The impact of climate change on the energetics of primitively eusocial paper wasps

The ongoing climate change is suggested to have great impact on ecosystems and animal survival. Predicting how species respond to climate change is a foremost concern of global change scientists. Temperature is arguably the most important environmental variable driving the physiological rates of ectotherms. Ectothermic animals are considered particularly susceptible to environmental change because their body temperature and thus physiological performance vary acutely with environmental conditions. Paper wasps are heterothermic insects which are often in their lifecycle ectothermic (body temperature similar ambient), or only weakly endothermic (body temperature slightly elevated). The metabolism of ectothermic insects is temperature-dependent and warmer temperatures disproportionately affecting their energy balance. Thus metabolism is a crucial parameter for the survival in a changing environment. We will use the genus Polistes as a model organism for energetic investigations. The aim of this study is to investigate the vulnerability of paper wasps to climate change. Three Polistes species will be used in this study, originating from differing climate regions and/or habitats. We will investigate their metabolic response in dependence on temperature. Results will reveal whether species vary in their vulnerability and are differently threatened due to climate warming. The combination of environmental data, behavioural observations and metabolic data will be used to calculate the energetic demand for the colony during the breeding season and for the queens during overwintering in their hibernaculum. Environmental data of the habitats and microclimatic data at the nests will be measured throughout the breeding season. Temperature recordings are the basics for metabolic calculations. Behavioural observations will reveal the wasps daily activity patterns, which are necessary for calculations. The measured wasps CO2-production (metabolic data) in dependence on temperature will enable calculation of the energetic demand. Metabolism will be determined for resting, active and flying wasps and for the queens. The energy stores with which the queens enter dormancy must provide for basal metabolism throughout the winter period. Warmer winter temperature means higher costs for the basal metabolism and the question rises whether the energy stores will be sufficient at future climate conditions. For a reliable calculation of the wasps metabolism the microclimatic temperatures at the nest and in the habitat are the most relevant data. The energetic calculations will be performed with these data for actual and future predicted climate conditions. Future climate conditions will be taken according the predictions of the Intergovernmental Panel of Climate Change (IPCC), and for the local climate in Austria, the predictions of the Austrian Panel of Climate Change (APCC).

The ongoing climate change has great impact on ecosystems, animal distribution and survival. Predicting how species respond to climate change is a foremost concern of global change scientists. Temperature is arguably the most important environmental variable driving the physiological rates of ectotherms. Ectothermic animals are considered particularly susceptible to environmental change because their body temperature and thus physiological performance vary acutely with environmental conditions. Paper wasps of the genus Polistes have been chosen as model organisms for energetic investigations. These primitively eusocial insects, which live in small colonies with division of labour, are important predators of insect pests in agricultural ecosystems. Polistes wasps are often ectothermic in their life cycle (body temperature resembles ambient temperature) or only weakly endothermic (body temperature slightly elevated above ambient). The metabolism of ectothermic insects is temperature-dependent, warmer temperatures disproportionately affecting their energy balance. Thus metabolism is a crucial parameter for the survival in a changing environment. The aim of this study was to investigate the vulnerability of paper wasps from different climates to climate change. We compared two species (Polistes dominula, Polistes gallicus) from the Mediterranean climate in Italy with one species (Polistes dominula) from the temperate and one (Polistes biglumis) from the mountainous climate in Austria. The respiratory response (CO2 production) measured in dependence on temperature uncovered unknown evolutionary adaptations of metabolic processes to the different climate conditions in the wasps' habitats. In summer individuals, the montane species (P. biglumis), living in a colder environment, displayed a considerably lower metabolism than the lowland species (P. dominula and P. gallicus), which helps them to save energy in their harsh environment and short breeding season. In overwintering queens, by contrast, the Mediterranean species had a lower metabolism than the species from the cooler temperate climate. This adaptation helps them to save energy in their warmer overwintering environment. In a comprehensive approach the combination of metabolic results with environmental data and behavioural observations allowed calculation of the wasps' energetic demand during the breeding season, and of the queens during overwintering in their hibernaculum. These calculations were compared with the depletion of the queens' energy stores during winter, which provide for their basal metabolism. Results revealed that the species differ considerably in their metabolism and energetic demand, which makes them differently vulnerable to climate change. These findings are used for a model in progress to calculate the energetic demand for actual and future predicted climate scenarios, according to the predictions of the Intergovernmental Panel on Climate Change (IPCC), and for the local climate in Austria by the Austrian Panel of Climate Change (APCC). Results will reveal whether species vary in their vulnerability and are differently threatened due to climate warming in future.