Evolution under fluctuating conditions and exposure to heatwaves in the seed beetle, Callosobruchus maculatus

Edward Richard Ivimey-Cook , Sarah Glavan, Sophie Bricout, Claudio Piani, Elena C Berg

Heatwaves, temporary periods of elevated temperatures, are increasing both in magnitude and in frequency and have been shown to have devastating negative effects on a wide range of taxa. However, to date, most studies investigating the impacts of heatwaves have either focus on populations that have evolved under constant conditions prior to assaying or, more importantly, only investigated the short-term outcomes of periods of elevated temperatures. Here, using the seed beetle, Callosobruchus maculatus, we investigate both the short- and long-term effects of evolution after 43 generations of fluctuating temperature with added heatwave exposure (a +2C increase in diurnal temperature peaking at 42C) on two important life history traits, development time and lifetime reproductive success (LRS). We found that when individuals were assayed under fluctuating conditions, those that evolved under heatwave conditions developed at a similar rate but had reduced LRS than those evolved and assayed under the same fluctuating conditions. In contrast, when individuals were assayed under a novel benign temperature of 29C, both thermal regimes developed slower and had a similar LRS that was significantly greater than the number produced when treatments were assayed in the stressful fluctuating environment. All together, this suggests that long-term evolution under periods of elevated temperatures may lead to increased resilience both in the long-term with exposure to repeated heatwaves, but also in the short-term when individuals are exposure to rapid environmental change. This study further underscores the importance of using natural diel fluctuations to enhance our understanding of organisms’ responses to climate change. Additionally, it emphasises the potency of investigating long-term multigenerational exposure to heatwaves.