Evolution of the Mechanisms Underlying Insect Respiratory Gas Exchange
Abstract Many factors influence gas exchange patterns in insects and are generally treated in isolation from one another. Here, we provide a review of the current state of knowledge on the physics of gas exchange, insect respiratory chemoreceptors, the diversity and the methods typically used in the characterisation of respiratory pattern types, briefly covering some of the new tools and techniques that are being incorporated into this field. We then discuss the functional significance of insect gas exchange pattern variation, and possible evolutionary explanations of discontinuous gas exchange as a derived control mechanism for effecting physiological change in the context of (a) adaptive hypotheses, (b) non-adaptive hypotheses and (c) mathematical modelling of gas exchange. The lack of consensus in the literature for all proposed adaptive or mechanistic hypotheses suggests that multiple factors influence which gas exchange pattern is displayed by any particular insect during a given experiment. Thus, while the primary function of a breathing pattern is to meet an animal's gas exchange requirements, it is an interacting hierarchy of constraints that most likely determines how this demand may be met. We conclude the review with a brief discussion of future directions for the field.