A painted lady (Vanessa cardui), a species of butterfly common in urban habitats (Photo credit: Jean-Pol GRANDMONT)
The urban heat island effect is a well-known consequence of urbanization whereby temperatures in cities are higher than those in surrounding natural areas. One wrinkle in the heat island effect is that the increase in temperatures is not evenly distributed across time: city temperatures are proportionally higher in the evening and night due to the heat storage of buildings, pavement, and other urban structures. However, we do not yet have a clear understanding of how these changes in daily patterns of temperature affect organisms living in urban habitats.
Angie Lenard, a PhD student in Sarah Diamond’s lab at Case Western Reserve University is working to understand how higher nighttime temperatures in cities may affect invertebrates using caterpillars of the painted lady (Vanessa cardui), a butterfly found in cities around the world. Angie worked with Abe Perez, another graduate student in the Diamond lab, to expose caterpillars to 6 different temperature treatments. One of these treatments mimicked the normal daily fluctuations in temperatures that caterpillars might experience during summer, while two others included a hotter and cooler treatment, representing hot and cool summer days. Angie then created three paired treatments based on the same temperature regimes but which included enhanced nighttime temperatures, such as caterpillars living in the city might experience. The team then assessed the body mass and development rate of the caterpillars as they metamorphosed into adult butterflies.
Angie and her collaborators found that night-biased warming did have impacts on growth and development, but that these changes were idiosyncratic and varied with the life stage of the individuals. For instance, warming treatments caused increases in development, but both increases and decreases in body size, which was surprising. Angie will be digging into these topics more, examining whether there are sex-specific effects at play and whether caterpillars from natural habitats and the lab might respond differently to these temperatures. Stay up-to-date with Angie’s work by following her on Twitter: @angie_lenardski
Urban nighttime-biased warming alters growth and developmental trajectories throughout ontogeny in a cosmopolitan butterfly species LENARD, A; PEREZ, A; DIAMOND, SE; Case Western Reserve University
Leave a Reply