Sea slugs taste horrible – predators remember that by memorizing a tiny detail in their appearance

Predators typically don‘t eat toxic animals. That is a very interesting mechanism, because it allows some animals to avoid getting eaten and other – to avoid poisoning. You probably already know that brightly coloured animals are generally toxic, but now scientists from the University of Queensland explained how bright colours are used to deter potential threat.

These sea slugs have varying patterns, which are meant to scare predators away. Image credit: Sylke Rohrlach via Wikimedia(CC BY-SA 2.0)

Scientists were thinking that these visual signals, indicating that the animal is toxic, cannot change much over time, because predators may get confused and kill the animal anyway. Species in question were sea slugs, or nudibranchs, which had bright colour patterns that could easily change over time, hindering predator’s ability to recognize this animal as dangerous when eaten. However, this study revealed that coloration actually does change over time, but that does not compromise protection from the predators. It is because fish that typically would eat these slugs learn to recognise the consistent parts of the colour pattern.

Red spots on this sea slug are always changing, which should be a disadvantage. However, a yellow rim bordering a white area basically never varies from one individual to another. Scientists found that fish, such as triggerfish Rhinecanthus aculeatus, basically do not care about red spots and learn only the yellow rim. This seems counter intuitive, because red spots are certainly easier to notice, but the yellow rim doesn’t vary too much from one animal to another.

For humans it is very easy to identify species, but animals don’t have such complex visual interpretation skills and so they rely on things they can memorize. Dr Karen Cheney, one of the authors of the research, said: “Natural selection may act on parts of the colour pattern in very different ways, allowing for the yellow rim to be stable, but the red spots to be highly variable”.

Interestingly, these sea slugs, Gonibranchus splendidus, actually make themselves poisonous themselves – they are not born that way. They consume a lot of sea sponges, which makes them distasteful to predators. And so predators eat them sometimes with varying consequences and learn that they taste horrible and never eat them again. Colour patterns help remembering, which animals should not be consumed.


Source: University of Queensland

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