Induced thermotolerance and associated expression of the heat‐shock protein Hsp70 in adult Drosophila melanogaster

Abstract

1. Inducible heat‐shock proteins are synthesized when temperatures are increased to levels substantially above normal. The functional role of these proteins is well known at the cellular level. Today increasing interest has been directed towards the importance of heat‐shock proteins for resistance of whole organisms to high‐temperature stress and other environmental stressors. 2. Here the functional relationship between the heat‐shock protein, Hsp70, and thermal resistance in adult Drosophila melanogaster was examined by comparing thermal resistance, i.e. survival at 39 °C for 85 min, and levels of Hsp70 at various times elapsed (2, 4, 8, 16, 32 and 64 h) after thermotolerance was induced by short‐term acclimation/heat hardening at 37 °C for 55 min. 3. Levels of Hsp70 in both males and females were highest 2 h after heat hardening and declined with longer times elapsed. The rate of decrease initially was very fast but diminished with increasing time. After 32 h the level of Hsp70 approached the level in flies that were not hardened. Levels of Hsp70 in males exceeded that of females during the entire period. 4. Survival of both sexes increased with increasing time after heat hardening and reached an optimum between 8 and 32 h. Thereafter resistance decreased with longer times elapsed. Survival of females generally exceeded that of males except after 16 and 64 h. 5. Regression analysis applied to the data on Hsp70 levels revealed that the model describing these data could not explain the data for survival. Also, higher levels of Hsp70 in males compared with females were not associated with greater survival in males. However, statistical analysis on paired measurements of Hsp70 and survival revealed a positive association between Hsp70 level and survival at each time elapsed after induction of thermotolerance.

Inbreeding interferes with the heat-shock response

“…Several studies have found a positive correlation between heat tolerance and HSP70 expression (Bahrndorff et al, 2009), whereas others have shown opposite or no correlations (Dahlgaard et al, 1998;Bahrndorff et al, 2009Bahrndorff et al, , 2010. Using the same treatments as herein a previous study on B. anynana, we showed that exposure for 2 h to 39 1C strongly increased subsequent heat-stress survival (Franke and Fischer, 2013), suggesting that a positive relationship between HSP70 expression and heat tolerance exists also in our study organism.…”

Role of sequential low-tide-period conditions on the thermal physiology of summer and winter laboratory-acclimated fingered limpets, Lottia digitalis

“…This is in contrast to a previous study on a mid-intertidal limpet, Cellana toreuma, that found no Hsp70 response to aerial exposure alone at 20 °C (Huang et al 2015). Although there is an accumulating body of evidence that suggests that the heat-shock response and the induction of Hsps is a primary cellular mechanism underlying heat hardening (Kregel 2002;Sørensen et al 2003), several studies have found that heat hardening may be uncoupled with Hsp synthesis and concentrations (Easton et al 1987;Dahlgaard et al 1998). In the current study, Ub-conjugated proteins were measured directly as a measure of protein damage present in the limpets prior to exposure to the lethal temperature increase.…”

Phenotypic diversity, population structure and stress protein-based capacitoring in populations of Xeropicta derbentina, a heat-tolerant land snail species

“…The structure of Hsp70 is phylogenetically highly conserved, even though the capacities for its induction may vary considerably among populations of the same species (Köhler et al 2000). Differences in Hsp70 levels can directly account for stress tolerance (Köhler et al 1992;Dahlgaard et al 1998;Feder and Hofmann 1999;Köhler et al 2000), which often is influenced by microgeographical selection processes. Since the production of stress proteins, however, is energy consuming, it is reasonable to assume that Hsp induction trades off against other fitness parameters because of constraints in energy allocation (Krebs and Loeschcke 1994;Silbermann and Tatar 2000;Kristensen et al 2008).…”