Escape responses of coral reef fish obey simple behavioral rules

November 12, 2018, University of California - Santa Cruz
In a wide range of coral reef fish species, a sequence of well-defined decision rules generate evasion behavior to escape a perceived threat. Credit: Stella Hein

The escape response to evade perceived threats is a fundamental behavior seen throughout the animal kingdom, and laboratory studies have identified specialized neural circuits that control this behavior. Understanding how these neural circuits operate in complex natural settings, however, has been a challenge.

A new study led by researchers at UC Santa Cruz and NOAA Fisheries overcame this challenge using a clever experimental design to record and analyze escape responses in . The results, published November 12 in Proceedings of the National Academy of Sciences, reveal how a sequence of well-defined decision rules generates evasion behavior in a wide range of coral reef species.

"We took an approach used in laboratory studies into a complex, natural environment and found that the same behavioral mechanisms seem to apply. A set of simple rules are combined in different ways to generate a rich suite of behaviors to accomplish this fundamental goal: to avoid being killed," said first author Andrew Hein, an assistant researcher at the UC Santa Cruz Institute of Marine Sciences and research ecologist at the NOAA Fisheries Lab in Santa Cruz.

The coral reef fish in the study feed on algae in shallow reef flats, where they are vulnerable to predators such as moray eels and reef sharks. To simulate a , the researchers employed a widely used visual called the looming stimulus, a black dot that grows in size slowly and then rapidly, creating the illusion of a rapidly approaching object. A waterproof tablet computer deployed on a coral in Mo'orea, French Polynesia, played the looming stimulus, while video cameras recorded the responses of fish that swam into the area in front of the tablet.

The researchers then used computer vision technology to analyze the video. Automated tracking and a method known as "ray casting," originally developed by video game designers, allowed them to reconstruct what each fish was seeing as it decided whether or not to flee from the threat. They found that fish initiated escape maneuvers in response to the perceived size and expansion rate of the threat stimulus using a decision rule that matched the dynamics of known loom-sensitive .

"This same behavioral circuit that neuroscientists identified in lab studies seems to be operating in the more complex natural environment," Hein said. "But we also found something new: the sensitivity to the looming stimulus gets tuned up or down depending on the locations of other fish. If an individual is the closest one to the stimulus, it is much more likely to flee than if there is another fish between it and the threat."

A third factor in the escape response was the location of a safe place to shelter, offered by a mounding coral alongside the experimental area. The initial response to the stimulus is to quickly turn away from the threat, but almost immediately the fish then began turning toward the shelter and swam directly toward it.

"When you look at the paths they take, it looks like spaghetti—they're all different—but the analysis shows they're all generated by the same simple set of behavioral rules," Hein said.

Explore further: Fish social lives may be key to saving coral reefs

More information: Andrew M. Hein el al., "Conserved behavioral circuits govern high-speed decision-making in wild fish shoals," PNAS (2018). www.pnas.org/cgi/doi/10.1073/pnas.1809140115

Related Stories

Fish social lives may be key to saving coral reefs

April 10, 2017

The social eating habits of fish may play a central role in protecting coral reefs, according to a study from the University of California, Davis, published April 10 in the journal Proceedings of the National Academy of ...

Recommended for you

Researchers find positive visual contagion in Barbary macaques

December 12, 2018

A pair of researchers at the University of Roehampton has found that captive Barbary macaques are capable of engaging in positive visual contagion—a behavior normally only seen in humans. In their paper published in Proceedings ...

Hot possums risk losing their homes

December 12, 2018

As our world is warming under climate change, heat waves are becoming more frequent and intense, yet the vulnerability of our wildlife to such events is poorly understood. New research from Australia's Wet Tropics indicates ...

The real history of quantum biology

December 12, 2018

Quantum biology, a young and increasingly popular science genre, isn't as new as many believe, with a complicated and somewhat dark history, explain the founders of the world's first quantum biology doctoral training centre.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.