The Heat Shock Response Under Natural Conditions in Two Paper Wasp Species

In a warming world, mechanisms, such as the heat shock response, which plays a role in the recovery from or tolerance towards heat stress, are of increasing importance. Certain heat shock protein genes (<i>hsps</i>) have previously been shown to be highly inducible in several paper wasp species during high temperature stress under laboratory conditions. Here, we sought to investigate how <i>hsps</i> are expressed under natural daily temperature fluctuations by collecting broods from wild nests of two species of paper wasps (<i>Polistes dominula</i>, <i>P. nimpha</i>). We collected them at 06:00 and 16:00, the expected low and high points in daily <i>hsp</i> expression, and measured the expression of three <i>hsps</i> (<i>hsp70</i>, <i>hsp83</i>, <i>hsc70</i>). We found that the nest temperature in July could reach temperatures that result in a large upregulation of <i>hsp</i> expression in the laboratory. Under natural conditions, however, we found that the induction response was much more moderate and limited to the larvae. The pupae showed no response to the daily fluctuating temperature and had a constant expression similar to that of larvae in the afternoon. The similarities and differences between natural and laboratory <i>hsp</i> expressions highlight the importance of field studies, as they add valuable context when interpreting laboratory results.