Heatwaves and Novel Host Consumption Increase Overwinter Mortality of an Imperiled Wetland Butterfly

Abstract

Disruptive effects of climate change include range shifts, phenological mismatches among consumers and producers, and population declines. While these biological alterations have been widely documented, studies identifying specific mechanisms linking climate change to population declines are scarce. Extreme events, such as heatwaves can have devastating effects on living organisms and are increasing in frequency as Earth warms. Hence, understanding the effects of heatwaves on insects is necessary to inform conservation efforts and to develop predictions of population dynamics under future climate scenarios. Here, we experimentally evaluated the effects of heatwaves on the survival and phenology of the Baltimore Checkerspot (Euphydryas phaeton phaeton), a wetland butterfly with imperiled populations that has incorporated a novel host. We performed laboratory manipulations (implementing realistic temperature regimes) to assess the effect of heatwaves during summer and winter on the survival and phenology of E. p. phaeton. In addition, we analyzed historical temperature records to quantify the incidence of heatwaves within E. p. phaeton's range to assess their potential role in the decline of southeastern populations. We found that winter heatwaves with maximum temperatures of 20 • C can have more devastating effects on survival than summer heatwaves (up to 41 • C). Eggs endured acute heat stress during summer with no significant effects on phenology and survival; similarly, pre-overwintering larvae were robust to heatwave exposure, as only the most intense heatwave treatment reduced their survival (37% reduction compared to control conditions). By contrast, dormant larvae were the most vulnerable stage, as they lost from 2 to 6% of their body mass after a three-day summer heatwave. Furthermore, their exposure to winter heatwaves resulted in 75 to 100% mortality. Feeding on the native host provided higher resilience under thermal stress than feeding on the invasive, recently acquired host. Finally, both heatwave incidence and severity have increased in the southern range of E. p. phaeton in the period from 1894 to 2011. We show that warm winter days induced severe mortality, providing a mechanistic explanation of how climate change can trigger population declines in E. p. phaeton and other insects.

Further evidence for a global decline of the entomofauna

“…For example, winter heatwaves may have more devastating effects on the survival of the imperilled Baltimore checkerspot ( Euphydryas phaeton ) than summer heatwaves, since dormant larvae are the most vulnerable stage (Abarca et al . 2019). Also, the increasing frequency of drought periods and extreme weather events such as hurricanes and bushfires can cause catastrophic habitat destruction with concomitant losses of many animal species (Lister and Garcia 2018).…”

Climate change‐mediated temperature extremes and insects: From outbreaks to breakdowns

“…Although many studies show that exposure of eggs to TE can negatively affect larval growth, phenotypic plasticity in advanced larval stages can overcome the negative impacts of prior exposure to TE (Potter et al., 2011). In addition, TE exposure during earlier life stages does not always affect fitness in the adults (Abarca et al., 2019; Chen, Zhang et al., 2019; Potter et al., 2011; Zhang et al., 2015) and reduced fertility and fecundity following TE exposure of adults may be transient and disappear after several days (in males), or after re‐mating with unexposed males (in females; Dickinson, 2018; Sales et al., 2018). Given the short life cycles of most insects, under conditions of recurring or extended TE, many insects may not be able to recover even short periods of fertility loss.…”

Heat wave effects on the behavior and life-history traits of sedentary antlions

“…For instance, both subcontinental and marine heat waves have been shown to markedly alter the ecosystem structure, composition, and function ( Ruthrof et al 2018 ; Sanford et al 2019 ). On an organismal level, heat waves were demonstrated to induce the production of heat shock proteins ( Olabarria et al 2016 ) and change hematological parameters ( Pegado et al 2020 ), as well as negatively impact fitness-relevant traits, such as body condition and mortality ( Leung et al 2017 ; Abarca et al 2019 ) or sperm quality and function ( Hurley et al 2018 ; Sales et al 2018 ). However, the susceptibility of animals to all these effects largely depends on their immediate behavioral responses to heat waves, which ultimately dictate the extent to which essential traits, such as longevity or fertility are affected ( Huey et al 2012 ; Beever et al 2017 ).…”