Evidence for lower plasticity in CT_MAX at warmer developmental temperatures

Abstract

Understanding the capacity for different species to reduce their susceptibility to climate change via phenotypic plasticity is essential for accurately predicting species extinction risk. The climatic variability hypothesis suggests that spatial and temporal variation in climatic variables should select for more plastic phenotypes. However, empirical support for this hypothesis is limited. Here, we examine the capacity for ten Drosophila species to increase their critical thermal maxima (CT ) through developmental acclimation and/or adult heat hardening. Using four fluctuating developmental temperature regimes, ranging from 13 to 33 °C, we find that most species can increase their CT via developmental acclimation and adult hardening, but found no relationship between climatic variables and absolute measures of plasticity. However, when plasticity was dissected across developmental temperatures, a positive association between plasticity and one measure of climatic variability (temperature seasonality) was found when development took place between 26 and 28 °C, whereas a negative relationship was found when development took place between 20 and 23 °C. In addition, a decline in CT and egg-to-adult viability, a proxy for fitness, was observed in tropical species at the warmer developmental temperatures (26-28 °C); this suggests that tropical species may be at even greater risk from climate change than currently predicted. The combined effects of developmental acclimation and adult hardening on CT were small, contributing to a <0.60 °C shift in CT . Although small shifts in CT may increase population persistence in the shorter term, the degree to which they can contribute to meaningful responses in the long term is unclear.

Evolution and plasticity of thermal performance: an analysis of variation in thermal tolerance and fitness in 22Drosophilaspecies

“…Accordingly, we do not find any support suggesting that temperate species have higher plasticity than tropical species. Our finding of similar plasticity among species from the temperate and tropical origin is also consistent with earlier reports from Drosophila [34,37,55,56] and is emerging as a general pattern in ectothermic animals [35], although some have found a weak but positive association between plasticity and latitude in a large meta-analysis of ectotherms [36]. Thus, we conclude that our empirical findings offer no support for the idea that distance from the equator, degree of seasonality or thermal safety margin (calculated as the difference between upper thermal limit and maximum environmental temperature) correlate with the degree of plasticity, as has been suggested elsewhere [12,13,57].…”

Does social thermal regulation constrain individual thermal tolerance in an ant species?

“…Another important finding of our study is that workers from intermediate-elevation populations (1,000 and 1,300 m), who experienced the greatest temperature variability, displayed significantly greater thermal tolerance (had higher LT50 values) than workers from lower and higher elevation populations. These results support the CVH, which posits that exposure to greater temperature variability selects for greater thermal tolerance (Baudier, D'Amelio, Malhotra, O'Connor, & O'Donnell, 2018;Chan et al, 2016) or for more plastic phenotypes (Kellermann & Sgrò, 2018). Different recent studies have also found support for the CVH in a variety of organisms: tropical tadpoles (Gutiérrez-Pesquera et al, 2016); Andean frogs (Pintanel, Tejedo, Ron, Llorente, & Merino-Viteri, 2019); snails and vascular plants in the Caucasus (Mumladze, Asanidze, Walther, & Hausdorf, 2017); tropical aquatic insects (Shah et al, 2017); and tropical army ants (Baudier et al, 2018).…”

Insect responses to heat: physiological mechanisms, evolution and ecological implications in a warming world

“…Current evidence suggests that plastic responses of insects to heat are limited and may not be sufficient to withstand ongoing warming trends (Gunderson & Stillman, ; Kellermann & Sgrò, ). Furthermore, although important for rapid responses to sudden climate changes, plasticity has not yet been linked to sustained responses with fitness benefits across generations in insects (Kellermann & van Heerwaarden, ; Radchuk et al ., ).…”