Rapid thermal responses and thermal tolerance in adult codling moth Cydia pomonella (Lepidoptera: Tortricidae)

SUMMARYEcological relevance and repeatability of results obtained in different laboratories are key issues when assessing thermal tolerance of ectotherms. Traditionally, assays have used acute exposures to extreme temperatures. The outcomes of ecologically more relevant ramping experiments, however, are dependent on the rate of temperature change leading to uncertainty of the causal factor for loss of function. Here, we test the physiological consequences of exposing female Drosophila melanogaster to gradually increasing temperatures in so-called ramping assays. We exposed flies to ramping at rates of 0.06 and 0.1°Cmin -1 , respectively. Flies were sampled from the two treatments at 28, 30, 32, 34, 36 and 38°C and tested for heat tolerance and expression levels of the heat shock genes hsp23 and hsp70, as well as Hsp70 protein. Heat shock genes were upregulated more with a slow compared with a faster ramping rate, and heat knock-down tolerance was higher in flies exposed to the faster rate. The fact that slow ramping induces a stronger stress response (Hsp expression) compared with faster ramping suggests that slow ramping induces more heat damage at the cellular level due to longer exposure time. This is supported by the observation that fast ramped flies have higher heat knock-down tolerance. Thus we observed both accumulation of thermal damage at the molecular level and heat hardening at the phenotypic level as a consequence of heat exposure. The balance between these processes is dependent on ramping rate leading to the observed variation in thermal tolerance when using different rates.

Section: Discussionmentioning

confidence: 99%

Cellular damage as induced by high temperature is dependent on rate of temperature change – investigating consequences of ramping rates on molecular and organismal phenotypes in Drosophila melanogaster Meigen 1830

Sørensen

Loeschcke

Kristensen

2012

“…Indeed, routinely used rates in the laboratory are among the fastest small ectotherms would likely ever encounter and a rate of 1°Cmin -1 is far beyond what might be expected (Fig.1), except perhaps in highly unusual situations, such as during the passage of extreme weather fronts. In other words, lower rates are more likely to reflect the situation in the field except perhaps during rare, extreme conditions (see also Sinclair, 2001), and for thermal maxima the typical finding is that lower rates of warming result in lower values of the CT max or upper thermal limits (Terblanche et al, 2007a;Chown et al, 2009;Mitchell and Hoffmann, 2010) (but see Chidawanyika and Terblanche, 2011). At the limit, work on long-lived Antarctic marine species is showing that rates of change in the order of 1°C per month result in estimates of upper thermal limits of ca.…”

Section: The Environmental Contextmentioning

confidence: 99%

Ecologically relevant measures of tolerance to potentially lethal temperatures

Terblanche

Hoffmann

Mitchell

et al. 2011

Self Cite

389

370

SummaryThe acute thermal tolerance of ectotherms has been measured in a variety of ways; these include assays where organisms are shifted abruptly to stressful temperatures and assays where organisms experience temperatures that are ramped more slowly to stressful levels. Ramping assays are thought to be more relevant to natural conditions where sudden abrupt shifts are unlikely to occur often, but it has been argued that thermal limits established under ramping conditions are underestimates of true thermal limits because stresses due to starvation and/or desiccation can arise under ramping. These confounding effects might also impact the variance and heritability of thermal tolerance. We argue here that ramping assays are useful in capturing aspects of ecological relevance even though there is potential for confounding effects of other stresses that can also influence thermal limits in nature. Moreover, we show that the levels of desiccation and starvation experienced by ectotherms in ramping assays will often be minor unless the assays involve small animals and last for many hours. Empirical data illustrate that the combined effects of food and humidity on thermal limits under ramping and sudden shifts to stressful conditions are unpredictable; in Drosophila melanogaster the presence of food decreased rather than increased thermal limits, whereas in Ceratitis capitata they had little impact. The literature provides examples where thermal limits are increased under ramping presumably because of the potential for physiological changes leading to acclimation. It is unclear whether heritabilities and population differentiation will necessarily be lower under ramping because of confounding effects. Although it is important to clearly define experimental methods, particularly when undertaking comparative assessments, and to understand potential confounding effects, thermotolerance assays based on ramping remain an important tool for understanding and predicting species responses to environmental change. An important area for further development is to identify the impact of rates of temperature change under field and laboratory conditions.

“…As a consequence, temperate organisms are expected to increase in abundance under climate change because fecundity and developmental rate are often enhanced by a small increase in mean temperature (Cannon, 1998;Parmesan and Yohe, 2003;Rall et al, 2010). However, previous studies on the impact of short-term heat stress (for several hours at constant high temperatures) show that temperate organisms are particularly vulnerable to extreme high temperatures (Tomanek, 2005;Huang et al, 2007) and predict a substantial decrease in these populations (Terblanche et al, 2008;Chidawanyika and Terblanche, 2011;Zizzari and Ellers, 2011). However, our results show that ecologically relevant daily maximum temperatures have an intermediate impact, in contrast to model predictions based on either mean daily temperatures or mean daylight temperatures.…”

Section: Population Predictions and Climate Changementioning

confidence: 99%

Daily temperature extremes play an important role in predicting thermal effects

Hoffmann

2015

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.