New research by University of Western Ontario PhD student Caroline Williams suggests that the effect of climate change may vary between different species, even among those that are closely related, such as two specific species of butterfly.
That’s all the more important when exploring an extremely complex process like poleward range expansion (migration north and south) and may prove vital to the very survival of our winged friends.
In a study to be published this week in the Journal Proceedings of the National Academy of Sciences and led by Jessica Hellmann and Shannon Pelini at the University of Notre Dame, Williams and her advisor, Brent Sinclair, Williams examined the effects of warming on two butterfly species from the West Coast of North America – the Propertius Duskywing and the Anise Swallowtail. These two species differ in body size, preferences for food and dispersal ability.
The Notre Dame researchers swapped caterpillars of both species between the centre of their range (southwestern Oregon) and the northern limits of where the species live (Vancouver Island, British Columbia). In both the field and the laboratory, such experiments test the effects of temperature change during development on butterfly growth and survival.
Caterpillars of the Propertius Duskywing grew and survived better over summer in the warmer conditions, which alone suggests that populations near the northern limit could increase under climate change, a helpful precursor for expanding to new locations further to the north.
Using high-precision equipment funded by the Canada Foundation for Innovation, Williams measured the energy use of Propertius Duskywing caterpillars during the winter and found that warmer conditions were actually disadvantageous to caterpillars that live at the range edge, causing them to burn through more of their limited energy stores. These energy losses under warmer winter temperatures could undo summer gains and prevent population increases, just when northern populations need to grow to track changing climatic conditions.
In the same experiment, larvae and pupae of the Anise Swallowtail had slower growth and lower survival in warmer summer conditions, and also burned far more energy than usual during the simulated warmer winter.
“These animals can’t get any more fuel once they enter their overwintering state. It’s like a car with a limited gas tank – and no fuel stops all winter,” explains Williams.
“One important aspect of this study is that it shows that the impacts on the butterflies depend on where they came from. If they come from somewhere that is already warm, they can deal with warm winters. If they don’t, they burn too much fuel,” says Sinclair, an Assistant Professor in the Department of Biology at Western.