Insects are scared to death of fish

October 27, 2011
This is a dot-tailed whiteface dragonfly. Biologists at the University found that the mere presence of a predator causes enough stress to kill a dragonfly, even when the predator cannot actually get at its prey to eat it. Credit: Shannon J. McCauley

The mere presence of a predator causes enough stress to kill a dragonfly, even when the predator cannot actually get at its prey to eat it, say biologists at the University of Toronto.

"How prey respond to the of being eaten is an important topic in ecology, and we've learned a great deal about how these responses affect predator and prey interactions," says Professor Locke Rowe, chair of the Department of Ecology and (EEB) and co-principal investigator of a study conducted at U of T's Koffler Scientific Reserve.

"As we learn more about how respond to – whether it's the presence of predators or stresses from other natural or human-caused disruptions – we increasingly find that stress brings a greater risk of death, presumably from things such as infections that normally wouldn't kill them," says Rowe.

Shannon McCauley, a post-doctoral fellow, and EEB professors Marie-Josée Fortin and Rowe raised juvenile dragonfly larvae (Leucorrhinia intacta) in aquariums or tanks along with their predators. The two groups were separated so that while the dragonflies could see and smell their predators, the predators could not actually eat them.

"What we found was unexpected - more of the dragonflies died when predators shared their habitat," says Rowe. Larvae exposed to predatory fish or aquatic insects had survival rates 2.5 to 4.3 times less than those not exposed.

In a second experiment, 11 per cent of larvae exposed to fish died as they attempted to metamorphose into their adult stage, compared to only two per cent of those growing in a fish-free environment. "We allowed the juvenile dragonflies to go through metamorphosis to become adult dragonflies, and found those that had grown up around predators were more likely to fail to complete metamorphosis successfully, more often dying in the process," says Rowe.

The scientists suggest that their findings could apply to all organisms facing any amount of stress, and that the experiment could be used as a model for future studies on the lethal effects of stress.

The research is described in a paper titled "The deadly effects of 'nonlethal' ", published in Ecology and highlighted in Nature this week. It was supported by grants to Fortin and Rowe from the Canada Research Chairs program and the Natural Sciences and Engineering Research Council of Canada, and a post-doctoral fellowship awarded to McCauley.

Explore further: Time of Day Tempers Tadpoles' Response to Predators

Related Stories

Time of Day Tempers Tadpoles' Response to Predators

August 10, 2006

To a tiny tadpole, life boils down to two basic missions: eat, and avoid being eaten. But there's a trade-off. The more a tadpole eats, the faster it grows big enough to transform into a frog; yet finding food requires being ...

Salmon can sniff out predators

September 13, 2011

Salmon know when their most common predator is around, because they can tell that it's eaten salmon before, new research shows. Young fish can do this too, even if they've never encountered that particular predator before.

Predators do more than kill prey

January 17, 2008

The direct effect predators have on their prey is to kill them. The evolutionary changes that can result from this direct effect include prey that are younger at maturity and that produce more offspring.

Scientists uncover an unhealthy herds hypothesis

June 23, 2011

Biologists worldwide subscribe to the healthy herds hypothesis, the idea that predators can keep packs of prey healthy by removing the weak and the sick. This reduces the chance disease will wipe out the whole herd, but could ...

Recommended for you

Scientists discover new plant in Shetland

August 16, 2017

Scientists at the University of Stirling have discovered a new type of plant growing in Shetland - with its evolution only having occurred in the last 200 years.


Adjust slider to filter visible comments by rank

Display comments: newest first

1 / 5 (1) Oct 28, 2011
How do they know it's psychological stress and not just plain old poisoning from the smell? They don't seem to worry about insectivorous birds, do they?
EDIT: In other words, the "stress" need not be psychological. In fact, if it was, wouldn't they try to fly away from it? Even if they did, it could be that they just can't stand the smell of fish! :)
not rated yet Oct 30, 2011
Is there an evolutionary benefit to this?
1 / 5 (1) Oct 31, 2011
Is there an evolutionary benefit to this?

If the "stress" on the dragonfly is toxic stress rather than pstychological stress, then it might well be an evolutionary benefit to the fish, because the poisoning helps it to hunt. If, on the other hand, it is just a side-effect of the dragon fly's "fear" of the fish, then it would be the down side of the fly's "evolutionary counter-measure" to predation - the fear that is a precursor to flight (flight by flight, that is!).
not rated yet Nov 16, 2011
Discussing this on a different site, I have realised that there were several issues with this article. I may well get another "1" for this, but I suspect that what is really happening here is that the exposed dragonfly nymph is being denied the chance of feeding by the presence of the fish, because, normally, the nymph would stop hunting in order to stay still to avoid being spotted by the fish. However, in this case, the fish never goes away. Thus, the insect isn't dying of fright (which has never been shown to happen in insects).

not rated yet Nov 16, 2011
Maybe the journalist who composed the title of this article should also get a "1".

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.