Molecular phylogeny of Anomalodesmata (Mollusca: Bivalvia) inferred from 18S rRNA sequences

The origin of the anomalodesmatan bivalves and the relationships of the constituent families are far from being settled. Phylogenetic uncertainties result from the morphological heterogeneity of the Anomalodesmata and from parallel/convergent evolution of several character complexes due to similar life habits. Here, we assess these problems with 26 near-complete anomalodesmatan 18S rRNA sequences from 12 out of 15 families and a selection of heteroconch outgroup taxa. The robustly monophyletic Anomalodesmata share insertions in the V2 and V4 expansion regions. Both parsimony and maximum-likelihood analyses confirm their position among the basal heterodonts rooting between Carditidae and Lucinidae or, together with the latter, between Carditidae and the remaining Heterodonta. There is no support for monophyletic Myoida, nor for a close relationship of Anomalodesmata with any myoid taxon. At the base of the Anomalodesmata is an unstable cluster of long-branch species belonging to the Poromyidae, Verticordiidae, Lyonsiellidae and Thraciidae. The remaining Anomalodesmata split consistently but with varying branch support into three major clades: the Cuspidariidae excluding Myonera ; a 'thraciid' clade consisting of (Euciroidae, ( Myonera ( Thracia, Cleidothaerus , Myochamidae))); and a 'lyonsiid' clade with Laternulidae, Pandoridae, diphyletic Lyonsiidae due to a robust clade of Lyonsia norwegica and the clavagellid Brechites vaginiferus . Tests of various alternative topologies showed that all are significantly longer but optimal likelihood trees with monophyletic carnivorous taxa and/or Thraciidae are not significantly less likely. These results differ greatly from previous morphological studies. Palaeontological data and homology decisions for selected characters are evaluated in the light of the molecular trees.  © 2003 The Linnean Society of London, Zoological Journal of the Linnean Society , 2003, 139 , 229–246.     

Toxicity and repellency of Tephrosia candida to larval and adult Diaprepes root weevil (Coleoptera: Curculionidae)

Leaves of the tropical legume Tephrosia candida DC deterred feeding by adults of the Diaprepes root weevil, Diaprepes abbreviatus (L.), compared with leaves of Citrus macrophylla Wester, a common citrus rootstock, or T. vogelii Hook. f. When larvae were placed in pots containing plants of the three species for 28 d in a growth chamber, larval survival and weight gain were significantly reduced in pots containing plants of T. candida compared with larvae in pots with C. macrophylla or T. vogelii. Diet incorporation of lyophilized roots of T. candida into an artificial diet increasingly inhibited the growth of larvae and increased larval mortality with increased concentration of roots, whereas roots from C. macrophylla or T. vogelii had no effect compared with the diet-only control. T. candida, but not T. vogelii, contains at least one constituent that acts as an antifeedant toward adult D. abbreviatus and as a toxicant toward larvae. No antifeedant effect of roots of T. candida toward larvae was observed in no-choice pot tests or in a diet incorporation bioassay. In pots, larval feeding damage to roots of T. candida was evident. In the diet incorporation assay, 97% of larvae survived 29 d on a diet of cellulose powder (a nutritionally inert filler) despite losing weight. We conclude that decreased survival and weight gain of larvae-fed fresh or lyophilized roots of T. candida were the result of ingestion of a toxicant and not deterrence from feeding.     

THE FUNCTIONAL MORPHOLOGY OF THE ANTARCTIC BIVALVE THRACIA MERIDIONALIS SMITH, 1885 (ANOMALODESMATA: THRACIIDAE)

The functional morphology of the Thraciidae is poorly understood.Although some morphological aspects of several members havebeen described, only Trigonothracia jinxingae from Chinese watersis known in detail. Thracia meridionalis is the only representativeof the family in Antarctic waters, and is common in AdmiraltyBay, King George Island, where it inhabits muddy sediments.Thracia meridionalis shares many features with Tr. jinxingaethat are typical of most Anomalodesmata, i.e. a secondary ‘ligament’of thickened periostracum, extensively fused mantle margins,ctenidia of type E, a ctenidial-labial palp junction of categoryIII, a stomach of type IV and simultaneous hermaphroditism.Thracia meridionalis is, however, strikingly different fromTr. jinxingae in a number of ways, such as the presence of afourth pallial aperture, statocysts of type B₃, heterorhabdicctenidia, direct communication between the mantle chambers,a deep-burrowing habit (individuals lying on the left shellvalve), siphons that retract into mucus-lined burrows, a stomachwith extensive sorting areas, a rectum which passes over thekidneys and separate male and female gonadial apertures. Thereis, therefore, a greater range of morphological diversity withinthe Thraciidae than previously suspected. (Received 27 April 2004; accepted 30 November 2004)     

Reconstructing the Anomalodesmata (Mollusca: Bivalvia): morphology and molecules

The extant anomalodesmatan bivalves have always proved rather enigmatic and difficult to interpret, both in terms of their relationships to other bivalve taxa and the interrelationships of the constituent families. These difficulties stem from their diverse and often highly specialized life habits which have resulted in a wide array of disparate morphologies, and also from the fact that many are extremely rare. Classifications based on morphological characters have been dogged by fears that convergent and parallel evolution has masked phylogenetic signals. Molecular surveys of members of 12 of the 15 constituent families, using the 18S rRNA gene, have revealed that anomalodesmatans are robustly monophyletic and lie within the basal heterodonts. The Anomalodesmata should no longer be regarded as a subclass, but as a part of the Heterodonta. Here we present an enhanced analysis of 32 anomalodesmatan species (representatives of 12 families). Our results, subjected to Maximum Parsimony, Maximum Likelihood and Bayesian analyses, challenge our understanding of the internal relationships within the Anomalodesmata. In particular they indicate the need for a re-distribution of the families traditionally placed in the Thracioidea and Pandoroidea into a 'thraciid' lineage (Thraciidae + Cleidothaeridae + Myochamidae) and a 'lyonsiid' lineage (polyphyletic Lyonsiidae + Clavagellidae + Laternulidae + Pandoridae). The endolithic Clavagella and endobenthic Brechites and Penicillus form a robust clade. The hypothesis that the carnivorous septibranchs are monophyletic can, thus far, be neither supported nor rejected. Mapping critical morphological characters onto our molecular results provides evidence of multiple loss of some characters (e.g. prismato-nacreous shell microstructure and shell spicules) and also multiple gain of others (e.g. chondrophores).  © 2006 The Linnean Society of London, Zoological Journal of the Linnean Society , 2006, 148 , 395–420.     

Dynamic changes in prey choice by stickleback during simultaneous encounter with large prey

When a three-spined stickleback Gasterosteus aculeatus encountered prey simultaneously the probability of hanging and the median pursuit time were greater than when prey were encountered sequentially. During simultaneous prey encounter fish did not choose to attack the more profitable prey but instead the nearer prey was handled first except when the difference between the two prey sizes was large. No difference was found in the level of total energetic intake by the fish regardless of prey size pairing. Fish that handled and ate the first prey of a pair in <5 s attacked the second prey with a high probability of success, demonstrating an opportunistic feeding strategy. Importantly however, the fish did not choose to maximize long term energy intake rate by eating both prey, but rather short-term considerations over the course of feeding took precedence. With an empty stomach, the probability of a fish eating ( P _eat) the first prey handled was high regardless of prey size. As stomach fullness increased, the P _eat the first prey handled decreased if it was the larger prey. Hence, the fish were unselective when the stomach was empty but thereafter there was a shift in preference towards the smaller prey. The decision of which prey to attack and eat appeared to be based on short-term energy considerations and the level of stomach fullness. This study demonstrates that feeding on a short-term scale is a crucial factor to take account of when analysing fish feeding during simultaneous prey encounter.     

Helminth position within the intestine of naturally infected pike (Esox lucius) relative to host stomach contents

The positions of 3 cestode species, Triaenophorus crassus Forel, Triaenophorus nodulosus (Pallas), and Proteocephalus pinguis LaRue, and a nematode, Raphidascaris acus (Bloch), within the intestine of naturally infected pike (Esox lucius L.) were evaluated with respect to the presence or absence and state of digestion of host stomach contents. The positions of scolices and strobilae of the cestodes did not vary with respect to host stomach contents. By contrast, R. acus was anterior (near the stomach) when the stomach contained partially digested items, posterior when the stomach was empty, and in an intermediate position when the stomach contained only intact items. These results are interpreted as migration of R. acus, but not T. crassus, T. nodulosus, or P. pinguis, in response to feeding activity of the host. Adult and larval R. acus migrated, but the extent of migration was reduced in hosts harboring T. crassus, more so for larval than adult R. acus.     

Feeding biology of the Antarctic brittle star Ophionotus victoriae (Echinodermata: Ophiuroidea)

Summary The diet and feeding behavior of the brittle star Ophionotus victoriae were studied in 1981–1983. Frequency-of-occurrence and points methods were used to examine stomach contents of 2475 specimens from 19 stations representing seven general localities along the Antarctic Peninsula and South Sandwich Islands. Results of the two methods were in agreement and indicated this species is an opportunistic generalist with high diet plasticity. The most abundant component of the stomach contents was sediment but the diet derived from at least 13 phyla. Crustaceans, notably euphausiids and amphipods, were most important at some locations. Diet composition varied significantly between locations and years, but did not differ among brittle star size groups. Stomach content data and laboratory studies indicate that O. victoriae utilizes a variety of feeding methods but not suspension feeding.     

Hindlimb suspension and hind foot reversal in Varecia variegata and other arboreal mammals

The foot, perhaps more than any other region of the primate body, reflects the interaction of positional behaviors with the geometric properties of available supports. The ability to reverse the hind foot during hindlimb suspension while hanging from a horizontal support or descending a large diameter vertical trunk has been noted in many arboreal mammals, including primates. Observations of Varecia variegata in the wild and under seminatural conditions document hindlimb suspension in this lemurid primate. The kinematics and skeletal correlates of this behavior are examined. Analogy is made with the form and function exhibited by nonprimate mammalian taxa employing this behavior. Examples of carnivores and rodents display very similar adaptations of the tarsals while other mammals, such as the xenarthrans, accomplish a similar end by means of different morphologies. However, a suite of features is identified that is shared by mammals capable of hind foot reversal. Hindlimb suspension effectively increases the potential feeding space available to a foraging mammal and represents a significant, and often unrecognized, alternative adaptive strategy to forelimb suspension and prehensile-tail suspension in primates. Am J Phys Anthropol 103:85–102, 1997. © 1997 Wiley-Liss, Inc.     

The functional morphology of Propeamussium lucidum (Bivalvia: Pectinacea), a deep-sea predatory scallop

The abyssal propeamussiid Propeamussium is well known from studies of shell structure and is believed to be representative of a relict lineage, sister to the group which gave rise to all shallow-water pectinaceans.
From analyses of stomach contents, species of Propeamussium have been reported to be predators. This study confirms this and shows that small meiobenthos or epibenthic planktonic larvae and crustaceans constitute the diet. Prey is thought to be caught by an inrush of water to the mantle cavity and pushed into the mouth with the foot. The stomach is small, secondarily simplified and adapted for the digestion of small creatures. It is convergent with the stomachs of similarly predatory, abyssal anomalodesmatans. Palps are vestigial. The ctenidia are of a new type (B(4)), perhaps derivable from the dimyid ctenidium by the loss of the ascending lamellae of all four demibranchs and the ventral fusion of inner and outer descending lamellae on each side of the body to create a gill where the apices of the filaments are internal. Filter feeding is thus impossible, the ctenidia now wholly subserving a respiratory function.
Aspects of shell structure, adductor muscle arrangement and form of the pallial margin suggest that P. lucidum is a proficient swimmer. It is concluded, however, that prey is not caught during swimming, and that the two activities are mutually incompatible. Probably swimming is used only for escape.
Ctenidial structure forges links with the Plicatulacea (Dimyidae, Plicatulidae), shell structure with the Pectinacea (Pectinidae, Spondylidae) and it is concluded that the Propeamussiidae is indeed a relict group with links back to more primitive plicatulaceans and with the modern shallow-water Pectinacea, but evolving, in the isolation of the abyss, remarkable adaptations for a predatory mode of life. The Propeamussiidae also demonstrate striking convergence with the abyssal predatory Anomalodesmata.     

Suspension feeding and kleptoparasitism within the genus Trichotropis (Gastropoda: Capulidae)

The marine gastropod Trichotropis cancellata is a facultativekleptoparasite, either suspension feeding or parasitically stealingfood from tube-dwelling polychaete worms. To determine whetherconclusions drawn from long-term studies in the San Juan Islands,Washington, about the relative importance of suspension feedingand kleptoparasitism can be applied generally to T. cancellataacross its biogeographic range, I expanded earlier studies toAlaska and British Columbia. Kleptoparasitism is pervasive throughoutthe range of T. cancellata, occurring with equal frequency throughoutthe areas studied. The average density and size of worm hostsare relatively constant across this range. Snail and worm densitiesare not significantly correlated at the larger scale of site(averaged over nearby sampling locations clustered around acity), but are correlated at the smaller local scale (withina sampling location). Larger worms do not support more snails.The abundance of uninfected worm hosts is usually not limiting,except potentially in some sampling locations in southwest Alaskawhere the use of a novel host (a holothurian) may be the resultof low densities of uninfected worms. Additionally, I documentedthe feeding behaviours of other trichotropid species in theseregions. Trichotropis conica is the second confirmed kleptoparasitewithin the genus Trichotropis, with kleptoparasitism as frequentin this species as in T. cancellata. Like T. cancellata, allsizes observed of T. conica are kleptoparasites. On the otherhand, Trichotropis insignis is an obligate suspension feeder.Further studies are needed to determine exactly how many timesthis behaviour has arisen and been lost in Capulidae and relatedfamilies. (Received 31 May 2007; accepted 19 October 2007)     

Trehalose mediated growth inhibition of Arabidopsis seedlings is due to trehalose-6-phosphate accumulation

Trehalose-6-phosphate (T6P) is required for carbon utilization during Arabidopsis development, and its absence is embryo lethal. Here we show that T6P accumulation inhibits seedling growth. Wild-type seedlings grown on 100 mm trehalose rapidly accumulate T6P and stop growing, but seedlings expressing Escherichia coli trehalose phosphate hydrolase develop normally on such medium. T6P accumulation likely results from much-reduced T6P dephosphorylation when trehalose levels are high. Metabolizable sugars added to trehalose medium rescue T6P inhibition of growth. In addition, Suc feeding leads to a progressive increase in T6P concentrations, suggesting that T6P control over carbon utilization is related to available carbon for growth. Expression analysis of genes from the Arabidopsis trehalose metabolism further supports this: Suc rapidly induces expression of trehalose phosphate synthase homolog AtTPS5 to high levels. In contrast, T6P accumulation after feeding trehalose in the absence of available carbon induces repression of genes encoding T6P synthases and expression of T6P phosphatases. To identify processes controlled by T6P, we clustered expression profile data from seedlings with altered T6P content. T6P levels correlate with expression of a specific set of genes, including the S6 ribosomal kinase ATPK19, independently of carbon status. Interestingly, Suc addition represses 15 of these genes, one of which is AtKIN11, encoding a Sucrose Non Fermenting 1 (SNF1)-related kinase known to play a role in Suc utilization.     

Regulation of synthesis of GTP-cyclohydrolase participating in yeast falvinogenesis by iron

Pichia guilliermondii, Schwanniomyces occidentalis, Torulopsis candida and several riboflavin-dependent mutants of Torulopsis candida were grown in a medium with a low concentration of iron. In these conditions, the activity of GTP-cyclohydrolase which catalyzes the first step of flavinogenesis increases. The activity of the enzyme increases also when the cells of T. candida and P. guilliermondii with a high content of iron are incubated with alpha, alpha'-dipyridyl which induces overproduction of riboflavin; this action of alpha, alpha'-dipyridyl is eliminated by cycloheximide. Therefore, iron deficiency in the cells of these yeasts causes derepression of GTP-cyclohydrolase participating in riboflavin biosynthesis. The activity of the enzyme is inhibited by FAD but not by FMN and riboflavin.     

人工集鱼装置对热带金枪鱼类摄食模式的影响研究进展

热带金枪鱼类具有聚集在漂浮物体周围的行为特性,形成的集群表现稳定,可捕性较高。以此特性,金枪鱼围网渔业研制并投放了大量的人工集鱼装置(Fish Aggregation Device,FAD)用于聚集并捕捞金枪鱼。然而,大规模出现的FAD会使某些海域海面漂浮物的密度迅速增加,从而在一定程度上人为地改变了金枪鱼的表层栖息环境,对金枪鱼种群具有一系列可能的潜在负面影响,摄食模式的改变就是其中之一。归纳并综合了近年来国内外关于FAD对金枪鱼类摄食模式影响的相关研究,从摄食行为、日摄食量、饵料种类与组成以及生态位宽度4个方面对比了随附于FAD的金枪鱼和自由状态下同类的不同,发现大多情况下FAD的存在会使金枪鱼的摄食模式发生一定的改变。最后,归纳了过往实验存在的不足,对今后研究的发展方向进行了展望。     

Avian daily foraging patterns: Effects of digestive constraints and variability

Summary Birds show a typical daily pattern of heavy morning and secondary afternoon feeding. We investigate the pattern of foraging by a bird that results in the lowest long-term rate of mortality. We assume the following: mortality is the sum of starvation and predation. The bird is characterized by two state variables, its energy reserves and the amount of food in its stomach. Starvation occurs during the day if the bird's reserves fall to zero. The bird starves during the night if the total energy stored in reserves and the stomach is less than a critical amount. The probability that the bird is killed by a predator is higher if the bird is foraging than if it is resting. Furthermore, the predation risk while foraging increases with the bird's mass. From these assumptions, we use dynamic programming techniques to find the daily foraging routine that minimizes mortality. The principal results are (1) Variability in food finding leads to routines with feeding concentrated early in the day, (2) digestive constraints cause feeding to be spread more evenly through the day, (3) even under fairly severe digestive constraints, the stomach is generally not full and (4) optimal fat reserve levels are higher in more variable environments and under digestive constraints. This model suggests that the characteristic daily feeding pattern of small birds is not due to digestive constraints but is greatly influenced by environmental variability.     

Passive flow through an unstalked intertidal ascidian: orientation and morphology enhance suspension feeding in Pyura stolonifera

Passive flow is believed to increase the gains and reduce the costs of active suspension feeding. We used a mixture of field and laboratory experiments to evaluate whether the unstalked intertidal ascidian Pyura stolonifera exploits passive flow. We predicted that its orientation to prevailing currents and the arrangement of its siphons would induce passive flow due to dynamic pressure at the inhalant siphon, as well as by the Bernoulli effect or viscous entrainment associated with different fluid velocities at each siphon, or by both mechanisms. The orientation of P. stolonifera at several locations along the Sydney-Illawarra coast (Australia) covering a wide range of wave exposures was nonrandom and revealed that the ascidians were consistently oriented with their inhalant siphons directed into the waves or backwash. Flume experiments using wax models demonstrated that the arrangement of the siphons could induce passive flow and that passive flow was greatest when the inhalant siphon was oriented into the flow. Field experiments using transplanted animals confirmed that such an orientation resulted in ascidians gaining food at greater rates, as measured by fecal production, than when oriented perpendicular to the wave direction. We conclude that P. stolonifera enhances suspension feeding by inducing passive flow and is, therefore, a facultatively active suspension feeder. Furthermore, we argue that it is likely that many other active suspension feeders utilize passive flow and, therefore, measurements of their clearance rates should be made under appropriate conditions of flow to gain ecologically relevant results.     

Feeding performance of Lake Victoria rock cichlids: testing predictions from morphology

Cichlid fishes that seem specialized phenotypically to exploit certain resources often act as generalists in the field. It is attempted to resolve this paradox by measuring feeding performance. There are two ways of feeding, namely suction feeding and biting, that set conflicitng demands on the anatomy. Rock-dwelling cichlids of the genus Neochromis are specialized biters, feeding largely on filamentous algae and benthic organisms. Pundamilia nyererei is one of the most specialized suction feeders among rock cichlids, its diet being zooplankton and insect larvae. A morphological analysis showed that the three Neochromis species are better adapted anatomically to biting than P. nyererei , while P. nyererei is better adapted to suction feeding. Feeding performance was tested on algal substitute and Chaoborus larvae, representing filamentous algae and zooplankton, respectively. As expected the Neochromis species fed most efficiently on algal substitute, N. rufocaudalis and N. omnicaeruleus taking per bite 2.6 times as much as P. nyererei , and N. greenwoodi 1.7 times. Unexpectedly, the species examined were all well able to collect Chaoborus. P. nyererei collected only 1.2 times as many larvae per suction act as the Neochromis species. Analysis of the stomach contents showed that P. nyererei punctured, or lacerated, the larvae with the pharyngeal jaws, while the Neochromis species swallowed them mostly intact. Thus, feeding on Chaoborus , P. nyererei may be optimizing energy gain and not intake rate.     

These squatters are not innocent: the evidence of parasitism in sponge-inhabiting shrimps

Marine sponges are frequently inhabited by a wide range of associated invertebrates, including caridean shrimps. Symbiotic shrimps are often considered to be commensals; however, in most cases, the relationship with sponge hosts remains unclear. Here we demonstrate that sponge-inhabiting shrimps are often parasites adapted to consumption of sponge tissues. First, we provide detailed examination of morphology and stomach contents of Typton carneus (Decapoda: Palaemonidae: Pontoniinae), a West Atlantic tropical shrimp living in fire sponges of the genus Tedania. Remarkable shear-like claws of T. carneus show evidence of intensive shearing, likely the result of crushing siliceous sponge spicules. Examination of stomach contents revealed that the host sponge tissue is a major source of food for T. carneus. A parasitic mode of life is also reflected in adaptations of mouth appendages, in the reproduction strategy, and in apparent sequestration of host pigments by shrimp. Consistent results were obtained also for congeneric species T. distinctus (Western Atlantic) and T. spongicola (Mediterranean). The distribution of shrimps among sponge hosts (mostly solitary individuals or heterosexual pairs) suggests that Typton shrimps actively prevent colonisation of their sponge by additional conspecifics, thus protecting their resource and reducing the damage to the hosts. We also demonstrate feeding on host tissues by sponge-associated shrimps of the genera Onycocaris, Periclimenaeus, and Thaumastocaris (Pontoniinae) and Synalpheus (Alpheidae). The parasitic mode of life appears to be widely distributed among sponge-inhabiting shrimps. However, it is possible that under some circumstances, the shrimps provide a service to the host sponge by preventing a penetration by potentially more damaging associated animals. The overall nature of interspecific shrimp-sponge relationships thus warrants further investigation.     

Feeding Ecology of Northeast Atlantic Mackerel,Norwegian Spring-Spawning Herring and Blue Whiting in the Norwegian Sea

The Norwegian spring-spawning (NSS) herring (Clupea harengus), blue whiting (Micromesistius poutassou) and Northeast Atlantic (NEA) mackerel (Scomber scombrus) are extremely abundant pelagic planktivores that feed in the Norwegian Sea (NS) during spring and summer. This study investigated the feeding ecology and diet composition of these commercially important fish stocks on the basis of biological data, including an extensive set of stomach samples in combination with hydrographical data, zooplankton samples and acoustic abundance data from 12 stock monitoring surveys carried out in 2005–2010. Mackerel were absent during the spring, but had generally high feeding overlap with herring in the summer, with a diet mainly based on calanoid copepods, especially Calanus finmarchicus, as well as a similar diet width. Stomach fullness in herring diminished from spring to summer and feeding incidence was lower than that of mackerel in summer. However, stomach fullness did not differ between the two species, indicating that herring maintain an equally efficient pattern of feeding as mackerel in summer, but on a diet that is less dominated by copepods and is more reliant on larger prey. Blue whiting tended to have a low dietary overlap with mackerel and herring, with larger prey such as euphausiids and amphipods dominating, and stomach fullness and feeding incidence increasing with length. For all the species, feeding incidence increased with decreasing temperature, and for mackerel so did stomach fullness, indicating that feeding activity is highest in areas associated with colder water masses. Significant annual effects on diet composition and feeding-related variables suggested that the three species are able to adapt to different food and environmental conditions. These annual effects are likely to have an important impact on the predation pressure on different plankton groups and the carrying capacity of individual systems, and emphasise the importance of regular monitoring of pelagic fish diets.     

Autometallographical localisation of Cu and Zn within target cell compartments of winkles following exposure to Cu&Zn mixtures

This investigation attempts to determine the usefulness of autometallography to localise particular metals in certain key tissues of molluscs exposed to metal mixtures. For this purpose, winkles (Littorina littorea) removed from shell were exposed to very high concentrations of either copper (Cu), zinc (Zn) or a mixture of both metals (Cu&Zn) dissolved in sea-water for short periods of time. Protein-bound metals were detected by autometallography as black silver deposits (BSD) on histological sections of gills, foot, mantle, digestive gland/gonad complex, stomach and kidney. Copper was localised within cytoplasmic granules of gill ciliated cells, nephrocytes and stomach epithelial cells as well as within digestive cell lysosomes. Zinc was essentially found in the basal lamina (histological sense) of gill, stomach, kidney and digestive gland epithelia. BSD were also evidenced in cytoplasmic granules of pore cells present in parenchymal connective tissue of mantle, foot, gill, digestive gland and stomach. Copper and zinc concentrations were additionally calculated for the whole soft body as well as for certain organs by atomic absorption spectrophotometry (AAS). According to AAS, a synergistic phenomenon would contribute to increase the rate of Cu and Zn accumulation in presence of each other. However, after exposure to Cu&Zn autometallography did not evidence any synergistic phenomenon, and Cu and Zn were localised in their respective accumulation sites. In conclusion, autometallography might indicate the presence of certain metals in the environment irrespective of factors, such as "metal-metal interaction-like" phenomena, affecting metal concentrations in soft tissues.     

Ghrelin and body weight regulation in the obese Zucker rat in relation to feeding state and dark/light cycle

Ghrelin is a new orexigenic peptide primarily produced by the stomach but also present in the hypothalamus. It has adipogenic effects when it is chronically injected in rodents but in obese humans, its plasma concentration is decreased. It can reverse the anorectic effects of leptin when it is co-injected with this peptide in the brain ventricles. The Zucker fa/fa rat is a genetic model of obesity related to a default in the leptin receptor. It is characterized by a large dysregulation of numerous hypothalamic peptides but the ghrelin status of this rat has not yet been determined. Through several experiments, we determine in lean and obese Zucker rats its circulating form in the plasma, its tissue levels and/or expression, and studied the influence of different feeding conditions and its light/dark variations. Ghrelin expression was higher in the obese stomach and hypothalamus (P < 0.05 and P < 0.02, respectively). The ratio of [Octanoyl-Ser3]-ghrelin (active form) to [Des-Octanoyl-Ser3]-ghrelin (inactive form) was approximately 1:1 in the stomach and 2:1 in the plasma in lean and obese rats (no differences). After fasting, plasma ghrelin concentrations increased significantly in lean (+ 64%; P < 0.001) and obese (+ 60%; P < 0.02) rats. After 24 hours of refeeding, they returned to their initial ad lib levels. Ghrelin concentrations were higher in obese rats by 69% (P < 0.005), 65% (P < 0.02), and 73% (P < 0.005) in the ad libitum, fast, and refed states respectively. These results indicate that the obese Zucker rat is characterized by increases in the stomach mRNA expression and in peptide release in the circulation. They clearly support a role for ghrelin in the development of obesity in the absence of leptin signaling.