Interacting Factors in the Control of the Crustacean Molt Cycle

In order to account for the known phenomena of the crustaceanmolt cycle, at least six factors must be postulated: a moltinghormone (20-OH-ecdysone), a molt-inhibiting hormone (MIH), ananecdysial limb autotomy factor, a proecdysial limb-autotomyfactor, a limb growth-inhibiting factor and an exuviation factor.Only the molting hormone and its derivatives have been chemicallywell defined. The various factors interact in complex ways tomaintain not only a coordinated proecdysial period in preparationfor exuviation but also a proecdysial period with the flexibilityto respond to such interim hazards as the loss of partiallyregenerated limbs.     

DIDYMELLA STEM-ROT OF OUTDOOR TOMATOES

In studies on Didymella stem-rot of outdoor tomatoes several possible modes of introduction of the disease were investigated, together with methods of avoiding them. The pathogen was found to invest and penetrate the seeds in diseased fruit without destroying their viability and methods were devised of ridding the seeds of infection. It was not, however, possible to demonstrate the infection of mature plants from infected seed. It was found that the disease could be introduced on contaminated canes, in potting soil and from plant debris from the previous season's crop. The spread of the disease was encouraged by overhead irrigation.
Tests of strains of various species of Lycopersicon showed that one line of L. hirsutum was highly resistant to stem and root infection although another line was highly susceptible.     

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.     

Rapid laying by Brown-headed Cowbirds Molothrus ater and other parasitic birds

We compared the length of time parasitic and nonparasitic female birds spent on nests while laying eggs (laying bouts) to evaluate the hypothesis that rapid laving by parasitic Brown-headed Cowbirds Molothrus ater and other parasitic birds is a specialization for brood parasitism. Brown-headed Cowbirds typically spent less than 1 min on host nests while laying (41.0 ± 4.58 [mean ± s.e.] s, n = 21). In contrast, mean laving bouts of six nonparasitic icterine species ranged from 21.5 min to 53.4 min, and laying bouts of 13 other passerine species ranged from 20.7 min to 103.7 min. By spending only a few seconds on the nest while laying, brood parasites probably increase their chances of parasitizing nests unnoticed by hosts or, if noticed, are harassed by hosts for less time. Rapid laying may be adaptive if aggression by hosts can thwart attempted parasitism by chasing away the parasite, preventing the parasite from entering the nest or injuring the parasite. Rapid laying may increase the likelihood that the parasitic egg will be accepted. We tested some of these hypotheses by recording the responses of three frequently parasitized species to a stuffed female cowbird placed on their nests for 1 min. All species attacked the model vigorously; however, the mean time for discovery of the model ranged from 3 min to 17 min, ample time for female cowbirds to parasitize the nests. We concluded that rapid laying by parasitic birds is an adaptation for parasitism and, in Brown-headed Cowbirds, reduces the chances that the parasite will be attacked by hosts.     

Proteins of the Crustacean Exoskeleton

We describe here some of the components of the exoskeleton ofthe decapod crustacean with emphasis on the constituent proteins,including both structural and enzymatic. All four layers, butparticularly the inner three, of the exoskeletons of four brachyuranscontain high concentrations of proteins 31 kDa; the innermostmembranous layer is especially rich in such proteins. A numberof crab exoskeletal proteins resemble insect cuticle proteinsin size (M_r) and isoelectric point (pI). A further similarityis the cross reactivity of crab exoskeletal proteins with fourdifferent antibodies against cuticular proteins of two speciesof insects. One of the small M_r exoskeletal proteins in theBermuda land crab Gecarcinus lateralis has a similar distributionas a protein of similar size in the cuticle of the tobacco hornworm Manduca sexta. The partial dissolution of an old exoskeletonand formation of the two outer layers of a new exoskeleton aremajor events in readying a crustacean for the increase in sizethat occurs at each molt. Expressing both parallel and sequentialactivation of a number of genes, a single layer of epidermalcells that bounds a crustacean such as G. lateralis synthesizesspecific proteins at different stages of the intermolt cycleas the outermost epicuticle and exocuticle are formed duringproecdysis and as the endocuticle and membranous layer are formedduring metecdysis. Finally, two sets of proteinases isolatedfrom integumentary tissues of land crabs degrade the same exoskeletalproteins in vitro as are degraded in vivo during proecdysis.     

Isoprenoid Quinone Composition as a Guide to the Classification of Sporolactobacillus and Possibly Related Bacteria

Menaquinones with seven isoprene units were the major isoprenoid quinones detected in the chloroform-methanol extracts of representative strains of the genera Bacillus and Sporolactobacillus. Neither menaquinones nor ubiquinones were detected in similar extracts of strains of the genus Lactobacillus.     

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.     

Ciliate Ultrastructure: Some Problems in Cell Biology*

SYNOPSIS. Protozoology, along with other cell sciences, has profited immeasurably during the last 25 years from the application of electron microscopy and other new technics to studies of cell structure and function. Protozoa were among the first objects examined with the electron microscope in the 1940's and an extensive literature in protozoan ultrastructure has accumulated since then. Some examples of recent investigations of ciliate cortical ultrastructure are selected to illustrate the importance of protozoan studies to the development of fundamental concepts of cell biology. Ciliates are choice subjects for analysis of ciliary structure and motility and of myoneme contractility. Membrane-limited alveoli contribute to the structure of the characteristic ciliate pellicle and provide evidence of how multiple pellicular membranes may affect cell-surface activities. The striated fibrils and microtubules associated with ciliate kinetosomes resemble those of other cell types but are more highly organized; wherever they occur, these structures appear to be related to the development and maintenance of polarity and asymmetry of cells and organelles. Their stability and the precision of their arrangement in ciliates make them peculiarly suitable for the study of the properties and behavior of such fibrous organelles and also for investigation of the morphogenetic role of the kinetosome.     

The effect of clipping on methane emissions from Carex

The purpose of this study was to estimate theresistance to methane release of the above-groundportion of Carex, a wetland sedge, and todetermine the locus of methane release from the plant. Measurements conducted on plants clipped to differentheights above the water level revealed that themethane flux from clipped plants was on the order of97% to 111% of control (unclipped) values. Thegreatest increase was observed in the initial fluxmeasurement after the plants had been clipped to aheight of 10 cm. Subsequent measurements on the 10 cmhigh stubble were similar to control values. When theends of plants which had been clipped to 10 cm weresealed, the methane flux was reduced to 65% ofcontrol values. However, sealing had no effect on theflux from plants which were clipped at 15 cm andhigher, indicating that virtually all methane wasreleased on the lower 15 cm of the plants as theyemerged from the water. The results indicate that theabove-ground portions of Carex at our studysite offered only slight resistance to the passage ofmethane, and that the main sites limiting methaneemission are below-ground, at either theporewater-root or root-shoot boundary. We hypothesizethat the transitory increase in flux associated withclipping was due to the episodic release of methaneheld within the plant lacunae. The buildup ofCH₄ partial pressure within lacunal spacesovercomes the resistance to gas transport offered byaboveground parts.