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Hotter climates causing male dragonflies to lose wing colour: Study

The authors estimate that male wing ornamentation will decline by 2070, but very modestly. Female wings will not show much difference.

Written by Ritvik Chaturvedi | Bengaluru |
November 26, 2021 8:26:15 pm
Common_whitetailWarmer climates favour lighter colours on wing ornamentation. (Wikimedia Commons)

Wings of male and female dragonflies adapt differently to warming climates, a recent study led by researchers from Washington University has found.

The team examined wing ornamentation, colouration and production of melanin in order to assess how individuals had adapted to various climatic requirements and how it offered them an advantage in the mating game.

While the evolution of physiological characteristics, like reproductive cycle and body sizes, have been considered as possible ways a species can adapt to its climate; mate choice has seldom been looked at as a driving force in evolution. Mate choice, however, is a significant way in which selection operates and improves the fitness of the species from one generation to the next.

Dragonflies and their close relatives, the damselflies have for long been used as model organisms in ecological studies. This is due to their short life history and the relative ease with which they can be bred and cared for in the laboratory.

The team found that warmer climates favour lighter colours on wing ornamentation because of obvious reasons: dark wing colours absorb solar radiation that leads to heating.

Both male and female dragonflies and damselflies use wing ornamentation as cues for mating, trying to attract more mates and ward off rivals and competitors.

While males with greater wing melanisation have been observed to typically attract more females, wing melanisation comes at a certain cost. It can damage wing tissues, reduce the male fighting ability and could even be fatal if it is unusually warm.

An important finding of the study was that although males in warmer ranges have less wing melanisation than those in cooler ranges, no such perceptible difference in melanisation was found for females. Neither is there a relationship between the temperature of a species’ range and the extent of female wing melanisation.

There are a few reasons for this. The current geographic distribution of many of these dragonfly lineages does not reveal how old these species/populations are very accurately.

After the ice sheets retreated following the Last Glacial Maxima ( about 11,000 years ago), dragonfly populations colonised many areas where melanisation was not very costly. This is a phenomenon known as ‘ecological filtering.’

Also, ornamentation is quite ‘evolutionary labile,’ which means it can respond fairly quickly to local climates and is even adjusted over the course of one individual’s lifetime. Indeed, when wing ornamentation of dragonfly populations in different geographical zones, separated for nearly 100 million years, were examined, they revealed the same patterns: male dragonflies in warmer climes had lighter wings than their counterparts in cooler climes, and no such difference was found among female conspecifics.

Similar results were obtained when the study sampled ten widely distributed dragonfly species – the years that were warmer-than-average exhibited less wing melanisation in males and not females.

The authors estimate that male wing melanisation/ornamentation will decline by 2070, but very modestly. Female wing melanisation will not show much difference.

“In particular, female ornaments show no consistent relationship with climatic conditions within or among species, suggesting that ornaments have different thermal consequences for males and females,’ says the study. This is largely due to the typically cooler microhabitats that females inhabit by and large.

That organisms evolve to changing climates is no news, and was something known to evolutionary biologists (Charles Darwin and Alfred Russell Wallace) as early as the nineteenth century. However, the study is notable in that it assesses whether or not climatic adaptations lead to tweaking traits that are often used in mating and reproduction.

“Rapid changes in mating-related traits might hinder a species’ ability to identify the correct mate. Even though our research suggests these changes in pigmentation seem likely to happen as the world warms, the consequences are something we still really don’t know all that much about yet,” lead author Michael Moore said in a release.

– The author is a freelance science communicator. (mail[at]ritvikc[dot]com)

 

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