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Ethology

Wings of strife

Male damselflies measure their own strength and that of their opponents in determining confrontation strategy

Intensity and size of red spot are critical factors in competition

Stanislav GorbIntensity and size of red spot are critical factors in competitionStanislav Gorb

By the water of a sunny brook in some areas of the Brazilian Cerrado, we may see red damselflies flitting around each other. They are males of Mnesarete pudica, either showing off to females perched on branches or leaves of grass or competing against other males to ensure a suitable territory where their mates can lay their eggs. Scientists already knew that appearance — namely, pigmentation intensity and size of the red spot on the wing — was the key to success, but biologist Rhainer Guillermo-Ferreira decided to investigate how this works, as part of his doctoral research at the University of São Paulo campus in the city of Ribeirão Preto, advised by Pitágoras Bispo at São Paulo State University (Unesp), in collaboration with the group headed by Stanislav Gorb at the University of Kiel, in Germany. “Our question was: are they able to see this and make an assessment?” says Guillermo-Ferreira. The answer is yes, according to his paper published in March 2015 on the website of the journal The Science of Nature.

In the study, Guillermo-Ferreira observed male-male contests in a natural scenario and also made detailed analyses of wing pigmentation. As he analyzed the confrontations between rival males with differing degrees of quality disparity, as measured by the amount of red pigment in the wings and by body size, the researcher was surprised to discover that male damselflies of this species not only assess the attributes of their opponents, but also assess their own attributes, and take both into account when making decisions. “We saw variations in confrontation strategy according to this assessment,” explains the biologist, now a professor at the Federal University of Greater Dourados, in the state of Mato Grosso do Sul.

According to Guillermo-Ferreira, weak males do not take chances on prolonged sessions of vigorous flight, which are used as demonstrations of strength. Instead, they move straight to aggression. Strong males, on the other hand, ponder the situation more carefully. When facing a visibly weak opponent, they respond by chasing him and making direct threats. If their rivals are more evenly matched, strong males launch into flight demonstrations that require a higher energy expenditure. These contests can go on for hours, until one of the competitors gives up. The researchers captured some of the males and painted their wings with a felt-tip marker, to enhance both the intensity and size of the red spot. As a result, these damselflies were deemed stronger by their adversaries, changing their confrontation strategy.

Coloring the wings of insects and observing their exhibitions may seem more child’s play than science, but this is definitely not the case. Guillermo-Ferreira’s experiments have opened a window into intriguing aspects that might also apply to other species. “The behavior shown by these damselflies reveals that animals with simple brains can use complex decision-making systems,” he concludes.

Project
Ephemeroptera, Plecoptera and Trichoptera (Insecta): reducing Linnean, Wallacean and Henningian deficits (No. 2012/21196-8); Grant mechanism Regular Research Grants; Principal investigator Pitágoras da Conceição Bispo (Unesp); Investment R$309,297.74 (FAPESP).

Scientific article
GUILLERMO-FERREIRA et al. Variable assessment of wing colouration in aerial contests of the red-winged damselfly Mnesarete pudica (Zygoptera, Calopterygidae). The Science of Nature. V. 102. Mar. 2015.

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