Aestivation in the Indian apple snail Pila—I. Adaptation in natural and experimental conditions

Abstract

1. 1. The Indian apple snail Pila aestivates winter and summer for a total period of about 6 months a year when the ponds and fields dry up and the temperature exceeds the vital limits of the active snail. 2. 2. The animals are active in water between 25°C and 35°C but are not able to tolerate 20°C and 40°C, the usual extreme winter and summer temperatures. Burrowing into the mud in winter and summer is an adaptation to these climatic changes. 3. 3. An animal out of water aestivates after a period of activity. The duration of activity depends upon the relative humidity of the environment. 4. 4. The onset and cessation of aestivation at any temperature within the favourable range depend soley on the availability of water. 5. 5. The presence of a moderately thick shell ( 1 1 2 mm ) with a tight-fitting operculum minimizes water loss. 6. 6. In the aestivating condition, humidity affects neither the survival nor loss of weight of the animals. 7. 7. When an animal is forced to aestivate with a portion of the shell or operculum removed so as to expose the soft parts, the animal loses water and does not survive more than 10 days. At death the water content is between 55 and 60 per cent of the total soft body weight. 8. 8. The shell is resistant to the passage of water and electrolytes. Water only at the opercular region, where the junction with the shell is sealed with mucus, initiates the return to an active state.