Meeting Abstract

65.5  Jan. 7  Discontinuous respiration as a response to oxidative damage: Tale of a sedentary insect CONTRERAS, H.L.*; BRADLEY, T.J.; Univ. of California, Irvine hcontrer@uci.edu

Insects have a relatively high mass-specific metabolic rate due their small size. It is surprising, therefore, that numerous taxa exhibit the discontinuous gas exchange cycle (DGC), a respiratory pattern in which the spiracles undergo a distinct closed phase. Recently it has been suggested that the DGC evolved to reduce O2 concentrations in the body, since oxygen (even at low levels) causes oxidative damage to tissues. Hetz and Bradley (2005) proposed that the efficient respiratory system of insects may have evolved to sustain large energy requirements needed for periods of high metabolic demand (e.g. during flight). DGC would be expected, therefore only during periods of low metabolic demand. We investigated the respiratory pattern of the Madagascar Hissing Cockroach (Gromphadorhina portentosa), a sedentary, non-flying insect. To examine the effects of changing metabolic rate, we subjected ten roaches to varying temperatures (10, 20, 30C) and recorded their respiratory pattern. Since G. portentosa, is relatively inactive, we expected to obtain maximal metabolic rates and a continuous respiratory pattern at higher temperatures. As temperatures decreased, the incidence of the DGC was expected to increase with decreases in metabolic rate. We found that closed phases became very rare at 30C. At lower temperatures the proportion closed phases increased. We conclude that metabolic rate dictates the insect�s respiratory pattern (where an increase in demand induces continuous respiration and a decrease elicits DGC) and the length of respiratory cycle (as temperature decreases the time spent in each bout increases).