A simulated natural heatwave perturbs bumble bee immunity and resistance to infection

As a consequence of ongoing climate change, heatwaves are predicted to increase in frequency, intensity, and duration in many regions. Such extreme events can shift organisms from thermal optima for physiology and behavior, with the thermal stress hypothesis predicting reduced performance at temperatures where the maintenance of biological functions is energetically costly. Performance includes the ability to resist biotic stressors, such as infectious diseases. Climate change is a proposed threat to native bee pollinators, directly and through indirect effects on floral resources, but the thermal stress hypothesis, particularly pertaining to disease resistance, has received limited attention. We exposed adult Bombus impatiens bumble bee workers to simulated, ecologically relevant heatwave or control thermal regimes and assessed longevity, immunity, and resistance to concurrent or future parasite infections. We demonstrate that survival and induced antibacterial immunity are reduced following heatwaves. Supporting that heatwave exposure compromised immunity, the cost of immune activation by a non-pathogenic elicitor was thermal regime dependent, with costs to long-term survival in control but not heatwave exposed bees. However, in the face of real infections, an inability to mount an optimal immune response will be detrimental, which was reflected by higher infections from trypanosome parasite exposure following the heatwave, relative to the control regime. These results demonstrate interactions between heatwave exposure and bumble bee performance, including immune and infection outcomes. Thus, the health of bumble bee pollinator populations may be affected through altered interactions with parasites and pathogens, in addition to other effects of extreme manifestations of climate change.See the uploaded readme file (README_Tobin_heatwave_data.txt).Funding provided by: National Institute of General Medical SciencesCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000057Award Number: R15 GM129681-01Funding provided by: U.S. Department of AgricultureCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000199Award Number: 2017-67013-2653