Some like it hot: the effects of climate change on reproduction, immune function and disease resistance in the cricket Gryllus texensis

In many parts of the world, climate change is increasing the frequency and severity of heat waves. How do heat waves impact short-lived poikilotherms such as insects? In the cricket, Gryllus texensis, 6. days of elevated temperatures (i.e. 7 degrees C above the average field temperature and 5 degrees C above their preferred temperature) resulted in increased egg laying, faster egg development and greater mass gain. The increased temperature also increased activity of phenoloxidase and lysozyme-like enzymes, two immune-related enzymes, and enhanced resistance to the Gram-negative bacterium Serratia marcescens. When given a sublethal S. marcescens infection, G. texensis maintained increased reproductive output at the elevated temperature (33 degrees C). These data suggest that heat waves could result in more numerous, disease resistant, crickets. However, resistance to the Gram-positive bacterium, Bacillus cereus was lower at temperatures above or below the average field temperature (26 degrees C). A sublethal infection with B. cereus reduced egg laying at all temperatures and suppressed the increase in egg laying induced by higher temperatures. These results suggest that for some species-pathogen interactions, increased temperatures can induce trade-offs between reproduction and disease resistance. This result may partly explain why G. texensis prefers temperatures lower than those that produce maximal reproductive output and enhanced immune function.