Neurohormonal Integration of Osmotic and Ionic Regulation

There is evidence in crustaceans that neuroendocrine centers,including the eyestalk, brain, thoracic ganglionic mass, andpericardial organ, produce factors that affect osmotic and ionicregulation. Understanding of the processes responsible for osmoticadjustment in the intact animal, such as regulation of permeability,active uptake of ions, and respiratory and cardiovascular alterations,has increased substantially in the past few years. However,interaction of neuroendocrine factors with the target tissuesand systems is just beginning to be investigated. There is evidencethat content of lipids and activity of enzymes are importantin osmoregulation, and neuroendocrine effects on these metabolicprocesses are worthy of study. In addition, there are some crustaceansin which osmoregulatory ability varies developmentally. Furtherinvestigations of such animals is also necessary. Progress inour understanding of neuroendocrine influences on osmoregulationdepends upon further purification of active factors from neuroendocrinecenters and hemolymph, and upon development of appropriate assayson which to test them.     

Adaptations of Crustaceans to Land: A Summary and Analysis of New Findings

Crustaceans have adapted to land through various morphological,physiological, biochemical, and behavioral modifications, ofwhich some are shared by all land-dwelling crustaceans and othersare unique to animals within a particular habitat. Among thethree groups of crustaceans having truly terrestrial members,the amphipods have achieved their success on land primarilyby behavioral means, while the isopods and the decapods havedeveloped many morphological, physiological, and biochemicaladaptations as well. In all three groups, behavioral modifications ensure that lossof water is minimal, that the animals are exposed to favorablerather than extreme environmental conditions, and that the fineline between evaporative cooling and excessive dehydration ismaintained. In most crustaceans the excretion of nitrogenous wastes requiresthat copious supplies of water be available for washing awaythe soluble end-products. Yet terrestrial isopods are able toexcrete ammonia as a gas, without being subject to toxic side-effects.In decapods, either ammonia or insoluble uric acid may be excreted,with ammonia the more likely product when water is available,uric acid when water is scarce. In adult land crabs water balance is maintained through theconcerted action of gills, pericardial sacs, and gut. Theseorgans may take up, store, and redistribute salts and waterin response to control exerted by the central nervous systemthrough its secretory products. In larvae of land crabs theseorgans are not known to function in this way. Rather, the larvaeare adapted to cope with osmotic problems of their planktonicexistence. Gaseous exchange in adult land crabs is carried on not onlyby the gills but also by the highly vascularized lining of thebranchial chambers, and the hemocyanin ot these crabs is adaptedto function in the environment peculiar to each species. Terrestrialcrabs seem unable to withstand low temperatures, but their highrate of cytochrome c oxidase activity may help them to survivewhen temperatures are high. Modifications in behavior must have occurred quite early inthe transition of crustaceans from sea to land. Then, as now,appropriate behavioral responses to light, temperatuie, humidity,tidal cycles, and so on. were crucial if a terrestrial animalwas to survive. Social interactions, both for courtship andfor aggression, required the sending and receiving of appropriatevisual and acoustic signals and were promoted by the ritualizationof potentially injurious patterns of behavior.     

Contributions of Dorothy M. Skinner to the Development of Crustacean Biology

Dorothy M. Skinner's interest in the study of crustaceans grewout of her experiences as a student and teaching assistant inthe Experimental Invertebrate Zoology course at the Marine BiologicalLaboratory, Woods Hole, MA. Her early training in both biologyand chemistry was instrumental in allowing her to pursue linesof research as diverse as control of molting and regeneration,structure of the crustacean integument, and characteristicsof satellite DNAs throughout her career. Dorothy published anumber of landmark papers in crustacean biology over the years,which served to inspire the work of numerous biologists. Thebreadth and depth of her contributions was made apparent inthis symposium, in which eleven researchers presented theirnewest findings in the areas of satellite DNA, control of regenerationand molting, dynamics of muscle atrophy and reorganization,and structure and evolution of arthropod proteins.     

The Foregut of Gecarcinus lateralis as an Organ of Salt and Water Balance

The permeability of the foregut of the land crab, Gecarcinuslateralis, to tritiated water (THO), Na²², and Cl³⁶ was studiedin vitro during the intermolt period and after ecdysis. In crabswith eyestalks, the foregut is permeable to water and ions inthe direction hemolymph-to-lumen and lumen-to-hemolymph, bothduring the intermolt period and after ecdysis. However, theforegut of animals without eyestalks is impermeable after ecdysis. The movement of THO always follows the movement of Na²² acrossthe wall of the foregut, while the movement of Cl³⁶ may or maynot be correlated with the movement of Na²² and THO. Comparisonof the ratio of water to ions in the hemolymph with the ratiocalculated from radioisotope flux indicates that Na⁺ and waterare probably moving isosmotically, although not necessarilyaccompanied by Cl^– When an extract of the thoracic ganglionic mass of G. lateralisis added to the "hemolymph side" of the foregut in vitro, thereis immediately a large increase in permeability to water andsalts. This occurs in the foregut of crabs with eyestalks duringintermolt and also in eyestalkless crabs after ecdysis. Thus, not only is the foregut of Gecarcinus lateralis permeableto water and salts in both directions, but also the extent ofits permeability is under neuroendocrine control. As a consequence,the animal may be able to move water and salts into the foregutor out of it into the hemolymph as needed. This may be an importantadaptation for a terrestrial crab that must conserve water,especially at the critical time of ecdysis.