Meeting Abstract

P2.107  Jan. 5  Respiratory responses of the Giant hissing cockroach, Gromphadorhina portentosa to hypobaric hypoxia JOOS, Barbara*; LIGHTON, John RB; THOMBRE, Rhadha M; Sable Systems International Inc; Sable Systems International Inc; Sable Systems International Inc joos@sablesys.com

Insects use a diffusion-based tracheal system as the primary gas exchange organ and, in most cases, do not have respiratory pigments. This direct delivery system has some functional advantages at small body sizes but it is thought that there are practical limits to the body sizes that can be maintained with a purely-diffusion based respiratory system. It has been proposed that the insect gigantism seen in the Paleozoic was possible only because of elevated atmospheric oxygen levels (Graham et al. 1995 and others). If the structure of the insect respiratory system does limit oxygen delivery, hypoxic conditions (.e.g. at altitude) should represent a greater challenge for larger insects. We have developed a new technique for measuring flow-through carbon dioxide emission and total body water loss under hypobaric conditions in the Hissing Cockroach, Gromphadorhina portentosa. Adult G. portentosa may be as large as 9g and have body lengths of 40-55 mm. G. portentosa , like all roaches is hemimetabolous and comparisons between adults and the earlier instars can be used to separate body size effects from other those of evolutionary history. Initial results show that G. portentosa are surprisingly insensitive to hypobaric conditions and that extended exposures to 5 psi (35kPa) total pressure, equivalent to an altitude of >7700m, does not affect adult survivorship. Neither carbon dioxide emission nor water loss rate in adult G. portentosa was significantly affected by decreasing atmospheric pressure over the range from 52 to 86 kPa. Lowered oxygen partial pressures apparently do not constitute a barrier to effective gas exchange by diffusion at least in adult. G. portentosa.