PhDThis work is concerned with processes of thermal acclimation in the freshwater pulmonate, Lymnaea stagnalis. Three physiological functions
were studied: heart rate, rate of oxygen consumption and assimilation
efficiency, Seasonal changes in rate-temperature curves of the first two
processes were investigated and compared with alterations induced by exposure
to constant temperatures in the laboratory. Simple comparisons were made
to determine whether season affected assimilation efficiency. The aims
of the investigation were to show whether the measured physiological functions
exhibited acclimatory responses to determine the precise nature and interrelationship
of any such adaptations, and to suggest possible mechanisms
responsible for the changes.
It was found that changes in the heart rate-temperature relation
were induced both by season and by laboratory acclimation. Results of the
seasonal study showed apparent capacity adaptations, so that winter animals
had a higher heart rate than summer animals at temperatures between 15 and
25 degrees C, and also resistance adaptations, which gave summer animals increased
resistance to heat and winter animals greater tolerance of cold.
Laboratory acclimation induced resistance adaptations at both temperature
extremes but capacity adaptation was absent. Observed bimodality in heart
rate-temperature curves of both studies indicated that control of heart
rate is complex. These results are discussed further with reference to
changes in physiological mechanisms.
Seasonal changes occurred in the size-rate regression for oxygen
consumption and in the general shape of the rate temporature curves.
There was evidence for a 'reverse acclimation' in response to seasonal
changes in temperature. These seasonal responses were not produced,
however, by exposure to constant temperature in the laboratory. It is
proposed that the observed changes resulted essentially from reproductive
activity and seasonal changes in dietary conditions. Hormonal influences
are thought to be most important in mediating these changes. No significant differences were found in the assimilation
efficiencies of winter and summer snails. Results of this and other
studies suggest that the assimilation function does not show acclimatory
changes in response to either temperature or season.
The results are discussed in relation to the known biology of
Lymnaea stagnalis and with reference to fundamental temperature acclimation