Pondering the humble Zoantharian

I have a question I have been wondering about for a long time, and have not been able to find even a scrap of information about online. Most zoantharians, an order of colonial anemone-like cnidarians, possess a neurotoxin known as palytoxin in their tissues. Palytoxin is highly toxic, and is the second most potent naturally-occurring neurotoxin known to man. Most species contain relatively low levels of this toxin, but some, especially those in the genus Palythoa, contain high concentrations of palytoxin. Being sessile and otherwise defenseless, it may seem obvious the purpose of this toxin, to deter predators. However, from what I have read, fish and invertebrates seem to be immune to palytoxin. Many reef fish, such as marine angelfishes, feed on zoantharians without issue. I can’t think of any animals that would consume zoantharians besides fish and invertebrates. Clearly this toxin is important to zoantharians, as it it so widespread in the order, and so highly toxic. So here is my question - what is the purpose of palytoxin in zoantharians, if their predators are immune to the toxin?

Could it perhaps be a holdover adaptation that was useful against a now-extinct predator?

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One explanation is that it’s an “arms race”. Presumably, Palythoa, with its toxic metabolite, was distasteful or dangerous to consume at some point in the evolutionary past, but now various populations of predators have adapted–that is, those genetic strains of the predators which did not die from ingesting Palythoa subsequently propagated and spread in the population. Despite losing its predator-deterrent effect, the compound in Palythoa may have some yet unrecognized physiological benefit, so it may be retained. A predictable next step in this arms race is that some mutation in Palythoa will create a slightly different version of the compound which will have a renewed deterrent effect on predators…and on and on it goes.


Ah, that makes a lot of sense, thankyou!!

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