Why do models of insect respiratory patterns fail?

Abstract

Insects exchange respiratory gases using an astonishing diversity of patterns. Of these, discontinuous gas exchange cycles (DGCs) have received the most study, but there are many other patterns exhibited intraspecifically and interspecifically. Moreover, some individual insects transition between patterns based on poorly understood combinations of internal and external factors. Why have biologists failed, so far, to develop a framework capable of explaining this diversity? Here, we propose two answers. The first is that the framework will have to be simultaneously general and highly detailed. It should describe, in a universal way, the physical and chemical processes that any insect uses to exchange gases through the respiratory system (i.e. tracheal tubes and spiracles) while simultaneously containing enough morphological, physiological and neural detail that it captures the specifics of patterns exhibited by any species or individual. The second difficulty is that the framework will have to provide ultimate, evolutionary explanations for why patterns vary within and among insects as well as proximate physiological explanations for how different parts of the respiratory system are modified to produce that diversity. Although biologists have made significant progress on all of these problems individually, there has been little integration among approaches. We propose that renewed efforts be undertaken to integrate across levels and approaches with the goal of developing a new class of general, flexible models capable of explaining a greater fraction of the observed diversity of respiratory patterns.

Oxygen limitation is not the cause of death during lethal heat exposure in an insect

“…While indeed there was a strong relationship between ambient pO 2 and haemolymph pO 2 for 30 min prior to death, haemolymph pO 2 remained stable through this period, as well as for the subsequent 30 min. This is likely owing to a range of plastic compensatory mechanisms operating over a large thermal range, most likely owing to highly effective convection-based gas exchange in the tracheal system [6].…”

“…Oxygen limitation is proposed as a major mechanistic determinant of animal thermal tolerance and, hence, vulnerability to climate change. However, the applicability of the broader theory of oxygen-and capacity-limited thermal tolerance (OCLTT, sensu Pörtner [1]) to the highly diverse and functionally important Insecta is particularly controversial [2][3][4][5], mainly since they possess highly efficient respiratory systems, can readily transition between diffusive-or convectiondominated gas exchange [6] and can show pronounced metabolic responses to their environmental conditions (e.g. when maintaining flight [7]).…”

Respiratory gas levels interact to control ventilatory motor patterns in isolated locust ganglia

“…Modulation of ventilatory motor patterns is well exemplified in insect discontinuous gas exchange (DGE). This well-studied insect gas exchange pattern is exhibited during periods of quiescence or at low metabolic rates (reviewed in Chown, 2011;Chown et al, 2006;Contreras and Bradley, 2009;Lighton, 1996;Matthews, 2018;Terblanche and Woods, 2018). It comprises three phases, defined by the spiracle state as reflected by CO 2 emission rate: closed, flutter and open.…”

Water Costs of Gas Exchange by a Speckled Cockroach and a Darkling Beetle

“…CGE and cyclic are the ancestral patterns, as all spiracles do not seal completely or simultaneously during gas exchange. In CGE, the spiracles remain open and the gas exchange is regular, often to support maximum gas exchange in active species [8][9][10]. Cyclic gas exchange consists of alternating burst and interburst phases that produce periodic gas exchange, but the spiracles never close completely and simultaneously [11].…”