Water balance in the semiaquatic beetle, Peltodytes muticus

Abstract

1. 1. The rates for water uptake and loss for Peltodytes muticus in both an aquatic and a terrestrial environment were monitored by tracing tritium labelled water. 2. 2. Uptake rate of water for animals in an aquatic environment was 0.28 to 0.35 mg/hr and beetles turned over 9–11% body water/hr. Rate constants for water loss were proportional to the water activity and temperature of the external aquatic media. Water loss rates in a terrestrial environment over a range of 0.0–0.95 a v were independent of ambient water vapor activity. 3. 3. At comparable conditions, rate constants for water loss were the same for both aquatic and terrestrial conditions. 4. 4. Critical lower water limits were as low as 11% of equilibrium body water content and the beetles were able to sorb water actively from unsaturated ambient air.