Dragonflies and damselflies also suffer from high heat – Liberation


Acting for the living: “the Wandering Albatross”

Act for the livingdossier
Every week on our site, “The Wandering Albatross”, an ecological chronicle by David Grémillet, CNRS research director at the Center for Functional and Evolutionary Ecology in Montpellier. Today, the impact of global warming on dragonflies and damselflies.

The summer heat wave never ends and all nature suffers. Vegetation scorches under the sun, trees and animals die of thirst. Mammals and birds are particularly affected as they try to maintain a stable internal temperature; around 37°C for humans, and 40°C for birds. They are therefore equipped with a body air conditioning system based on perspiration and panting, which is very efficient but consumes energy and water. On the contrary, most fish, reptiles, amphibians and invertebrates have a body temperature that tends to follow that of the environment, and one might think that scorching heat does not affect them.

Nothing could be further from the truth with regard to insects, as demonstrated by a century of research on their physiology (1). Indeed, many species among these six-legged creatures flee too high temperatures. This is the case of dragonflies and damselflies (2), these sublime flying predators, according to a recent study carried out in the Colombian Andes (3). In Tatamá National Park, Cornelio Bota-Sierra (Institute of Ecology, Veracruz, Mexico) and his colleagues studied the thermal preferences of 54 species of dragonflies and damselflies. The temperature of this tropical region is on average higher and more stable than that of temperate countries such as France, but the Tatamá National Park is very steep, allowing scientists to study insects at different altitudes (between 350 and 2 500 meters), the highest being the coolest.

For dragonflies and damselflies in these different areas, the authors determined the temperatures beyond which the insects flee the heat source, and those that prevent them from flying and hunting. “In order to collect this information, I spent many months scrambling up very steep and muddy slopes, crossing streams in search of dragonflies,” remembers Cornelio Bota-Sierra. “I sometimes came home completely rinsed, empty-handed.” This arduous and solitary work, carried out with a tiny budget, was nevertheless fruitful: as experiments show, dragonflies and damselflies never fly above 45°C, and all of them hide at 47°C, confirming their sensitivity to heat waves. . Insects in cool environments, at altitude and in forests, are nevertheless more sensitive to high heat than those in plains devoid of trees, indicating very pronounced local adaptations to climatic conditions. In addition, dragonflies tolerate high temperatures much better than damselflies. This is probably due to their elaborate circulatory system, which allows them to better dissipate scorching heat. In addition, the females continue to hunt under a blazing sun, perhaps to store reserves necessary for the production of eggs.

While the mathematical models intended to predict the future of insect populations are based on simple relationships between global warming and the presence of species in different areas, this work highlights the complexity of the responses of living organisms to global changes. As noted by Sylvain Pincebourde (CNRS) of the Insect Biology Research Institute “Beyond the reactions of insects to global warming, it is difficult to predict how their living environments in the plains, the mountains, under the trees, will themselves react to climate change.”

(1) Lire par exemple : Bernd Heinrich (1 979) Bumblebee Economics. Harvard University Press, Cambridge, MA.
(2) Damselflies are more slender than dragonflies, and their wings are folded at rest while those of dragonflies remain extended.
(3) Boot‐Saw , CA , Garcia‐Robledo , C. , Escobar , F. , Novelo‐Gutierrez , R. , & London , GA (2022). Environment, taxonomy and morphology constrain insect thermal physiology along tropical mountains. Functional Ecology36 (8), 1924-1935.

Source: Libération by www.liberation.fr.

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