Temperature Effects on Haemolymph Acid-Base Status in vivo and in vitro in the Two-Striped Grasshopper Melanoplus Bivittatus

Abstract

ABSTRACT In this study, I examine the effect of temperature on haemolymph acid-base status in vivo and in vitro in the two-striped grasshopper Melanoplus bivittatus. Melanoplus bivittatus experience wide (up to 40 °C) diurnal body temperature fluctuations in the field, but maintain body temperature relatively constant during sunny days by behavioural thermoregulation. Haemolymph pH was statistically constant (7·12) between 10 and 25°C, but decreased by –0·017 units °C− 1 from 25 to 40 °C. Relative alkalinity and fractional protein dissociation were conserved only at body temperatures at which feeding and locomotory activity occur, above 20°C. Haemolymph total CO2 (Ctot) increased from 10 to 20°C and decreased from 20 to 40°C. Haemolymph increased from 10 to 20°C and was statistically constant between 20 and 40°C. Carbonic acid pKapp in haemolymph was 6·122 at 35 °C, and decreased with temperature by –0·0081 units °C− 1. Haemolymph buffer value averaged – 35mequivl− 1pHunit− 1. Haemolymph pH changes with temperature were small (less than –0·004 units °C− 1) in vitro at constant . Therefore, passive physicochemical effects cannot account for the pattern of acid-base regulation in vivo. The temperature shift from 10 to 20°C was accompanied by a net addition of 4·2–0·2 mmol I− 1 of bicarbonate equivalents to the haemolymph. The temperature shift from 20 to 40°C was accompanied by a net removal of 10–14 mmol I− 1 of bicarbonate equivalents from the haemolymph. Haemolymph acid-base regulation in vivo during temperature changes is dominated by active variation of bicarbonate equivalents rather than by changes in as observed for most other air-breathers.