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With temperature rises due to climate change, the wall brown butterfly is spreading into regions that were previously too cold. However, even rapid evolutionary adaptations are reaching their natural limits.
“As the Earth warms, many species are migrating to regions that were previously too cold but are now suitable habitats,” says evolutionary biologist Matthew Nielsen from the University of Bremen. A new study he published with colleagues from Stockholm University in the PNAS journal shows that in the case of the wall brown butterfly (Lasiommata megera), rapid evolutionary adaptations can support this process – “but only to a certain extent. Our findings show that although butterflies evolve as they spread northward, some barriers – such as cold winters – cannot be overcome so quickly.”
Field Experiments in Sweden
In field experiments, the scientists transferred butterflies from their populations in southern Sweden to locations both within and outside the current population range. Animals collected in the south (Skane County) and north (Södermanland and Uppland provinces) were released in outdoor enclosures in Skane, Södermanland, and southern Dalarna, the latter being an area not yet colonized by the wall brown butterfly. The aim of the study was to find out whether the butterflies had adapted evolutionarily to the new conditions through characteristics such as faster growth, adapted timing of hibernation, or increased cold resistance – traits that could enable them to survive in previously uninhabited habitats.
In fact, the butterflies from the north grew faster in the field cages – presumably an adaptation to the shorter summers at higher latitudes. They had also adapted the timing of their hibernation as caterpillars to the more northern conditions. It was striking that almost all animals – regardless of their origin – entered hibernation at the right time. This suggests a possible genetic stability or a pronounced plasticity of this trait. Nevertheless, almost no caterpillars survived the cold winters north of their current range. Winter mortality was high overall – and particularly drastic beyond the distribution range boundary.
Evolutionary Potential for Better Cold Adaptation Exhausted
“Understanding these limits is crucial for predicting where species – including pests and disease carriers – will move in the wake of climate change,” explains Nielsen. The researchers suspect that repeated natural selection due to harsh winter conditions may have already exhausted the evolutionary potential for better cold adaptation at the edge of the distribution range.
The results suggest that evolutionary changes can occur on timescales comparable to the speed of current climate change, but do not necessarily affect all traits that are critical for survival. For the wall brown, this means that further spreading will require milder winters. In order to reliably predict future changes in species distribution, it is necessary to know both the traits that change under new environmental conditions and those that define a species' ecological limit. Evolutionary biologist Nielsen: “As many species shift their range in response to global warming, this finding is crucial for better predicting future changes in biodiversity and the spread of species that could affect agriculture and human health.”
Prof. Dr. Matthew Nielsen, Insect Ecology in Changing Environments, University of Bremen, Phone: +49 421 218-50290, Email: nielsenm@uni-bremen.de
DOI:10.1073/pnas.2418392122
https://www.pnas.org/doi/10.1073/pnas.2418392122
In the fall, the caterpillars were raised in enclosures at the Tovetorp research station at Stockhol ...
Source: Mats Ittonen
Copyright: Mats Ittonen
The wall brown butterfly is common throughout much of Europe. In Sweden, it is often found on beache ...
Source: Mats Ittonen
Copyright: Mats Ittonen
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