, S. gigantea had a much lower haemolytic effect than S. haddoni. One study which may help to explain this lack of phylogenetic correspondence purified 2 cytolysins, Sticholysin I and Sticholysin II from the anemone Stichodactyla helianthus, and showed that despite a high degree of amino acid sequence homology the cytolysins Farrerol differed significantly in their haemolytic activity. Therefore, even small changes in the amino acid sequence can result in significant modifications of toxicity among related species. The curved distribution characterising the relationship between overall anemone toxicity and number of anemonefish BRD32048 associates demonstrates that anemones with comparatively low or high toxicity, have fewer fish associates and anemone species with moderate toxicity have the highest number of fish symbionts. In fact, it appears that the most highly sought after anemones have a toxicity that falls within the middle of the toxicity range, suggesting that moderate toxicity may be optimal for anemonefish survival and reproduction. High predation pressure in the tropical marine environment exerts strong selective pressure on sessile or slow-moving organisms to evolve defense mechanisms,. Tropical anemones possess three defense strategies which may not be mutually exclusive; chemical defense, behavioural defense, and a symbiotic partner that provides protection. C. adhaesivum and H. malu, the anemone species which have a single anemonefish associate, are commonly found without anemonefish in the wild,. This observation requires explanation as these anemone species cannot be solely relying on anemonefish for protection against grazers.