Media Releases

Insects are scared to death of fish

October 27, 2011

University of Toronto biologists find higher mortality among dragonflies exposed to undue stress

TORONTO, ON –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 fear 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 Evo­lu­tion­ary Biol­o­gy (EEB) and co-prin­ci­pal inves­ti­ga­tor of a study con­duct­ed at U of T’s Kof­fler Sci­en­tif­ic Reserve.

“As we learn more about how ani­mals respond to stress­ful con­di­tions – 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’ preda­tors”, 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.

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For more infor­ma­tion, please con­tact:

Marie-Josée Fortin
Depart­ment of Ecol­o­gy and Evo­lu­tion­ary Biol­o­gy
Uni­ver­si­ty of Toron­to

Shan­non McCauley
Bio­log­i­cal Sci­ences Depart­ment
Cal­i­for­nia Poly­tech­nic State Uni­ver­si­ty
805–756-2498 (b)
651–280-5668 ©

Sean Bet­tam
Com­mu­ni­ca­tions, Fac­ul­ty of Arts & Sci­ence
Uni­ver­si­ty of Toron­to