Energetics and thermal tolerance of paper wasp brood

Climate change is expected to produce shifts in species distribution as well as behavioural, life- history, and physiological adjustments to find suitable conditions or to cope with the altered environment. Temperature is arguably the most important environmental parameter for the survival of ectothermic insects. How they respond to temperature change will determine their persistence in variable environments. Metabolic rate is a key component of insects energy budgets and is a crucial parameter for their survival. Paper wasps are primitively eusocial insects, which are heterothermic in principle, but they are often in their lifecycle ectothermic. This means their body temperature often resembles ambient temperature. They are a model organism for behavioural studies and they are well appropriate for ecophysiological investigations on physiological adjustments to microclimate conditions in their habitat and the impact of climate change on survival. The aim of the study is to explore the vulnerability of paper wasp brood (larvae and pupae) from different climates to global warming. We will investigate the adjustments of thermal tolerance traits and energetic demand to differing environments. Results will reveal the threaten due to global warming for these insects and the varying degrees of success to respond to temperature increase. The study will be conducted with species from the Mediterranean climate (Polistes dominula, Polistes gallicus), the central European temperate area (P. dominula) and an alpine species (P. biglumis). The respiratory metabolism (CO2 production) of larvae and pupae will be measured. The upper and lower thermal limits of survival will be determined by thermolimit respirometry, a method which determines the end of respiration. The response to heat and cold stress will be quantified by measuring the upregulation of a heat shock protein (hsp70). These are special proteins which protect the tissues from damage. Body temperature and microclimate measurements at the nests will enable an assessment of the temperature stress of the colonies at current and future climate conditions. The investigation of thermal traits in relation to microclimate conditions will enable predictions on the impact of climate change on these insects. Together with the findings of our last project on thermal and metabolic traits of adult paper wasps, they could be established as model organisms in energetic research in primitively eusocial insects. The study will be conducted by the working team ecophysiology (H. Kovac, A. Stabenteiner) at the Institute of Biology at the University of Graz in Austria, and the investigations on heat shock proteins will be conducted by Jesper Givskov Sørensen from the Department of Bioscience of the Aarhus University in Denmark.

Temperature is an important parameter that determines the physiological processes of animals. How flexibly organisms can respond to temperature changes has a major impact on their survival in an environment altered by climate change. We chose the widely distributed paper wasps for our investigations. The aim of this studies was to investigate the adaptation of the brood (larvae and pupae) of different paper wasp species to their respective microclimates and to assess the effect of climate change. We investigated how they are adapted to their different habitats in terms of their metabolism and thermal resilience. By calculating the energy requirements for an entire season, we were able to show how severely the different species are threatened by a rise in temperature. The studies were conducted with species from the Mediterranean climate (Polistes dominula, Polistes gallicus), the temperate climate of Central Europe (Polistes dominula), and an alpine species (Polistes biglumis). Metabolism was determined by measuring carbon dioxide production. The upper thermal lethal limit was determined respiratorily (cessation of respiration) and the molecular response to heat stress was investigated by determining heat shock proteins. The microclimate at the nests was measured in order to calculate the energy costs of the colonies under current and future climatic conditions. Metabolism was measured across the entire temperature range (5-45 C) to which the wasps are exposed to during a season (May-September). Surprisingly, the three species had very similar metabolic rates in both larvae and pupae. CO production was lowest at cool temperatures and then increased exponentially as the temperature rose. Larvae and pupae had very similar metabolic rates, which was also surprising, as in other insects the larvae usually have a higher metabolism. The critical thermal maxima (lethal limit) were very similar for all species, ranging between 47.6 and 48.8C. An experimental heat stress of 45C caused increased production of heat shock proteins, which are designed to repair potential damage. However, the different species reacted differently to the heat stress. Calculations of the energy requirements of larvae and pupae using metabolic and microclimate data showed that native wasps from temperate climates and Mediterranean wasps have approximately the same energy requirements during a season, whereas the alpine species has significantly lower requirements. We suspect that this is an adaptation to the less favorable weather conditions, which limit their ability to forage. This shows that the animals have adapted optimally to the microclimatic conditions by developing an energy-saving lifestyle. Calculations based on higher temperatures under future climate scenarios showed that the energy requirements of the wasps generally increase, with the alpine species showing the strongest increase. This species is therefore most threatened by climate change.