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Warmer autumns reduce the life expectancy of butterflies

A new study led by Stockholm University has found that longer and warmer autumns make it less likely that green-veined white butterflies – a species common throughout Europe and the United Kingdom – will survive winter. Although the butterflies exposed to warmer conditions did not die immediately, those that experienced them were less likely to survive to adulthood the following spring.

“Climate change is making autumns warmer and last longer, and it was this specific combination of conditions that had the greatest impact on the butterflies in our study,” said study lead author Dr. Matthew Nielsen, a postdoctoral researcher at Stockholm University. “We show that stressful conditions experienced at one time of year can have lasting negative consequences at other times of year, linking changes in one season to consequences in others.”

According to Dr. Nielsen, animals which enter a dormant stage through the winter are particularly vulnerable to increasing temperatures because this raises their metabolic rates, making them run out of energy faster. “Even though dormant animals use less energy than active animals, they use more when it’s warmer, and they can’t eat to replace that lost energy. It is already established that warmer winters are actually worse for dormant animals than colder ones, and our findings show that warmer autumns are potentially even more dangerous,” he said.

In laboratory conditions, the scientists exposed the chrysalises of butterflies to simulated autumn conditions of varying temperature and length and found that those exposed to warmer and longer conditions lost significantly more weight and used more energy than those exposed to milder conditions.

Since the study was performed in the lab, it may be difficult to extrapolate these findings to populations in the wild that are exposed to natural seasonal and daily variations. However, according to the researchers, such variations could in fact further intensify the metabolic costs of autumn conditions.

The scientists are now expanding their research to explore the effects of climate change on butterflies in more detail and assess the effects of different seasons. “In our study we only considered survival to adulthood, but there could be even more negative effects later in life, for example on the ability to find mates or the number of eggs laid. Studying how warming in autumn, winter, and spring interact will also be key to understanding the actual impacts of climate change on dormant animals,” Dr. Nielsen concluded. 

The study is published in the journal Functional Ecology.

By Andrei Ionescu, Staff Writer

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