These results illustrate that the degree to which acoustic signals are altered by Ta varies with individual species. And so began the analysis of temperature and acoustic insects.
Temperature is a physical variable that affects all aspects of animal life. Animals are able to function because the various chemical reactions necessary for life are able to proceed at sufficient rates to maintain life processes. However, the rates of these chemical reactions are also temperature dependent. The ability of insects to produce acoustic signals is dependent on chemical reactions occurring at a specific rate, so that the mechanisms producing and receiving sound function properly. Therefore, temperature will affect acoustic insects at a subcellular level, but these effects will influence the abilities of populations to communicate effectively.
The rate of chemical reactions varies with temperature in a predictable fashion. The Q10 effect describes how reaction rates vary over a 10°C temperature change. The relationship is described by equation 7.3:
where kj and k2 are the rates of chemical reactions at temperatures T\ and T2 and should be about two in the normal temperature range of animal activity (Withers, 1992). This relationship between temperature and chemical reaction rates means that insect communication systems will be altered by changes in temperature. Acoustic insects must be able to deal with changes in temperature if they are going to communicate over a range of Ta. If a species cannot adjust to changes in Ta, there will be only a small range over which they can communicate and this will limit the usefulness of sound as a reproductive signal.
Acoustic insects have two potential strategies with respect to changes in ra. They can allow their body temperature (Th) to fluctuate with the environment to be a thermoconformer (historically a poikilotherm or cold-blooded animal) or they can regulate Th independent of ra and be a thermoregulator. Thermoconformers must be able to adjust receiver preferences as ra alters the call structure through the Q10 effect in order to maintain a response to the altered signal. Thermoregulators can avoid any temperature effects on call structure or receiver preferences since these can maintain Th in a narrow range so that there will be minimal variation in call parameters as ra changes. The implementation of specific thermoregulatory strategies by particular groups of acoustic insects will be influenced by physical factors.
Animals exchange heat with the environment based on the physical mechanisms of heat transfer. The small body size and high surface-to-volume ratio of most insect species means that they will exchange heat with the environment quickly. This fact will have significant influence on the thermoregulatory strategy employed by the insects. Small insects (e.g. planthoppers) will have difficulty in maintaining a thermal gradient from ra. In effect the physics of heat transfer will cause these animals to be thermoconformers and the receivers must be able to compensate for the changes in the acoustic signals which will result with changes in Th as a result of changes in ra. Larger insects (e.g. cicadas) will be able to maintain a thermal gradient from ra and can avoid temperature effects on call structure since they can regulate their Th (e.g. Villet et al., 2003).
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