INTEGRATION OF PHYSIOLOGICAL-RESPONSES OF CRUSTACEANS TO ENVIRONMENTAL CHALLENGE

Brachyuran crustaceans are useful models for physiological studies bec ause of their intermediate size and since they occupy a spectrum of ha bitats requiring widely varied behaviour. In this paper we examine the physiological responses to environmental fluctuations, extremes of ha bitat and consequent behaviours, with special emphasis on the adoption of air-breathing. It is established that metabolic end products such as lactate, intermediates including urate, and monoamine and peptide n eurohormones can have important regulatory roles. These include effect s on ventilation and heart function, blood perfusion, respiratory gas transport, as well as water and salt homeostasis providing an integrat ed suite of control mechanisms to regulate responses to environmental or behaviourally induced stress. A separate body of work has long sugg ested that the regulation of energy metabolism and provision of metabo lic fuel for glycolysis is influenced by similar effecters. Most recen tly, metabolic end-products have been implicated as effecters of behav iour and thereby metabolic state. Thus, there is strong, emerging evid ence for integration of physiological control mechanisms at the organi smal level. We present new information, both mechanistic and from eco- physiological laboratory simulations, and from field studies of terres trial crabs, that strengthens and extends the scope of this integratio n. Branchial chamber ventilation, cardiovascular function, relative pe rfusion of gills v. lungs, gas transport in the blood, the mobilisatio n of energy reserves, ion transport and water balance are all apparent ly influenced by similar messengers which coordinate and optimise thes e functions to meet specific requirements.