Hold your breath beetle-Mites!

Abstract

Respiratory gas exchange in insects occurs via a branching tracheal system. The entrances to the air-filled tracheae are the spiracles, which are gate-like structures in the exoskeleton. The open or closed state of spiracles defines the three possible gas exchange patterns of insects. In resting insects, spiracles may open and close over time in a repeatable fashion that results in a discontinuous gas exchange (DGE) pattern characterized by periods of zero organism-to-environment gas exchange. Several adaptive hypotheses have been proposed to explain why insects engage in DGE, but none have attracted overwhelming support. We provide support for a previously untested hypothesis that posits that DGE minimizes the risk of infestation of the tracheal system by mites and other agents. Here, we analyze the respiratory patterns of 15 species of ground beetle (Carabidae), of which more than 40% of individuals harbored external mites. Compared with mite-free individuals, infested one's engaged significantly more often in DGE. Mite-free individuals predominantly employed a cyclic or continuous gas exchange pattern, which did not include complete spiracle closure. Complete spiracle closure may prevent parasites from invading, clogging, or transferring pathogens to the tracheal system or from foraging on tissue not protected by thick chitinous layers.

A "clean" alien species? Parasites of the invasive ladybird Harmonia axyridis (Coleoptera: Coccinellidae)

“…Phoresy is a specifi c nonparasitic relationship, wherein the mites (Acarina) use different taxonomic groups of animals only for transport (Gwiazdowicz, 2000). Nonetheless, phoresy is a strong stressor for the host insect (Gudowska et al, 2015). Moreover, mites could be vectors of a wide range of bacterial, fungal and protozoan pathogens or viruses (Poinar & Poinar, 1998).…”

Mass scaling of metabolic rates in carabid beetles (Carabidae) – the importance of phylogeny, regression models and gas exchange patterns

“…Of the day and night measurements of each individual beetle, only the one (day or night) with the lower MR was selected for further analysis. Three different gas exchange patterns -DGE, cyclic and continuouswere determined based on the VĊ O2 , as defined by Marais et al (2005) and Chown (2011) with modifications by Gudowska et al (2016Gudowska et al ( , 2017. First, the gas exchange patterns were classified as continuous when half or more of the records were above the average value, and second, periodic patterns (DGE or cyclic) were recognized as regular peaks and troughs in gas exchange and when less than 30% of the data was above the average.…”

“…For example, during a resting and postabsorptive state, some insects employ the discontinuous (DGE), cyclic or continuous gas exchange modes (Marais et al, 2005). In some species of mite-free beetles, ants and grasshoppers, DGE is associated with lower MRs (Gibbs and Johnson, 2004;Gudowska et al, 2016;Huang et al, 2015), whereas in cockroaches and caterpillars, no significant differences in the rate of CO 2 release (VĊ O2 ) have been reported (Groenewald et al, 2013;Williams et al, 2010). Interestingly, engagement in a given gas exchange pattern can depend on biotic and abiotic environmental factors (reviewed in Chown et al, 2006;Contreras et al, 2014;White et al, 2007a).…”

“…Interestingly, engagement in a given gas exchange pattern can depend on biotic and abiotic environmental factors (reviewed in Chown et al, 2006;Contreras et al, 2014;White et al, 2007a). For example, DGE has been hypothesized to be a response to habitat aridity (Buck, 1953;Huang et al, 2015;Lighton, 1996;Sláma et al, 2007;Terblanche et al, 2008a), a hypoxic and/or hypercapnic environment (Lighton, 1998;Lighton and Berrigan, 1995) and parasite infestation (Gudowska et al, 2016;Miller, 1974).…”

The closed spiracle phase of discontinuous gas exchange predicts diving duration in the grasshopper, Paracinema tricolor

“…There is a well-established suite of factors determining insect respiratory patterns: (1) primarily maintaining oxygen supply, then (2) pH regulation (and CO 2 excretion), and, finally, (3) water saving and/or minimising oxidative damage (Groenewald et al, 2014). It is reasonable that spiracle closure during DGE for water saving could also restrict unwanted foreign bodies from entering the tracheal system, as recently demonstrated in carabid beetles (Gudowska et al, 2015). An alternative novel hypothesis that we propose here is that spiracle closure may provide an advantage by restricting respiratory water loss, but at the same time by keeping water from entering the tracheal system during immersion.…”