Plasticity of upper thermal limits to acute and chronic temperature variation in Manduca sexta larvae

Abstract

In many ectotherms, exposure to high temperatures can improve subsequent tolerance to higher temperatures. However, the differential effects of single, repeated or continuous exposure to high temperatures are less clear. We measured the effects of single heat shocks and of diurnally fluctuating or constant rearing temperatures on the critical thermal maximum (CT max ) for final instar larvae of Manduca sexta. Brief (2 h) heat shocks at temperatures of 35°C and above significantly increased CT max relative to control temperatures (25°C). Increasing mean temperatures (from 25 to 30°C) or greater diurnal fluctuations (from constant to ±10°C) during larval development also significantly increased CT max . Combining these data showed that repeated or continuous temperature exposure during development improved heat tolerance beyond the effects of a single exposure to the same maximum temperature. These results suggest that both acute and chronic temperature exposure can result in adaptive plasticity of upper thermal limits.

Evidence for lower plasticity in CTMAX at warmer developmental temperatures

“…For instance, in lizards heat hardening can increase CT MAX by 2.6°C, although trade-offs with basal CT MAX is suggestive of an upper limit to hardening responses (Phillips et al, 2016). In addition, developmental acclimation and hardening can also increase CT MAX in the copepod Tigriopus californicus, the springtail Orchesella cincta and the moth Manduca sexta by 1.3°C,~1.5°C and~1.2°C, respectively (Kingsolver et al, 2016;Alemu et al, 2017;Pereira et al, 2017). It is possible that more extreme temperatures, Table 2 Phylogenetic least squares analysis examining the relationship between CT MAX and acclimation response ratio (ARR) and environmental variables.…”

Quantifying thermal extremes and biological variation to predict evolutionary responses to changing climate

“…As an example, the TPCs for larval growth rates in Manduca sexta measured over short (24 h) or long (duration of larval growth period, 15-50 days) time scales differ in optimal temperature, thermal . Similarly, thermal thresholds of larval M. sexta are much higher at shorter than at longer time scales: the mean upper thermal limit for survival (through the larval period) is 35-368C, whereas mean CT max and upper lethal limits are 44-468C [34].…”

“…For example, the stressful impacts of heat waves are often determined by repeated exposures to high daily maximum temperatures rather than to overall mean temperatures. In addition, the biological effects of single versus repeated exposures to extreme temperatures can be qualitatively different [33][34][35][36][37][38]. To explore this issue, we average daily maximum temperatures for two North American sites across weeks (moving average), months and years.…”

Variation in developmental temperature alters adulthood plasticity of thermal tolerance inTigriopus californicus

“…For instance, adult plasticity of swimming performance and metabolic rate depends on developmental environment in mosquitofish (Gambusia holbrooki; Seebacher et al, 2014;Seebacher and Grigaltchik, 2015). Yet, despite the likely biogeographic importance of thermal tolerance limits (Sunday et al, 2012), and many published examples of thermal tolerance limit plasticity in ectothermic organisms as a result of developmental or adulthood temperatures (e.g., Stillman and Somero, 2000;Ford and Beitinger, 2005;Fangue et al, 2006;Angiletta, 2009;Overgaard et al, 2011;Cooper et al, 2012;Tepolt and Somero, 2014;Jakobs et al, 2015;Troia et al, 2015;Kingsolver et al, 2016;Pereira et al, 2017;Diamond et al, 2018;Yanar et al, 2019), relatively few studies have assessed the potential for developmental temperatures to shape the phenotypic plasticity of upper thermal tolerance in adults (although see Schaefer and Ryan, 2006;Kellermann et al, 2017;Kellermann and Sgrò, 2018). Here we examine these effects, and their potential mechanistic basis in populations of the intertidal copepod Tigriopus californicus.…”