Fisiologiese aspekte van anhidrobiese by die varswaterslak Bulinus [Bulinus] tropicus [Krauss]

Abstract

Certain physiological aspects of Bulinus (Bulinus) tropicus (Krauss), a member of the freshwater pulmonates, in a waterless environment have been studied. To escape severe drought in their natural habitat, these snails remain in a state of dormancy until the return of the rains. In the laboratory B. tropicus was removed from the water and kept at 15°c. Experiments concerning the physiological adaptations of these snails to a waterless environment were carried out at 96%, 92% , 85%, 74% and 57% relative humidity. The weight loss of snails were measured up to 60 days without water. During the first twenty days a rapid weight loss was observed which declined steadily from twenty to sixty days. At the high relative humidities the survival rate was higher. At 57% relative humidity all snails were dead after 30 days out of water. The blood osmotic pressure increased with time at both 96% and 85% relative humidity, though not at the same rate. The sodium and potassium concentrations of the tissues also increased after the snails had been removed from water, though at a far lesser rate than the blood osmotic pressure. The rate of oxygen consumption of snails removed from water have also been studied and it was concluded that to successfully maintain itself in a waterless environment, the rate of oxygen consumption of B. tropicus should drop to more or less 35% of the value for normal snails. The water loss which these snails experience in a waterless environment is not entirely due to the water loss through the mouth aperture of the shell. The shell is itself also permeable to water to a lesser extent.