Water Balance in the Land Crab, Gecarcinus lateralis, During the Intermolt Cycle

Gecarcinus lateralis can take moisture from a clamp substratumin amounts adequate for the needs of the entire intermolt cycle.It can also rehydrate in this way, even after severe dehydration. This crab is able to survive for many months when free waterof a wide range of salinities (0.30; = parts per thousand)is made available in a shallow dish. The crab dies within sevenweeks when the salinity of this water is 35. During proecdysisthe pericardial sacs of eyestalkless crabs become most swollenwhen the salinity of the available water is 15 or 23, and survivalduring and after ecdysis is greatest with water of 15. A crab in proecdysis shows no increase in the rate at whichwater enters following dehydration. Yet large amounts of waterare retained, particularly at the intermediate salinities. Maximalswelling of the pericardial sacs just prior to ecdysis is essentiallyequivalent in crabs with eyestalks, in eyestalkless crabs, andin eyestalkless crabs that have received an implant of centralnervous tissue. Hence, we conclude that a hormone causing theretention of water exists, but not in the eyestalks, in thebrain, or in the thoracic ganglionic mass. At ecdysis eyestalkless crabs show large increases in the dimensionsof the carapace, while crabs with eyestalks and eyestalklesscrabs that have received an implant of certain central nervoustissues show much less increase and may even show a decrease.Thus, we conclude that a hormone causing a release of waterat ecdysis is produced in the central nervous system. The advantages to the crab of a dual hormonal control of itswater balance are discussed.     

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.     

From Sea to Tree: Saga of a Land Crab

There are advantages to be gained when an animal abandons itsancestral home, the ocean, and advances across the littoralzone to the land. But along with the advantages come the inevitableproblems. How a land crab, Gecarcinus lateralis, has solvedits problems of life on land is the subject of this paper. Itsuse of dew as a source of moisture and of its burrow as a refugefrom predators and a hostile environment; its ability to collectmoisture from a damp substrate and conduct this moisture toits branchial chambers and its gills; its capacity to retainlarge amounts of water before ecdysis and to use this waterto stretch its new soft exoskeleton and attain its proper shapeafter ecdysis are only a few of the crab's special adaptationsfor terrestrial life. Its feeding and reproductive behaviorare equally adaptive, as is its propensity for tree-climbingwhen danger threatens–or at other times. During the pastseveral decades, much interesting and important research hasbeen done on G. lateralis, as well as on other land crabs–butmuch remains to be done. Land crabs are and will undoubtedlycontinue to be promising objects of scientific research.     

The inhibitory effect of NaCl on barley germination

Abstract The possibility that the nature of the inhibitory effect of NaCl is different during imbibition compared to germination was investigated. Germination in both NaCl and betaine (a non-toxic solute) improved with pre-imbibition in water. Seeds imbibed in inhibitory concentrations of either solute could be induced to germinate by brief exposure to water. Electron micrographs of tissue from seeds imbibed in 0.5 kmol m^?3 NaCl for 25 h showed cells identical to those in seeds imbibed in water for only 1 h, but seeds imbibed for 6 h in water exhibited many changes in ultrastructure. These results are consistent with the hypothesis that seed hydration must reach a critical value before germination can proceed, and that the inhibitory effect of NaCl is primarily osmotic in barley seeds that have not reached this hydration threshold. Although isotonic solutions of betaine and NaCl were equally inhibitory to germination, isotonic solutions of betaine and NaCl were not equally inhibitory to continued development in seeds which had been pre-imbibed in water. Calcium ions improved both germination and plumule emergence of pre-imbibed seeds in NaCl solutions, but calcium had little effect on pre-imbibed seeds placed in betaine. Very high concentrations of NaCl or betaine inhibited germination, but did not kill dry seeds. Both solutes, on the other hand, were lethal at high concentrations to germinating seeds. NaCl killed germinating seeds more rapidly than betaine, but calcium reduced the rate of killing to nearly that of betaine. We conclude that hydrated seeds are sensitive to both osmotic and toxic effects of NaCl and that calcium mitigates the toxic effect of NaCl, but not the osmotic effect.     

Changes in plasmalemma organization in cowpea radicle during imbibition in water and NaCl solutions

Abstract Freeze-fracture electron microscopy of the plasmalemma of dry cowpea radicle cells disclosed a normal-appearing membrane with a high area density of intramembraneous particles (IMPs). Seeds imbibed in either water or salt solution exhibited decreased area density of IMPs, but water-imbibed tissue showed the greatest decline. Mean particle size increased with hydration but not enough to suggest aggregation as the cause for this density decrease. Calculations of plasmalemma area expansion during imbibition show that such expansion can account for the decrease in IMPs per unit area in the cytoplasmic side (PF) of the membrane in water-imbibed, but not in salt-imbibed, tissue. During imbibition, there is a change in the ratio of IMPs per unit area of the PF versus EF (external) membrane faces, suggesting a relative increase in the number of EF particles. These changes in membrane structure are probably not related to any decrease in membrane permeability during the early phases of imbibition.