Meeting Abstract

15.5  Tuesday, Jan. 4  Spiracle control by CO₂ in moth pupae – Is pH the hidden trigger? FöRSTER., T. D.*; HETZ, S. K.; Humboldt Universität Berlin, Germany; Humboldt Universität Berlin, Germany thomas.foerster@mso.umt.edu

When metabolic rate is low, many insects switch to a periodic breathing pattern known as discontinuous gas exchange cycles (DGC). A single DGC is subdivided into three phases – constricted, fluttering and open. The latter phase is controlled by carbon dioxide, although how this control is effected is largely unknown. One possibility is that changing levels of CO₂ in the hemolymph and tissues drive concurrent changes in pH, which itself affects behavior of the spiracles. To test this idea, we developed a compartmental model that captures the most important respiratory transport and storage processes of CO₂. A key component was the assumed simple on-off type control of the spiracle aperture by hemolymph pH. For physiologically reasonable parameters, the model showed oscillations in gas exchange remarkably similar to a DGC pattern without fluttering phase. If metabolic rate or spiracle conductance had been varied, bifurcation analysis of the model revealed a qualitative change to continuously open spiracles that matches earlier experimental observations (Bradley, 2008, in Adv. Exp. Med. Biol., 618, 211-220; Hetz, 2007, Comp. Biochem. Physiol. A, 148(4), 743-754). The model indicates that DGC might be a purely passive pattern resulting from the discrete control of the spiracle aperture and the slow dehydration of CO₂. Given these, a relatively simple pH trigger could be sufficient to generate the cyclic gas exchange pattern known as DGC.