Neurosecretion and Salt and Water Balance in the Annelida and Crustacea

The possible role of the neurosecretory system in regulationof salt and water has been studied in the annelids and crustaceans.In the earthworm, Lumbricus terrestris, a brain factor influences'the salt and osmotic concentration of the blood and coelomicfluid. Removal of the brain results in the increase of waterinflux with a decrease in the salt and osmotic concentrationsof the body fluids. The decreases in salt and osmotic concentrationscan be prevented by the implantation of the brain or the injectionof brain homogenates. In the freshwater crayfish, Procambarus clarkii, a factor, presumablysecreted in the brain and released in the eyestalk, seems tomaintain the normal permeability of the body surfaces to water.Eyestalk removal, which eliminates the release site, resultsin the increased influx of water with a decrease in the saltconcentration of the blood. A brain factor also seems to beinvolved in maintaining the sodium and osmotic concentrationsof the blood. In the semi-terrestrial grapsid crab, Metopograpsus messor,the thoracic ganglion, under the control of an eyestalk element,secretes a factor involved in increasing the permeability ofthe body surfaces to water. The removal of the eyestalks, theimplantation of the thoracic ganglion, or the injection of extractsof thoracic ganglia, results in changes in the osmotic concentrationof the blood tending toward that of the medium. In all threespecies studied, the neuroendocrine factors seem to be involvedprimarily in the regulation of the permeability of the bodysurfaces to water.     

Diversity of Cenozoic marsupiate echinoids as an environmental indicator

McNamara, K.J. 1994 10 15: Diversity of Cenozoic marsupiate echinoids as an environmental indicator. Marsupiate echinoids are today largely confined to the seas around Antarctica. Consequently, it has often been inferred that the presence of marsupiate echinoids in the fossil record is indicative of the former existence of low oceanic temperatures. In this study the distribution of marsupiate echinoids through the Cenozoic succession of southern Australia is compared with palaeo-temperature data to test this assumption. The analysis reveals that there is no positive correlation between high marsupiate echinoid diversity during the Cenozoic and low oceanic temperatures. An alternative hypothesis, based on life-history strategies, is investigated. This reveals that marsupiate echinoids show many characteristics typical of organisms with slow growth, long life spans and production of few, large offspring. It is suggested that the northward migration of Australia during the Cenozoic from an original high-latitude location in the early Cenozoic was accompanied by an increase in environmental instability in the southern Australian region in the late Cenozoic. This led to a consequent decrease in marsupiate echinoid diversity. During the Pliocene these direct brooding echinoids were replaced by non-brooders with pelagic lecithotrophic larvae, which dominate the southern coastal echinoid fauna of Australia today. The environmental stability experienced in southern Australia in the early Cenozoic persisted throughout the Cenozoic in the Antarctic region, particularly with regard to predictability of nutrient supply. The result has been the dominance of marsupiate echinoids in that region today. Temporal changes in the diversity of marsupiate echinoids in southern Australia therefore supports the view that their spatial and temporal distribution may be more closely correlated with aspects of their life-history strategy and environmental stability than with low temperature. Echinoidea, evolution, diversity, life-history strategy, Cenozoic.     

Morphology and aestivation behaviour in some Madagascan acavid land snails

Nine species of Madagascan acavid land snails were compared in a phylogenetic context. The two most plesiomorphic, Clauator johnsoni and C. moreleti, differ from the others by their high-spired shells, short tentacles, short tails, long necks, and crawling mode of hitching the shell along the ground. In the seven more apomorphic species, the crawling mode is smooth, with the shell resting on the tail, and the relative lengths of tail and shell correlate significantly. Among these seven species, three pairs of closest relatives (Helicophanta petiti and H. uesicalis, H. farafanga and H. souuerbiana, Ampeltta decaryi and A. julii) show evidence of phylogenetic constraints on ranked shell size. Aestivation site (as tentatively inferred from rare data) does not correlate with shell shape or size: burrowers have H/D = 2.7 to 0.6 and D = 70 to 25 mm; arboreals have H/D = 0.8 to 0.5 and D = 70 to 30 mm; the species with both the highest spire and the smallest diameter (C. moreleti) is neither a burrower or an arboreal, but stays on the ground surface. Inferred aestivation sites are randomly distributed phylogenetically. Climate shows no correlation, except that the arborcals are only from humid to wet regimes. Uniform shell colouration occurs only in burrowers (C. johnsoni, H. petiti, H. uestcalis), but disruptive shell colouration occurs in all others, including burrowers (H. farafanga, A. decaryt), ground-surface aestivators (C. moreleti), arboreals (H. souuerbiana, A. julii), and semi-arboreals (Ampefita subfunebris). Among all nine species, burrowers have significantly thicker shells (than their close relatives of similar size), wider bodies, and longer snouts than non-burrowers (H. souuerbiana is exceptional in being arboreal despite its huge size and in having the broad foot and snout of a burrower). Thus, although there is some evidence for phylogenetic constraints, natural selection for aestivation and crawling behaviours seems to have dominated the evolution of external body morphology and of shell thickness (but not shell size and shape) in these snails.     

Biodiversity of Coral Reefs: What are We Losing and Why?

SYNOPSIS. Coral reefs are threatened by numerous anthropogenicimpacts, some of which have already had major effects worldwide.These unique tropical environments harbor a high diversity ofcorals, reef invertebrates, fish and other animals and plants.In most taxa, the species diversity of reef-associated organismsis poorly understood because many of the species have yet tobe collected and described. High coral mortality has been associatedwith natural events such as hurricanes, predator outbreaks andperiods of high temperature, but has also resulted from excessnutrients in sewage and from specific pollutants. Reef coralsand associated organisms are also threatened by the possibilityof global warming which will result in rising sea levels andperiods of increased temperature stress, and which may alsobring increased storm frequency and intensity. Although therecent extensive episodes of coral bleaching in the Caribbeanand eastern Pacific cannot be causally related to global warmingat this time, the close link between bleaching and temperaturesuggests that global warming will result in severe changes incoral assemblages. Major reef destruction has followed outbreaksof the predatory seastar Acanthaster planci in the Pacific.Although this is considered part of a natural disturbance cycle,there are indications that altered land use patterns and reductionof predators on this seastar by human activities may have increasedthe severity of outbreaks. Recreational and commercial use ofreefs has also increased, and has caused extensive damage, especiallynear areas of high population density. One of the most obviousand widespread losses to reef biota is the reduction in fishpopulations from intense overfishing in most reef areas of theworld. Coasts without adequately managed reefs have sufferedintense overfishing for both local and export purposes, to thepoint where the positive effects of fish on those reefs havebeen compromised. The combination of these destructive factorshas altered reefs in all localities, and many that were onceconsidered protected by distance and low population densityare now being exploited as well. On the positive side, improvedunderstanding of ecological processes on reefs combined withconcerted conservation efforts have managed to protect someextensive areas of reef for the future.     

Coelenterate Neuropeptides: Structure, Action and Biosynthesis

Evolutionary "old" nervous systems such as those of coelenteratesare peptidergic: Using various radioimmunoassays we have nowisolated 13 novel neuropeptides from sea anemones and severalothers from hydrozoan polyps and medusae. These peptides areall structurally related and contain the C-terminal sequenceArg-X-NH₂ or Lys-X-NH₂, where X is Ala, Asn, Ile, Phe, Pro orTrp. Three neuropeptides have a novel N-terminal L-3-phenyllactylresidue, which protects against degradation by nonspecific aminopeptidases.The neuropeptides from sea anemones are produced by differentsets of neurones and have excitatory or inhibitory actions onisolated muscle preparations, suggesting that they are neurotransmittersor neuromodulators. We have also cloned the precursor proteinfor the sea-anemone neuropeptide Antho-RFamide (<Glu-Gly-Arg-Phe-NH₂).In Calliactis parasitica this precursor harbours 19 copies ofimmature Antho-RFamide (Gln-Gly-Arg-Phe-Gly) together with 7other, putative neuropeptide sequences. The precursor of Anthopleuraelegantissima contains 14 copies of Antho-RFamide and 19 other,putative neuropeptides. This shows that the biosynthetic machineryfor neuropeptides in coelenterates, the lowest animal grouphaving a nervous system, is already very efficient and similarto that of higher invertebrates, such as molluscs and insects,and vertebrates.     

Regulation of Protein Synthesis in Embryos of Ilyanassa obsoleta

Much of the protein synthesis during early development in Ilyanassaresults from the translation of oogenetic mRNA. We show thatmicrotubule proteins are products of this translation, and thattheir synthesis is subject to translation level regulation.We also show that translation level regulation is involved inthe function of the polar lobe by making comparisons of theelectrophoretic patterns of synthesis of ¹⁴C labeled proteinsof normal embryos with the patterns of synthesis of ³H labeledproteins of embryos from which the polar lobes had been removedat the trefoil stage. Controls utilizing biochemical and morphologicalmarkers were performed to assure that normal and delobed embryoswere developing at equivalent rates. The expression of significantdifferences in the patterns of protein synthesis were foundbetween normal and delobed embryos, and these differences werenot dependent upon concomitant RNA synthesis. These differenceswere observable as early as after only 24 hours of development,although organogenesis does not begin until much later in development.Therefore, the observed differences probably reflect determinativeevents. The results support the hypothesis that the developmentaldeterminants of the polar lobe may include specific, preformedmRNA sequences, or specific regulators of translation.