Pan-tropical distribution of the Jurassic ostreid bivalves

Globally, the Jurassic cemented ostreid bivalves from northern Tibet, SW China, have a pan-tropical distribution pattern between palaeolatitudes of 60° South and North. Ostreid bivalves have tiny to large larvae, and nearly all of them have a cemented mode of life during their adult stage. The distribution pattern and the habits of the Jurassic ostreid bivalves revealed that, in the Jurassic time interval, all seas and oceans were interconnected, and ostreid bivalves were very capable of dispersion through their planktonic larval stage or as pseudoplankton during the post-larval stage, and even were able to cross the palaeo-Pacific Ocean from east to west. However, latitudinal temperature variation limited the distribution of these thermophilous bivalves to the lower and middle latitudes.     

Morphological Variability and Levels of Nuclear Ploidy in Neurons of the Central Nervous System of Bivalves Relative to the Problem of Somatic Polyploidy

Ploidy of neurons was assessed by the method of nuclear DNA cytophotometry in ganglia of the central nervous system (CNS) in 28 species of Bivalvia belonging to 5 existing subclasses and having various bio-ecological characteristics. A significant variation in the nucleus size and chromatin structure was revealed on crush preparations and slides; however, almost all nuclei were diploid. Some species had nuclei with tetraploid DNA value (from 0.2 up to 1%) and with condensed chromosomes, the probable mitotic fraction of cells. It was concluded that variation in the sizes of neurons and of their nuclei in the given instance was of a functional character, and polyploidy was untypical for the nervous system of bivalves. Apparently, the polyploidy, as an evolutionary strategy of neuron growth, had no anatomical prerequisites in bivalves, which is similar to CNS oligomerization in higher gastropods, as they are devoid of any functional adaptive sense.     

Body size and invasion success in marine bivalves

The role of body size in marine bivalve invasions has been the subject of debate. Roy et al . found that large-bodied species of marine bivalves were more likely to be successful invaders, consistent with patterns seen during Pleistocene climatic change, but Miller et al . argued that such selectivity was largely driven by the inclusion of mariculture species in the analysis and that size-selectivity was absent outside of mariculture introductions. Here we use data on non-mariculture species from the north-eastern Pacific coast and from a global species pool to test the original hypothesis of Roy et al . that range limits of larger bivalves are more fluid than those of smaller species. First, we test the hypothesis that larger bivalve species are more successful than small species in expanding their geographical ranges following introduction into new regions. Second, we compare body sizes of indigenous and non-indigenous species for 299 of the 303 known intertidal and shelf species within the marine bivalve clade that contains the greater number of non-mariculture invaders, the Mytilidae. The results from both tests provide additional support for the view that body size plays an important role in mediating invasion success in marine bivalves, in contrast to Miller et al . Thus range expansions in Recent bivalves are consistent with patterns seen in Pleistocene faunas despite the many differences in the mechanisms.     

Assessment of the health status of Donax trunculus from the Gulf of Tunis using integrative biomarker indices

For a few years, the littoral of the Gulf of Tunis has been subjected to agricultural activities, industrial, urban and tourist development and consequently submitted to the impact of many chemical and physical stressors. Sub-individual responses (biochemical biomarkers) in bivalves can be used as an early warning system for ecotoxicological risk assessment. However, the influence of many confounding factors such as ecological (e.g. temperature and salinity) or physiological (e.g. reproductive and nutritive status) parameters on biomarker responses must be taken carefully into account. The aim of the present study was to integrate into indices (Integrated Biomarker Response: IBR and Health Status Index: HSI) individual responses of biochemical biomarkers (acetylcholinesterase, catalase, glutathione-S-transferase, thiobarbituric acid reactive substance levels, lactate dehydrogenase and metallothionein-like proteins) and energy reserves (glycogen, lipid levels and total protein concentrations) at sub-individual level, and condition index at individual level in Donax trunculus originating from 4 sites contrasted by their level of contamination in the Gulf of Tunis. Integrated biomarkers indices have been revealed to be efficient and easy tools for environmental managers. Responses of IBR and HSI were compared and their strengths and weaknesses discussed. Results showed that HSI could be an easy tool for risk management whereas IBR results were more informative with regard to the temporal contribution of each biomarker considered in the battery used in the present work. In bivalves from the reference Sidi Jehmi site, the contribution of energy reserves and the condition index reflecting a good general health status clearly influenced the temporal variations of IBR whereas in bivalves from the multi-contaminated Radès Méliane site, temporal variations of IBR were induced mainly by the responses of pollution biomarkers. Previous investigations concerning other level of biological organization (population) are in accordance with the present data (Tlili et al., 2010, Tlili et al., 2011).     

Morphofunctional characterization and ploidy levels of cells in the bivalve digestive gland, with special reference to somatic polyploidy

This study investigates the histological organization and ploidy levels of the digestive gland cells in 29 species of marine, brackish water, and freshwater bivalves belonging to 5 subclasses. In all species studied, the digestive gland epithelium consists of two types of differentiated cells: digestive and basophilic. The nuclei of digestive cells contain the diploid quantity of DNA. Basophilic (secretory) cells often remain diploid also; however, in a number of species all or some of the cells showed an increase in the quantity of DNA per nucleus up to 4c. Tetraploidy of basophilic cells in several species of the subclass Anomalodesmata seems to be due to carnivory. In other species, no apparent correlation was found between selective polyploidy of basophilic cells and environmental conditions or biology traits of the bivalves. Additionally, there was no relationship between the occurrence of polyploid cells and the lifespan of the investigated species. In the bivalve mollusks, somatic polyploidy appears to be an adaptation; it is neither a tissue growth strategy nor a component of the cytodifferentiation program.     

Some aspects of water filtering activity of filter-feeders

On the basis of the previous publications, our new data and the existing scientific literature, we have formulated some fundamental principles that characterize the pivotal roles of the biodiversity of filter-feeders in ecosystems. Among those roles are: (1) the role of ecological repair of water quality, (2) the role of contributing to reliability and stability of the functioning of the ecosystem, (3) the role of contributing to creation of habitat heterogeneity, (4) the role of contributing to acceleration of migration of chemical elements. It is an important feature of the biomachinery of filter-feeders that it removes from water various particles of a very broad range of sizes. Another important principle is that the amount of the organic matter filtered out of water is larger than the amount assimilated so that a significant part of the removed material serves no useful function to the organism of the filter-feeder, but serves a beneficial function to some other species and to the ecosystem as a whole. The new experiments by the author additionally demonstrated a vulnerability of the filtration activity of filter feeders (e.g., bivalves and rotifers) to some xenobiotics (tetradecyltrymethylammonium bromide, heavy metals and some others). The inhibition of the filtration activity of filter-feeders may lead to the situation previously described as that of an ecological bomb of the second type.     

中国淡水双壳类特有种的地理分布

通过查阅有关文献整理得出,中国淡水双壳类特有种计有58种,隶属于双壳纲(Bivalvia)2科17属,其中主要是蚌科(Unionidae)的种类(16属57种)。我国淡水双壳类特有种的组成和区系成分,以东洋界华中区的种类占绝对优势,仅有少数种类渗透到古北界;特有种在我国16个省有分布,但主要集中分布于江西、湖南、安徽、浙江、江苏五省。双壳类特有种的形成和保存可能与我国古地理环境及其生活的水域环境有关。     

Parasite-mediated shell alterations in Recent and Holocene sub-Antarctic bivalves: the parasite as modeler of host reaction

Abstract. New data on shell reactions elicited by larval digeneans in bivalves from Recent sub-Antarctic populations and late Holocene Patagonian deposits are reported. Shell alterations, which are traces of digenean trematode infections, were found affecting intertidal bivalve populations from Malvinas (Falkland) Islands, Burdwood Bank, Beagle Channel, and from Holocene deposits at Tierra del Fuego (Argentina). The bivalve species involved belonged to the families Nuculanidae, Cyamiidae, and Neoleptonidae. Such reactions consisted of quite unusual dome or igloo-shaped calcifications on the inner shell surface; the similarities and uniqueness of this reaction in different bivalve species reported here suggest that the invasive agent is the same. Based on previous findings of morphologically identical shell alterations in Gaimardia trapesina (Bivalvia, Gaimardiidae) from Magellanic and sub-Antarctic waters, it is suggested that the parasites responsible for the traces reported here belong to a digenean platyhelminth species of the Gymnophallidae genus Bartolius . The host bivalves reported here belong to three different superfamilies, and share a similar crystalline shell microstructure: aragonite with homogeneous structure. After a review of the available information dealing with bivalve shell-mantle reactions against digeneans, it is hypothesized that parasites are responsible for the modeling of the host response they elicit. However, although the specific characteristics of the reaction depend on the parasite, they would probably be constrained by some characteristics of the host shell structure.     

Impact of Polluted Bottom Deposits on the Species Structure and Abundance of Bivalves in Peter the Great Bay,Sea of Japan

Data from long-term (1979–1988) studies of bivalve fauna and of the content of priority pollutants in the bottom deposits of Peter the Great Bay have been analyzed. It was established that the biomass, population density, number of species, and the species diversity indexes of Shannon-Weiner and of the Pielou evenness of bivalves negatively correlated with the total pollution factor, TPF, of bottom sediments. Changes in the ecological parameters of bivalves with an increase in pollution occurred in spurts within the 3.4–3.6 interval of TPF values. The area of such values covered not only the coastal zone of Vladivostok, but also a considerable part of Amursky Bay.     

Climate change, species range limits and body size in marine bivalves

We use data on the Pleistocene and modern range limits of Californian marine bivalves to show that species that shifted their geographical ranges in response to Pleistocene climatic fluctuations were preferentially drawn from the large end of the regional body size–frequency distributions. This difference is not due to phylogenetic effects (i.e. dominance of extralimital species by a few large-bodied clades), differences among major ecological categories (burrowing versus surface-dwelling, or suspension feeding versus non-suspension feeding), or differences in modes of reproduction and larval development. In addition, we show that successful invasive species of bivalves in present-day marine habitats also tend to be large-bodied, despite the difference in mechanisms between present-day and Pleistocene range expansions. These results indicate that range limits of large-bodied bivalve species are more unstable than small-bodied ones, and that body size and its correlates need to be considered when attempting to predict the responses of marine communities to climate change, biotic interchanges and human-mediated invasions.     

Dynamics of taxonomic diversity of bivalves in the Phanerozoic

Changes in the taxonomic composition of bivalves during the Phanerozoic are considered. Each period is characterized by a special set of taxa, in particular, families. Changes in taxonomic diversity, the episodes of maximum and minimum diversity are established and compared with those of other invertebrate groups. In general, the taxonomic diversity of bivalves gradually increased, except for a sharp decrease in the Early Triassic.     

青藏高原白垩纪双壳类生物地理

青藏高原白垩纪沉积见于６条东西向延伸的条带内。双壳类主要发育于这些条带的Ｂｅｒｒｉａｓｉａｎ,Ａｐｔｉａｎ－Ａｌｂｉａｎ,Ｃｅｎｏｍａｎｉａｎ－Ｔｕｒｏｎｉａｎ,Ｃｏｎｉａｃｉａｎ－Ｓａｎｔｏｎｉａｎ和Ｃａｍｐａｎｉａｎ－Ｍａａｓｔｒｉｃｈｔｉａｎ５个时期的地层。雅鲁藏布江缝合线为白垩纪双壳类地理分布的主要控制界线。早白垩世期间,雅鲁藏布江缝合带以南的喜马拉雅地区的双壳类Ｐｅｔｒｏｃｅｒａｍｕｓ,     

Native Parasites Adopt Introduced Bivalves of the North Sea

Introduced species may have a competitive advantage over native species due to a lack of predators or pathogens. In the North Sea region, it has been assumed that no metazoan parasites are to be found in marine introduced species. In an attempt to test this assumption, we found native parasites in the introduced bivalves Crassostrea gigas and Ensis americanus with a prevalence of 35% and 80%, respectively, dominated by the trematode Renicola roscovita. When comparing these introduced species with native bivalves from the same localities, Mytilus edulis and Cerastoderma edule, trematode intensity was always lower in the introduced species. These findings have three major implications: (1) introduced bivalves are not free of detrimental parasites which raises the question whether introduced species have an advantage over native species after invasion, (2) introduced bivalves may divert parasite burdens providing a relief for native species and (3) they may affect parasite populations by influencing the fate of infectious stages, ending either in dead end hosts, not being consumed by potential final hosts or by adding new hosts. Future studies should consider these implications to arrive at a better understanding of the interplay between native parasites and introduced hosts.     

Death assemblages of molluscs on St Martin's Flats, Isles of Scilly: a surrogate for regional biodiversity?

We test the hypothesis that the biodiversity of the death assemblage of shelled molluscs (gastropods and bivalves) on a single sandflat is representative of the biodiversity of the regional living fauna from the complete spectrum of habitat types, and can therefore be used as a surrogate for the purposes of rapid biodiversity assessment. Two biodiversity indices considered appropriate for such an assessment are average taxonomic distinctness (⁺) and the variation in taxonomic distinctness (⁺), which are, respectively, measures of the degree to which the species are taxonomically related to each other (i.e. the average taxonomic spread), and the degree to which taxa are over or under represented (i.e. the evenness of the distribution across the taxonomic tree). In each case, measured values were compared with the regional living species pool using a randomisation test. Collections and identifications of shells were made by both a non-expert in mollusc taxonomy and by taxonomic experts, the latter using microscopic examination of sediment samples as well as simple surface searches for macro-species. In all studies, ⁺ for the gastropods in the death assemblage was fully representative of the regional living fauna, but for bivalves it was significantly lower. This is because most of the bivalves were characteristic of the sandflat habitat, which introduced a bias, whereas post-mortem transport of gastropods, characterising exotic habitats, is more random. For gastropods, in all studies but one, ⁺ was significantly higher than expected from a random sample of the regional species pool, and for bivalves this was the case for all studies, suggesting the over-representation of some taxa and the under-representation of others. For the total shelled molluscan fauna (gastropods + bivalves) all ⁺ values were below, and all ⁺ values above, expectation. Results obtained by experts and a non-expert in mollusc taxonomy did not differ. In general, death assemblages at a single location are only likely to be representative of a wider region if there is randomisation as a result of post-mortem transport processes.     

Biogeography of the Late Triassic wallowaconchid megalodontoid bivalves

Discoveries of Late Triassic alatoform bivalves (family Wallowaconchidae) in Alaska and in south Asia and Arabia reveal a broad distribution for these tropical bivalves, overturning the concept of these bivalves being endemics of offshore island arc terranes in eastern Panthalassa. They occupied an area extending from central Tethys to the eastern Pacific margin of Panthalassa. The Tethyan wallowaconchids occur in nearshore environments on the north margin of Gondwana, indicating an environmental tolerance for continental shelf settings in addition to their primary occurrence on isolated oceanic islands. The new sites reveal a taxonomic diversity among wallowaconchids. Wallowaconchids present in India are conspecific with Wallowaconcha raylenea, the type species of Wallowaconcha, whereas wallowaconchids in Arabia are an undescribed taxon and wallowaconchids in south-central Alaska are small in size and a different undescribed taxon. All known wallowaconchids are of Norian age and they appear to be a wide-ranging component of Late Triassic tropical biotas.     

Opisoma excavatum Boehm,a Lower Jurassic photosymbiotic alatoform‐chambered bivalve

Alatoform bivalves are a polyphyletic group characterized by antero‐posteriorly compressed shells and a ventro‐lateral wing originating from a tight fold of the shell wall. This bizarre shell morphology is interpreted as an adaptation for algal photosymbiosis in heliophilous bivalves. The group contains the living heart cockle Corculum together with four extinct genera ranging in age from the Permian to the Jurassic. The Jurassic alatoform bivalve is Opisoma, which has an aragonitic shell that is divided into two regions, both with different functions: one for stabilization, the other for hosting symbionts. The dorsal part of the shell is massive and played the stabilization role. The ventral part has a very thin and fragile shell that permitted the transmission of light into the internal tissues harbouring photosymbionts. The morphology of this delicate ventral part has thus far remained obscure, due to lack of preservation. Accumulations of Opisoma excavatum Boehm with exquisitely preserved shells containing the fragile winged ventral parts are common within the Pliensbachian shallow‐water, lagoonal carbonate succession of the Rotzo Formation of northern Italy. The wings have internal curved chambers limited by septa parallel to the wing edge. The shell of the ventral part consists of irregular fibrous prismatic and homogeneous structures which progressively infill the chambers. As the chambered wings are analogous structures among alatoform bivalves, they are no longer considered a taxonomic character. According to the observed shell orientation in the field and the consequent organization of the soft parts, Opisoma had an opisthogyrate shell.     

西藏南部白垩纪岗巴群的双壳类及其生物地理意义

描述双壳类化石４２种,建立１０新种：Ｇｒａｍｍａｔｏｄｏｎ（Ｎａｎｏｎａｖｉｓ）ｍｉｎｕｍ ｓｐ．ｎｏｖ．,Ｐｒｏｐｅａｍｕｓｓｉｕｍ（Ｐ．）ｔｉｂｅｔｅｎｓｐ ｅｐ．ｎｏｖ．,Ｐｌｉｃａｔｕｌａ ｈｉｍａｌａｙｅｎｓｉｓ ｓｐ．ｎｏｖ．,Ｐｓｅｕｄｏｌｉｍｅａ ｄｕｏｄｅｃｉｃｏｓｔａｔａ ｓｐ．ｎｏｖ．,Ｐｙｃｎｏｄｏｎｔｅ（Ｐｈｙｇｒａｅａ）ｇａｍｂａｅｎｓｉｓ ｓｐ．ｎｏｖ．,Ｎｏｔｏｔｒ     

Filtration rate capacities in 6 species of European freshwater bivalves

Summary Filtration rate capacities in undisturbed freshwater bivalves were determined by means of two different methods (indirect clearance and suction methods) in Anodonta anatina (L.), Unio tumidus Philipsson, Unio pictorum (L.), Unio crassus Philipsson, Dreissena polymorpha (Pallas) and Sphaerium corneum (L.). In A. anatina, D. polymorpha, and S. corneum the filtration rate (FR, 1 h^-1) at 19–20°C as a function of dry tissue weight (DW, g) or ash-free dry weight (AFDW, g) could be expressed by the equations: 1.10 DW^0.78, 6.82 DW^0.88, and 2.14 AFDW^0.92, respectively. In U. tumidus, U. pictorum, and U. crassus filtration rates were comparable with those of A. anatina. In D. polymorpha the b value of the corresponding regression of gill area on dry weight was 0.87. The rates of water transport in freshwater bivalves are 2–8 times lower than in marine bivalves of comparable size. A corresponding difference in the filtration rate per gill area unit is found. The measured filtration rates in undisturbed bivalves are substantially higher (at least 4 times) than previously reported. This indicates that the impact of bivalve water processing on freshwater ecosystems is greater than hitherto suggested.     

Strontium isotope stratigraphy of Cretaceous hippuritid rudist bivalves: rates of morphological change and heterochronic evolution

Strontium isotope stratigraphy of 17 localities of rudist formations in the region of the former Mediterranean Tethys has provided a reliable and precise stratigraphical frame for the evaluation of morphological change in hippuritid rudist bivalves during the Coniacian–Campanian. The phyletic lineage Vaccinites cornuvaccinum (Bronn)–Vaccinites chaperi (Douvillé) evolved from the Early Coniacian until the Early Campanian and is characterized by phyletic size increase and allometric growth, as shown by morphometrical measurements of 102 shells. These chronospecies intergrade in the Late Coniacian so that V. cornuvaccinum is considered to be a reliable marker species for the Coniacian. The taxonomy of Vaccinites alpinus (Douvillé) is discussed and the species is recognized as a senior synonym of Vaccinites ultimus (Milovanovi ). It appears first in the Late Santonian and the last appearance is probably in Late Campanian. Both lineages are characterized by phyletic size increase and peramorphic evolution involving hypermorphosis. A doubling of the length of the mantle margin occurred within 5 m.y. in both lineages. The results demonstrate that the combination of morphometric analyses and stratigraphical precision provides an important tool for the delineation of tempo and mode of evolution in rudist bivalves. Strontium isotope stratigraphy resulted in a considerable revision of the ranges of the species investigated. As the stratigraphy of many Tethyan carbonate platforms relies on the distribution of rudist bivalves, and the species investigated are abundant in many rudist formations, the history of many Late Cretaceous carbonate platforms must be re-evaluated.     

Alzheimer 病生物标志物表达的研究进展

目前,对阿尔茨海默病（AD）的诊断和治疗还存在一定的局限性和困难,临床上筛选出敏感性和特异性高的生物标志物有助于对AD的诊断和鉴别诊断,本文就与淀粉样变过程、胆固醇代谢过程及氧化应激过程的标志物的研究现状及其对临床的价值作一综述。