Insects are scared to death of fish

Oct 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: Archaeological, genetic evidence expands views of domestication

add to favorites email to friend print save as pdf

Related Stories

Time of Day Tempers Tadpoles' Response to Predators

Aug 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

Sep 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 ...

Predators do more than kill prey

Jan 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

Jun 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 ...

Recommended for you

Orchid named after UC Riverside researcher

8 hours ago

One day about eight years ago, Katia Silvera, a postdoctoral scholar at the University of California, Riverside, and her father were on a field trip in a mountainous area in central Panama when they stumbled ...

In sex-reversed cave insects, females have the penises

10 hours ago

Researchers reporting in the Cell Press journal Current Biology on April 17 have discovered little-known cave insects with rather novel sex lives. The Brazilian insects, which represent four distinct but re ...

Fear of the cuckoo mafia

10 hours ago

If a restaurant owner fails to pay the protection money demanded of him, he can expect his premises to be trashed. Warnings like these are seldom required, however, as fear of the consequences is enough to ...

User comments : 5

Adjust slider to filter visible comments by rank

Display comments: newest first

DavidMcC
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! :)
TrevS
not rated yet Oct 30, 2011
Is there an evolutionary benefit to this?
DavidMcC
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!).
DavidMcC
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).

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

More news stories

Deadly human pathogen Cryptococcus fully sequenced

Within each strand of DNA lies the blueprint for building an organism, along with the keys to its evolution and survival. These genetic instructions can give valuable insight into why pathogens like Cryptococcus ne ...

Better thermal-imaging lens from waste sulfur

Sulfur left over from refining fossil fuels can be transformed into cheap, lightweight, plastic lenses for infrared devices, including night-vision goggles, a University of Arizona-led international team ...

Hackathon team's GoogolPlex gives Siri extra powers

(Phys.org) —Four freshmen at the University of Pennsylvania have taken Apple's personal assistant Siri to behave as a graduate-level executive assistant which, when asked, is capable of adjusting the temperature ...