Laboratory experiments using the Green-veined White butterfly and the Latticed Heath moth, from Stockholm, Helsinki and surrounding rural areas confirm that the urban populations of both species have evolved different responses to day length compared to neighboring rural populations.

Grass and a couple of white flowers with white butterflies
The study carried out experiments with the Green-veined White butterfly in the major cities of Stockholm and Helsinki. Photo: Christer Wiklund


“Our results provide evidence for adaptation to the longer growing season created in cities by urban warming and show that that at least some urban populations of butterflies and moths appear to have adapted to distinct climate typical of large cities like Stockholm and Helsinki”, says Matthew Nielsen who is a Postdoctoral researcher at the Department of Zoology at Stockholm University and one of the lead authors of the study “Urbanization extends flight phenology and leads to local adaptation of seasonal plasticity in Lepidoptera” published in the scientific journal PNAS.

The study, performed by researchers at Stockholm University, University of Oulu, Lund University, the Finnish Environment Institute and the Natural Resources Institute in Finland, suggests that the altered seasonality in urban environments is an important cause of evolution in urban populations. It is thus likely that urban adaptations in seasonal responses have evolved in many species that manage to live in urban environments.

“It is fascinating that earlier studies of evolutionary consequences of climate change have identified very similar changes in these same traits. Urban environments seem to be another example of humans creating similar selection on insect populations”, says Associate Professor Karl Gotthard, also at the Department of Zoology at Stockholm University and a coauthor of the study.

Cities tend to be warmer than surrounding rural areas, which lengthens the growing season in urban environments. Many insects can take advantage of longer growing seasons by producing extra generations, but they rely on day length to determine the time to pause their life cycle for winter (a state called diapause). Thus, urban environments potentially promote the evolution of novel seasonal adaptations in insects.

“Our analysis of long-term observational data from multiple cities in Sweden and Finland also support to the idea that diapause starts later in the year in urban than in rural populations, and it shows the great value of long-term monitoring programs, such as the Swedish and Finnish Butterfly monitoring schemes, as well as citizen science for understanding and analyzing evolutionary processes”, says Matthew Nielsen.

Latticed Heath moth
The other species studied was the Latticed Heath moth. Photo: Sami Kivelä

This article was originally published on the Department of Zoology’s website.

Link to the original research article: