Spots or stripes make no difference to fish predators

22 August 2018




How fast do predators learn what they can and cannot eat by how their prey looks? It’s not spots and stripes, according to QBI scientists, but the edge around a pattern that give the best clues.

PhD student Naomi Green, Dr Karen Cheney, and Professor Justin Marshall from QBI and the UQ School of Biological Sciences found the amount of pattern edge – the outline of pattern elements, such as circles or lines – was a critical factor in determining how quickly predators understood visual cues.

The team found that triggerfish learned warning patterns significantly faster when shown visuals with a greater amount of pattern edge. There was no evidence, says Dr Cheney, that pattern type, the number of repetitive elements, or amount of coloured area affected predator learning.

Patterns help to uncover nature’s secrets

Why is this important? For biologists, the role and importance of patterns and markings in predator deterrence remain one of the lingering mysteries of nature. 

“We set out to help answer one of the pervading questions in the field of behavioural ecology: Why do animals demonstrate such a wide variety of visual cues, and which ones are more effective in predator learning?” Dr Cheney said.

“We just don’t know why there’s such a diversity of colour patterns in, for example, coral reef fish and nudibranchs, and it’s unclear how predators are using these visual images to make decisions about what they’re attacking and what they leave alone.

“So that was the basis of Naomi’s project – does it matter if you have spots or stripes, and does that affect the way that toxicity is being learned?”

Ms Green said the research was important in advancing knowledge in the evolution of colour warning signals and predator psychology.

“You often see spots and you see stripes in nature – but in our study it didn’t seem to affect learning, as long as the amount of edge was the same,” she said.

“If it was a difference between, say, spots and stripes that affected toxicity learning, then the fish would be learning spots easier than stripes or vice versa – but we didn’t find that. It was the edge effect that was the most important.”

In the experiment, wild-caught triggerfish were trained to peck stimuli to receive food. Plain, white stimuli saw the fish rewarded with squid, while patterned, coloured stimuli gave the fish unpalatable food they spat out.

The study was published in the journal Behavioral Ecology and supported by the Australian Research Council.