Meeting Abstract
It is well established that mean temperatures are rising; however, rates of warming are not equal spatially or temporally. Cities create “urban heat islands” and the pattern of diel warming is often asymmetrical. Rises in nighttime temperatures contribute more to mean temperature change than rises in daytime temperatures. However, the biological consequences of such nighttime-biased warming are largely unknown. In this study, we examined how nighttime-biased warming affects the growth and development of painted lady caterpillars (Vanessa cardui), a widespread butterfly species, throughout ontogeny. We reared animals under one of six diurnally fluctuating temperature treatments: three treatments represented typical diurnal fluctuations in summer temperatures, including an average day, a warm day, and a cool day; the three remaining treatments modified these diurnal fluctuations such that the warming was biased towards the nighttime, but with comparable daytime temperatures. We also compared the effects of these fluctuating temperature treatments against chronic warming treatments with the same mean temperature. We recorded the body mass of caterpillars at each larval instar, at metamorphosis (pupation), and upon eclosion as adults, and we recorded the development time (in days) to each developmental stage. Our results indicate consistent acceleration of development time under nighttime-biased warming regimes; however, the effect of nighttime-biased warming on body mass throughout ontogeny was more idiosyncratic.
