Meeting Abstract

P3.121  Jan. 6  Effect of CO₂ and development on the acid-base status of a cave dwelling beetle pupa KAISER, A.; Midwestern University, Glendale, AZ akaise@midwestern.edu

Zophobas rugipes lives in caves under a layer of bat guano, where hypercapnic and hypoxic conditions can occur. The pupae of Zophobas display elevated metabolic rates at the beginning and at the end of the pupal stage. CO₂ is released cyclically in short open phases. Between open phases CO₂ release is reduced by spiracular closure. These characteristics lead to an increased amount of stored CO₂ within the organism, resulting in hemolymph and tissue acidosis. To characterize the respiratory and metabolic compensation for long-term acidosis, I analyzed acid-base parameters in vitro. To determine the effects of CO₂ retention during spiracular closure, I synchronously measured CO₂ release and pH in vivo. The chemical solubility of CO₂ in tissue and hemolymph were the highest ever detected in insects. CO₂ solubility remained unchanged during the entire pupal stage, which suggests that there was no metabolic regulation of acid-base parameters. Increased CO₂ production was compensated for by increased cycle frequency. The respiratory cycles had little effect on acid base status. A typical accumulation of 100 nmol CO₂ g^-1 increased the internal Pco₂ by 0.2 kPa. The correlated decrease in pH and [HCO₃^–] were 0.01 units and 0.1 mmol l^-1 in hemolymph, and 0.003 units and 0.2 mmol l^-1 in tissue, respectively. Respiratory control of CO₂ release is the major mechanism used by Zophobas pupae to control acid-base balance over a wide range of metabolic levels. High buffering capabilities of the tissue and hemolymph maintain stable acid-base status during cyclic respiration and throughout the pupal stage. This may be a preadaptation to their cryptic life in caves, where hypercapnic and hypoxic conditions can occur.