Temperature insensitive O2 in blood of the tree frogChiromantis petersi

Abstract

Respiratory gas exchange and blood respiratory properties have been studied in the East-African tree frogChiromantis petersi. This frog is unusually xerophilous, occupies dry habitats and prefers body temperatures near 40°C and direct solar exposure. Total O2 uptake was low at 81 μl O2·g−1·h−1±19.0 (SD) at 25°C increasing to 253.5 μl O2·g−1·h−1±94.8 (SD) at 40°C giving aQ 10 value of 2.1. Skin O2 uptake at 25°C was 38.5% of total. The gas exchange ratio was 0.71 for whole body gas exchange, 0.61 for the lungs and 1.02 for the skin at 25°C.

Blood O2 affinity was low with aP 50 of 47.5 mmHg at 25°C and pH 7.65. Then H-value at 25°C increased from 2.7 aroundP 50 to 5.0 at O2 saturations exceeding 70–80%. Surprisingly, blood O2 affinity was nearly insensitive to temperature expressed by a ΔH value of ±1.0 kcal·mole between 25 and 40°C.

The adaptive significance of the low O2 affinity, the increase ofn H with O2 saturation and the temperature insensitive O2-Hb binding is discussed in relation to the high and fluctuating body temperatures ofChiromantis