The critical thermal tolerance traits of respiration and the energy metabolism of insects

Temperature, meant as average temperature throughout the year as well as the immediate local microclimate condition (minimum and maximum temperature), is a crucial abiotic environmental factor, directly affecting an individual`s biochemical and physiological processes. The individual`s thermal tolerance range is therefore of great importance for the fitness and survival of a species. Knowledge of the thermal tolerance is crucial to our understanding of ecology, evolution, and physiology because these traits play an important role in determining the species range distributions. In this project I will investigate the thermal tolerance traits in insects` respiration and the dependence of energy turnover on ambient temperature. Respiration is one of the fundamental physiological processes, directly involved in metabolism and energy supply. Investigations on respiration are therefore an appropriate tool to assess the individuals` thermal tolerances. To understand the response of organisms to a changing environment due to global warming, which directly affects the temperate climate of Central Europe, the knowledge of the fundamental connections between temperature and respiration are absolutely indispensable. In this context the thermal ranges of native and (related) invasive animals are of special interest. Thermal tolerance traits include the upper and lower lethal temperatures and a range of non-lethal measurements including the high and low `critical thermal,` `knockdown` or `chill coma` temperatures. These traits will be determined with "thermolimit respirometry," a method of temperature-dependent respiration measurement and the accompanying activity monitoring. However, survival in a changing environment is not only determined by thermal limits. A higher metabolism caused by increased temperatures may be fatal if the energy supply is a limiting factor. Therefore, the temperature dependence of the animals` resting metabolism (also called "standard metabolic rate") will be determined in their entire natural thermal range. It is the baseline of the active metabolic power output, and as a typical energetic trait it enables the comparison of different species concerning their energetic performance. The sum of these evaluated thermal traits should enable an assessment of the thermal tolerance and a comparison of different species concerning their fitness and survival in a changing environment. The study aims to give an overview of the thermal traits of some native insects with ecological or economic relevance in the temperate climate region of Central Europe (Styria, Austria). For comparison, some invasive insect species will be included in the program. The taxa to be investigated will be ants, wasps, beetles and bugs. The results will deliver knowledge of global importance, because the study, for the first time, compares respiratory traits, metabolism and the ability to be active of local and related invasive insects in their whole viable temperature ranges.

The geographical distribution range, abundance, growth rate, survival and mortality of insects are strongly influenced by abiotic environmental factors like temperature. The temperature, in its significance as an annual mean temperature as well as in its microclimatic manifestation, directly influences the biochemical and physiological processes of the individuals. Respiration is one of the basic physiological processes directly involved in metabolism and energy supply. Studies on respiration are therefore a well-suited means to assess individual thermal tolerance and fitness. The knowledge about the thermal tolerance range is decisive for our understanding of ecology, evolution and physiology of insects. We investigated the thermal tolerance range of respiration and its general dependence on temperature of bees, wasps and other insects. It was shown in two European honeybee races that they have well adapted to local climatic conditions in the course of evolutionary process. The Italian Ligustica bee, where we evaluated a higher lethal temperature than in the native Carnica bee, is better adapted to the high temperatures of the Mediterranean climate. Due to this benefit it may have advantages under future climatic conditions with an increased number of heat waves. Investigations of the respiration of native paper wasps revealed their adaptations to the special microclimatic conditions at the nest. The measurement of the basal metabolism by means of the carbon dioxide release revealed an exponential increase in carbon dioxide emission with ambient temperature. Microclimatic temperature measurements at the nest showed that the insects are mostly in the lower temperature range of the determined basal metabolism curve. An increase in the average temperature would result in an exponential increase of the energy requirement, which can have severe consequences for the survival of the wasps. Comparative investigations of the thermal limits and nesting habits of the native paper wasp with a related, southern neighbouring species in Italy in the Mediterranean climatic area, revealed adaptations in the behaviour and physiology of the animals to the local climatic conditions. Such investigations have also been carried out on native and invasive bugs in Austria. Their ecophysiological adaptations of thermal tolerance and metabolism to the climatic conditions have been described and reasons for the range distribution success could be found. This knowledge of the fundamental relationships between environmental factors and physiological responses is indispensable to understand the reactions of organisms to climate warming and predictions concerning their future survival and distribution.