Long-term and acute effects of temperature and oxygen on metabolism, food intake, growth and heat tolerance in a freshwater gastropod

Abstract

Temperature affects the physiology and life-history of ectothermic animals, often increasing metabolic rate and decreasing body size. Oxygen limitation has been put forward as a mechanism to explain thermal responses of body size and the ability to survive stress. However the time-scales involved in growth performance and heat tolerance differ radically. In order to increase our understanding of oxygen and temperature effects on body size and heat tolerance and the time scale involved, we reared Lymnaea stagnalis under six combinations of temperature and oxygen tension from hatching up to an age of 300 days and recorded shell length during this whole period. At the end of this period, we determined scope for growth by measuring food intake rate, assimilation efficiency, respiration rate and ammonium excretion rate at two different temperatures. We also measured the snails' ability to survive heat stress (CTmax), both at normoxia and hypoxia. We found that scope for growth and long term growth performance were much more affected by interactions of chronic oxygen and temperature conditions during rearing than by acute conditions during testing. Furthermore, our study shows that individual variation in growth performance can be traced back to individual differences in rates of food and oxygen consumption. Developmental acclimation also gave rise to differences in CTmax, but these were relatively small and were only expressed when CTmax was tested under hypoxia. The large effects of rearing oxygen conditions on growth and other physiological rates compared to modest effects of test oxygen conditions on CTmax suggest that small effects of hypoxia on the short term (e.g. heat tolerance) may nevertheless have large repercussions on the long term (e.g. growth and reproduction), even in a pulmonate snail that can compensate for hypoxia to some extent by aerial respiration.

Sublethal heat reduces overall reproductive investment and male allocation in a simultaneously hermaphroditic snail species

“…We did not find an effect of heat on growth in our experimental design. However, it is likely that, if we had kept the snails under heat treatment for a longer period, we would have detected such a difference (e.g., Leicht et al 2013; Hoefnagel and Verberk 2017; Salo et al 2019). The trend that the snails at 28 °C show might be seen as a confirmation for this previously reported response, and is not surprising given their increased metabolic rate due to the temperature increase.…”

A thermal stressor, propranolol and long-term memory formation in freshly collected Lymnaea

“…We have not attempted to acclimatize Lymnaea in the laboratory to higher temperatures close to their thermal tolerance upper limit of 30°C (Vaughn, 1953;Salo et al, 2019) and then determine whether the HS has the same effect on LTM formation. Rearing temperature was shown by Hoefnagel and Verberk (2017) not to alter the upper limit of heat tolerance in Lymnaea, and the authors concluded that long-term acclimation had limited capacity to improve heat tolerance. In the freshly collected snails used here, however, although they may experience temperatures greater than 25°C for hours during daytime in summer, that experience does not prevent heat from acting as a stressor.…”

Laboratory-Based Comparison for the Effects of Environmental Stressors Supports Field Evidence for the Relative Importance of Pollution on Life History and Behavior of the Pond Snail, Lymnaea stagnalis

“…At present, we cannot determine the reason that L. stagnalis failed to exhibit avoidance behavior in response to the high temperature exposure, however, there are several possible explanations for this. First, the high temperature stressor may not have been recognized as a threat since L. stagnalis has a large range for thermotolerance . Second, the temperature above the water line may not have differed markedly compared to the temperature in the beaker due to the heat of the water bath.…”

“…First, the high temperature stressor may not have been recognized as a threat since L. stagnalis has a large range for thermotolerance. 51 Second, the temperature above the water line may not have differed markedly compared to the temperature in the beaker due to the heat of the water bath. Third, increased temperature may have reduced the crawl out behavior if there was a perceived desiccation risk associated with warmer conditions.…”