By evolving to use only widespread wild Geranium food plants, the brown argus butterfly has been able to spread rapidly north in the UK in response to recent climate change.  However, the evolution of a more specialised diet may limit this butterfly’s continued spread north, into areas where food plants other than Geranium are common.

Dr James Buckley and Dr Jon Bridle, the authors of the study published in Ecology Letters, explain that: "Our research on the brown argus butterfly shows that rapid evolutionary change in a species’ diet is important for responding to recent climate change. Adaptations like this that alter how species interact may be crucial for many other organisms to survive in a changing world.”

However, the researchers emphasise that although rapid evolutionary responses can allow rapid colonisation of new areas, they may result in the loss of variation in ecologically important traits, such as dietary preferences. Such loss of variation could compromise the ability of species to adapt to future climate change.

In addition, unlike the brown argus, many butterflies already have restricted diets. This means they may be unable to rapidly adapt to climate change and be condemned to extinction in increasingly fragmented habitat.

The researchers used shopping baskets as cages to transplant female butterflies between habitats across the species' UK distribution, and counted the number of eggs they laid on larval food plants in different areas.

Butterflies from long-established southern sites laid eggs on two food plants: the locally common rockrose and wild Geranium.  By contrast, females from recently colonised populations further north will only lay eggs on the widespread Geranium and not rockrose.  These results show the importance of conducting experiments in natural habitats as well as in laboratory environments to identify how organisms will adapt to ongoing climate change.

Paper

'Loss of adaptive variation during evolutionary responses to climate change' by James Buckley and Jon R. Bridle in Ecology Letters