Daily temperature extremes play an important role in predicting thermal effects

Abstract

Organisms in natural environments experience diel temperature fluctuations, including sporadic extreme conditions, rather than constant temperatures. Studies based mainly on model organisms have tended to focus on responses to average temperatures or shortterm heat stress, which overlooks the potential impact of daily fluctuations, including stressful daytime periods and milder nighttime periods. Here, we focus on daily maximum temperatures, while holding night-time temperatures constant, to specifically investigate the effects of high temperature on demographic parameters and fitness in the English grain aphid Sitobion avenae. We then compared the observed effects of different daily maximum temperatures with predictions from constant temperature-performance expectations. Moderate daily maximum temperatures depressed aphid performance while extreme conditions had dramatic effects, even when mean temperatures were below the critical maximum. Predictions based on daily average temperature underestimated negative effects of temperature on performance by ignoring daily maximum temperature, while predictions based on daytime maximum temperatures overestimated detrimental impacts by ignoring recovery under mild night-time temperatures. Our findings suggest that daily maximum temperature will play an important role in regulating natural population dynamics and should be considered in predictions. These findings have implications for natural population dynamics, particularly when considering the expected increase in extreme temperature events under climate change.

Effects of Thermal Regimes, Starvation and Age on Heat Tolerance of the Parthenium Beetle Zygogramma bicolorata (Coleoptera: Chrysomelidae) following Dynamic and Static Protocols

“…bicolorata used for the trials was kept under fluctuating thermal conditions for many generations, it is also possible that transmissible trans-generational effects (see discussions in Sgrò et al ., 2016) [29] favored performance and plasticity under fluctuating thermal regimes. Thus, these findings may indicate an important role of diel thermal fluctuations for signaling risk of future stressful events in insects [76]. This, however, does not incontrovertibly discredit the use of constant acclimation temperatures which have been shown to improve performance even under field conditions [15,17].…”

“…However, it should be noted that the target traits being compared also differed, being survival after exposure to a heat spell or the ability to move at increasing temperatures. These findings may suggest that immediate exposure to stressfully high (constant) temperatures potentially overestimates thermal tolerance and other temperature-related fitness parameters [70,76,78]. Alternatively, hardening may only affect heat survival but not proxies thereof.…”

Stage-specific heat effects: timing and duration of heat waves alter demographic rates of a global insect pest

“…Consequently, these temperature variations shift the performances of ectotherms in constant environments (Raffel et al 2013;Vasseur et al 2014;Colinet et al 2015). The life performances under constant hot conditions may be weakened by the nighttime recovery (Xing et al 2014;Zhao et al 2014) or exacerbated by daytime temperature extremes (Welbergen et al 2008;Ma et al 2015a). In addition, ectotherms may also be able to buffer the detrimental impacts of high temperatures through behavioral thermoregulation (Kearney et al 2009;Ma and Ma 2012a, b).…”

Timing of stressors alters interactive effects on a coastal foundation species

“…, Ma et al. ). In particular, extreme events can influence ecological dynamics more than the mean level of a given factor (Gaines and Denny , Easterling et al.…”

“…Stressor timing can vary in several key ways, including fluctuations in individual stressors over time. Many studies have focused on changes in mean climate conditions (Easterling et al 2000, Smith 2011), but fluctuations around mean conditions can profoundly influence how organisms respond to stressors (Lawson et al 2015, Ma et al 2015. In particular, extreme events can influence ecological dynamics more than the mean level of a given factor (Gaines and Denny 1993, Easterling et al 2000) and can play a critical role in biotic responses to climatic shifts (Stenseth et al 2002, Helmuth et al 2006, Zimmermann et al 2009).…”