Marina Wang

Marina is a freelance science writer based in Calgary, AB. She has a Bachelor of Science degree from the University of British Columbia and a Master of Journalism degree from Carleton University and has previously written for Canadian Geographic and Space Q.

Guppies react to stress cues: the bigger the group, the bigger the response

April 2, 2019 | 3 minute read

Following the crowd like sheep is a common adage, but it turns out sheep aren’t the only critters in the animal kingdom that tend to follow the crowd.

In a new study from the Canadian Journal of Zoology, researchers examined the defensive behaviour of guppies in response to predator cues and found that the larger the crowd, the stronger the fear response.

Furthermore, the researchers wanted to know if this pattern held true between different species of fish—and to their surprise, it didn’t. The guppies were also exposed to fear signals from convict cichlids and found that there was no difference in response between stronger and weaker cues from the different species.

“Originally we were testing whether these were species-specific cues and I thought that they were going to be generalized,” said Jack Goldman, lead author of the paper. “When I found the results it was extremely surprising and interesting.”

Under stress, many aquatic animals will produce predator response cues—chemical signals secreted into the environment that other animals can pick up on. These response cues are broadly split into damage-released alarm cues, released from the skin from physical damage, and disturbance cues that are thought to be metabolic by-products released in the urine or through the gills when fish are under stress. While damage-release cues are better understood, disturbance cues are less so.

The researchers aimed to test three hypotheses: (1) To confirm that Trinidadian guppies did indeed produce disturbance cues, (2) that a higher concentration of these cues from more guppies would elicit a stronger defensive response, and (3) that the disturbance cue is generalized, so guppies should also have a defensive response regardless of the species producing the disturbance cue.

“Earlier studies had shown that it was a generalized cue, but no one had tested the effect of the amount of cue on the response between species.  We thought if it were fully generalized, we should get similar responses between species, but we didn’t,” said Goldman.

In the paper, researchers put guppies in tanks in groups of either 10 or 20. They then scared the fish using a model predator and collected water from the treatment tanks. A small sample of the treatment water was then placed in new tanks with three guppies in them to see how they would react to the new disturbance cues in the water.

When scared, guppies will exhibit shoaling behaviour in which they group together in defense. And sure enough, guppies that had the higher concentration of disturbance cues showed more shoaling behaviour.

Guppies were also exposed to stress cues from convict cichlids. (Photo | Wikimedia Commons)

Next, researchers wanted to test if the guppies would have the same response to disturbance cues from convict cichlids. Similarly, researchers put 10 cichlids in one tank and 20 in another and scared the fish with a model predator.

Unlike the previous test, the guppies displayed no significant difference in shoaling behaviour when exposed to a high versus low dose of cichlid disturbance cue, proving that these signals are at least partly species specific.

“These cues could be extremely important and have been generally overlooked by ecologists,” said Goldman. Goldman said that these findings could draw more attention to disturbance cues and their importance to predator–prey relations.

“There are a lot more questions to be answered, and specifically, to find what this cue actually is,” he said. Goldman also said future studies could examine if the cue is simply a metabolic by-product or part of a more complex communication system. Studies could also be done to determine how other environmental factors might affect responses to disturbance cues.

Read the full study: Does donor group size matter? The response of Trinidadian guppies and Convict cichlids to disturbance cues from conspecific and heterospecific donors in the Canadian Journal of Zoology.

Marina Wang

Marina is a freelance science writer based in Calgary, AB. She has a Bachelor of Science degree from the University of British Columbia and a Master of Journalism degree from Carleton University and has previously written for Canadian Geographic and Space Q.