Balancing the demands of physiological systems: digestion in crustaceans during environemental change

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The general effects of feeding on metabolism are well known (specific dynamic action, SDA), which is why they are usually controlled for in physiological experiments. However, if the energetic costs of digestion and assimilation are large they may impact other physiological systems. Because animals do not always stop feeding prior to experiencing an environmental perturbation, previous articles that do not consider digestive processes may not show the whole picture and may even be erroneous. My preliminary work has shown that the nutritional status an organism will affect other physiological processes. With this in mind this project will investigate physiological responses and digestive processes in three species of decapod crustacean of differing osmoregulatory ability when feeding and digest in different temperatures/low salinity regimes. We aim to 1) Determine how animals use cardiovascular (heart rate and regional blood flow) and respiratory mechanisms (oxygen uptake, blood-gas transport and acid-base) to balance the demands of competing physiological processes, and 2) Determine how the components of the specific dynamic action (mechanical digestion, enzyme activity, protein synthesis) contribute to the total SDA and to what degree they are modulated during temperature acclimation and low salinity exposure. These findings will help in understanding the partitioning and control of the phases of digestion that comprise SDA as well as how organisms balance the demands of competing physiological systems. The completion of the projects outlined in this grant will increase our understanding of digestive processes in crustaceans and should be of relevance for determining optimal culture conditions for aquaculture. There has been a renewed interest in recent years in studying the responses of organisms in a more natural setting or even in the field and these findings will extend this growing area of whole organism physiology and provide a framework for future studies. The completion of the projects outlined in this grant will increase our understanding of digestive processes in crustaceans and should be of relevance for determining optimal culture conditions for aquaculture or fisheries resource managers.