Effects of copper on the fitness of the Chilean scallop Argopecten purpuratus (Mollusca: Bivalvia)

Exposure to high concentrations of metals can affect populations and individuals at morphological, physiological, biochemical or genetic levels. Metal pollution is a source of environmental stress that can have deleterious effects on organisms and generate selective pressure upon populations. This work attempts to establish whether concentrations of copper, above physiological requirements, can affect the genetic structure of a cohort of Chilean scallop Argopecten purpuratus. Following the determination of LC₅₀ for 96 h experiments, other acute toxicity tests were carried out, exposing the juveniles to solutions of 150 ppb copper for 120 h. Dead, surviving and control individuals from these bioassays were genetically characterized for five polymorphic loci, Isocitrate dehydrogenase (Idh), Octopine dehydrogenase (Ocdh), Phosphogluconate dehydrogenase (Pgd), Leucine aminopeptidase (Lap) and Phosphoglucose isomerase (Pgi). Results showed no significant differences in allele and genotypic frequencies between surviving and dead individuals, although for the same groups significant differences were found in estimated mean heterozygosity. Pgi and Ocdh showed significantly different heterozygosity values for dead and surviving individuals. A positive relationship between multilocus heterozygosity and survival was found for young A. purpuratus exposed to high copper concentrations; thus, we found evidence of a differential response to exposure to high copper concentrations, related to degree of heterozygosity.     

The karyotype of Nodipecten nodosus (Bivalvia: Pectinidae)

Earlier karyotypical work on Nodipecten nodosus embryos indicated that this species has a diploid number of 38, with six pairs respectively of metacentric and submetacentric chromosomes and seven pairs of subtelocentric chromosomes, although there were some difficulties in obtaining complete metaphases. The present work provides additional results on specific regions of the chromosomes in N. nodosus and, by meiotic studies, confirms the chromosome number with more reliability. Active nucleolar organizer regions (NOR), detected in mitotic metaphases from embryos, can be characterized in N. nodosus by a high level of heteromorphism of NOR-sites, indicating that these regions are not appropriate as chromosomal markers in this species. The procedure for detecting constitutive heterochromatin of chromosomes allowed us to observe most of the heterochromatic blocks at a pericentromeric position and some at telomeric and interstitial positions. The analysis of meiotic chromosomes from gonad tissue revealed the presence of 19 bivalents during metaphase I, all homomorphic and isopicnotic, confirming the previously described diploid chromosomal number of 38 for N. nodosus. From these results, some evolutionary aspects of the Pectinidae are briefly discussed.     

Phylogeny and spatio-temporal distribution of European Pectinidae (Mollusca: Bivalvia)

Phylogenetic relationships within Pectinidae (Bivalvia, Pteriomorphia) have been investigated primarily for Pacific and Western Atlantic or commercially valuable taxa. Most molecular phylogenetic studies have revealed monophyly of pectinid bivalves but interrelationships of the different clades are still inconsistent. However, non-commercial European Pectinidae has mostly been neglected in earlier investigations and therefore the evolution and radiation of the European Pectinidae is poorly understood. Since the fossil record of this group is well investigated, the evolutionary age of phylogenetic diversification and radiation events within this group can be dated. Thus, the connection of geological and climatic changes to radiation events within this group can be assessed. We investigated the phylogenetic relationships within European Pectinidae using mitochondrial (12S and 16S) and nuclear (18S, 28S and H3) gene markers and performed relaxed molecular clock approaches to gain information on the evolutionary age and the connection between Cenozoic climatic changes and diversification within this group. The results show concordance of radiation events with the Middle Miocene cooling event and the following climatic period with slowly decreasing temperatures. However, geological changes such as the uplift of the Gomphotherium Landbridge or the closure and re-opening of the Strait of Gibraltar also had great impact on diversification and distribution patterns within European Pectinidae.     

Sequence analysis of the ribosomal DNA internal transcribed spacer region in some scallop species (Mollusca: Bivalvia: Pectinidae).

The internal transcribed spacer (ITS) region of the ribosomal DNA from the European scallops Aequipecten opercularis, Mimachlamys varia, Hinnites distortus, and Pecten maximus was PCR amplified and sequenced. For each species, three or five clones were examined. The size ranged between 636 and 713 bp (ITS1, 209-276 bp; 5.8S rRNA gene, 157 bp; ITS2, 270-294 bp) and GC content ranged between 47 and 50% (ITS1, 43-49%; 5.8S rRNA gene, 56-57%; ITS2, 44-49%). Variation within repeats was minimal; only clones from M. varia and P. maximus displayed a few variable sites in ITS2. Among scallops, including Chlamys farreri whose ITS sequence appears in databases, significant variation was observed in both ITS1 and ITS2. Phylogenetic analysis using ITS1, ITS2, or both spacer sequences always yielded trees with similar topology. Aequipecten opercularis and P. maximus grouped in one clade and the other three scallops (C. farreri, M. varia, and H. distortus) in another, where M. varia and H. distortus are the more closely related species. These results provide new insights into the evolutionary relationships of scallop species and corroborate the close evolutionary relationship between the tribes Aequipectinini and Pectinini previously deduced from 18S rDNA sequences.     

Distribution of catecholamines,indoleamines, and their precursors and metabolites in the scallop,Placopecten magellanicus (Bivalvia,Pectinidae)

Summary 1. Although monoamines are well-known to play important roles in molluscan physiology, we are far from fully understanding the synthetic and degradative pathways of these substances, particularly in commercially important bivalve species. In the present study endogenous catecholamines, indoleamines, and their possible precursors and metabolites were detected in the scallop,Placopecten magellanicus, by high-performance liquid chromatography coupled to electrochemical detection.2. Chromatographic analysis of CNS (cerebral, pedal, and parietovisceral combined), gill, gonad, kidney, mantle, liver, heart, fast adductor muscle, and foot disclosed the presence of the catecholamines 3,4-dihydroxyphenylalanine, dopamine, norepinephrine, and epinephrine and their metabolites normetanephrine, metanephrine, 3,4-dihydroxyphenylacetic acid, and homovanillic acid.3. Dopamine was detected most frequently and most consistently among all catecholamines. The concentrations of dopamine (1400 pg/mg wet weight) and its major metabolite 3,4-dihydroxyphenylacetic acid (300 pg/mg wet weight) were highest in the CNS. Following the CNS, dopamine was also abundant in other tissues such as heart, foot, and gill. The concentration of norepinephrine (1000 pg/mg wet weight) was highest in the CNS followed by the heart (700 pg/mg wet weight) and gill (600 pg/mg wet weight).4. The indoleamine, 5-hydroxytryptamine, was present in considerable amounts in all tissues, but its content was highest in the foot (2700 pg/mg wet weight) followed by the CNS (1150 pg/mg wet weight) and gonad (1000 pg/mg wet weight). The precursor 5-hydroxytryptophan was also abundant in the foot followed by the gonad, CNS, and heart.5. The oxidative metabolite 5-hydroxy-3-indole acetic acid was detected in the largest amount in CNS (200 pg/mg wet weight), whereasN-acetyl-5-hydroxytryptamine was detected in trace amounts in CNS, gonad and foot. This study also presents evidence for -glutamyl dopamine and -glutamyl 5-hydroxytryptamine as the possible alternate catabolic products of dopamine and 5-hydroxytryptamine, respectively, as previously described in gastropods.6. Thus, the detection of monoamines and their precursors and metabolites in scallop strongly suggests the presence of mammalian-type enzymic action of hydroxylation, oxidation, and methylation pathways leading to synthesis and degradation of detected compounds. Furthermore, this is the first study to disclose the evidence of nonconventional metabolic pathways for dopamine (-glutamyl dopamine dopamine dihydroxyphenylacetic acid homovanillic acid) and 5-hydroxytryptamine (-glutamyl 5-hydroxytryptamine 5-hydroxytryptamine 5-hydroxy-3-indoleacetic acid) inactivation in a bivalve species.     

The distribution, size and age compositions, and growth of the scallop Mizuhopecten yessoensis (Bivalvia: Pectinidae) in the northwestern Tatar Strait

The distribution patterns, size, age structure, and growth of the scallop Mizuhopecten yessoensis were studied in the northwest of the Tatar Strait, Sea of Japan. We determined that the northern boundary of the species range occurred in the region of Tabo Bay, at 51°37?? N. The distribution of the mollusk, depending on latitude, depth, substrate, and age, was determined. The maximum depth of M. yessoensis habitat is 138 meters, the maximum shell height is 200 mm, and the maximum age is 14 years. The differences in the growth rate of the Japanese scallop in different areas are discussed in relation to the conditions of its habitat in the northern part of its range.     

The Mitochondrial Genomes of Two Scallops, Argopecten irradians and Chlamys farreri (Mollusca: Bivalvia): The Most Highly Rearranged Gene Order in the Family Pectinidae

Molluscs in general and bivalves in particular, exhibit an extraordinary degree of mitochondrial gene order variation when compared with other metazoans. Here, we determined the mitochondrial genomes of two scallops Argopecten irradians and Chlamys farreri. The complete mitochondrial genome of A. irradians is 16,211 nts in length and the nearly complete mitochondrial genome of C. farreri is 20,789 nts in length. Both of the genomes contain 35 genes including 12 protein-coding genes, 2 ribosomal RNAs, and 21 transfer RNAs. In contrast to the typical animal mitochondrial genome, both of them lack one protein-coding gene atp8 and two trnSs, but show an additional copy of trnF in A. irradians and of trnM in C. farreri, respectively. Gene order and genome content were compared among the four sequenced scallops. Gene arrangement of C. farreri closely resembles that of Mizuhopecten yessoensis. However, two genomes of C. farreri and A. irradians show only three small identical gene blocks and two genomes of A. irradians and Placopecten magellanicus share only one gene block. Comparison of the gene arrangement demonstrated that the four scallops share few identical gene blocks although they belong to the same family. This feature is seldom observed in Metazoa, even in other molluscan classes. The dramatic gene rearrangement often occurs in bivalves, especially in marine bivalves. In addition, comparisons of genomic character among bivalves are also presented.     

Larval development of the shell and the shell gland inMytilus (Bivalvia)

Summary In the newly hatched larva ofMytilus galloprovincialis the larval shell field almost totally invaginates to form a shell gland. Only very few cells remain outside and they meet at one point. Only these cells secrete the pellicle, which in the beginning is protected by the glycocalyx and the microvilli of the surrounding cells. The invaginated cells do not participate in pellicle secretion. The secretion partly passes through infoldings of the apical cell membrane. Mineralization of each valve begins along the hinge line, continues to the valve margins and includes the valve centre.     

A Model for the Stochastic Multidimensional Growth of Mizuhopecten yessoensis (Jay, 1857) (Bivalvia: Pectinidae)

Russian Journal of Marine Biology - A mathematical model that describes the growth of a complex of characters in an organism that inhabits a stochastic environment is discussed. The concepts of...     

Geographical variation in shell shape of the pod razor shell Ensis siliqua (Bivalvia: Pharidae)

The present study assessed the existence of variation in the shell shape of the pod razor shell (Ensis siliqua) throughout its distributional range in the north-eastern Atlantic. Shells of E. siliqua caught at seven collecting sites (three in Portugal, three in Spain and one in Ireland) were studied by geometric morphometric methods, using both landmark- and contour-based methods. Both approaches (landmarks inside the valves and shell outline) discriminated the shells from Aveiro (centre of Portugal) and Strangford Lough (Ireland) from those caught in the nearby localities (remaining Portuguese and Spanish sites, maximum distance of 550 km by sea). Landmark analysis revealed that shells from Aveiro were more similar to shells from Ireland (~1,500 km far away). Contour analysis revealed that shells from Aveiro had a shape with a comparatively larger height-to-width ratio, whereas shells from Ireland showed a slightly more curved outline than in the remaining sites. Landmark- and contour-based methods provided coherent complementary information, confirming the usefulness of geometric morphometric analyses for discerning differences in shell shape among populations of E. siliqua. A brief review of previous applications of geometric morphometric methods to modern bivalve species is also provided.     

Molecular Data from the 16S rRNA Gene for the Phylogeny of Pectinidae (Mollusca: Bivalvia)

The phylogenetic relationships among the species belonging to the family Pectinidae are still an issue of debate. The mitochondrial DNA sequences from the large ribosomal RNA gene may be of great value for systematic and phylogenetic studies within families. Partial sequences of the 16S rRNA gene were obtained for the scallop species Adamussium colbecki, Aequipecten opercularis, Chlamys glabra, C. islandica, C. varia, and Pecten jacobeus and compared with the published sequence of Pecten maximus. The present molecular data show that Chlamys are polyphyletic and do not support the assignment of these species to the two subfamilies Chlamydinae and Pectininae. Moreover, the minimal genetic distance between P. maximus and P. jacobeus suggests that they could belong to the same species. Received: 24 May 1999 / Accepted: 1 September 1999     

Estimating the biomass of freshwater mussels (Bivalvia: Unionidae) from shell dimensions

Packs of autumn-shed maple leaves were placed at coal ash effluent-exposed and reference sites in streams on December 5, 1977 and removed after 27 and 96 days. Leaf surface area (cm²/leaf) and disc weight (ash-free dry wt/15 mm disc) were greater at the effluent-exposed site than at the reference site after 96 days (p < .001). ATP content of leaves from the reference stream quadrupled between 27 and 96 days while ATP content of effluent-exposed leaves remained low. Macroinvertebrates colonized the leaf packs in the reference site but were not found on or in effluent-exposed packs. We concluded that leaf processing beyond the leaching of soluble organics did not occur in the effluent-exposed packs owing to reduced colonization and decomposition by fungi. Since stream invertebrates prefer decomposed leaf material and animals grow faster on leaves colonized by microbes, the ash effuent appears to indirectly affect macroinvertebrates by interfering with leaf decomposition and thus reducing the quality of their food.     

Primary cell culture from embryos of the Japanese scallop Mizuchopecten yessoensis (Bivalvia)

Primary cell cultures obtained from embryos of Mizuchopecten yessoensis (Bivalvia) survived for four months. Although the number of cells progressively decreased during the cultivation, mitotic cells were observed both at the first stages and at the end. A possibility of growing marine invertebrates cells in long term primary culture is discussed.     

Molecular phylogeny of the family Pectinidae (Mollusca: Bivalvia) based on mitochondrial 16S and 12S rRNA genes

Pectinidae is a large bivalve family characterised by almost circular, flat shells. Species are distributed worldwide and fall into three life-styles: swimming, byssally attached to hard substrates, and cemented to rocks with one valve. Despite these very different life strategies, pectinid shells are highly conservative in shape and offer few clues for the unravelling of phylogenetic issues. Consequently, phylogenetic studies based on morphological features have not yielded conclusive results. We thus set out to analyse partial sequences of mitochondrial 12S and 16S rRNA genes from 23 species of 16 genera with molecular techniques. The results are largely in contrast, both at the genus and the subfamily level, with the systematic classifications based on adult morphological characters, whereas they agree with the morphological classifications based on the more conserved non-adaptive features.     

Geometrical and crystallographic constraints determine the self-organization of shell microstructures in Unionidae (Bivalvia: Mollusca)

Unionid shells are characterized by an outer aragonitic prismatic layer and an inner nacreous layer. The prisms of the outer shell layer are composed of single-crystal fibres radiating from spheruliths. During prism development, fibres progressively recline to the growth front. There is competition between prisms, leading to the selection of bigger, evenly sized prisms. A new model explains this competition process between prisms, using fibres as elementary units of competition. Scanning electron microscopy and X-ray texture analysis show that, during prism growth, fibres become progressively orientated with their three crystallographic axes aligned, which results from geometric constraints and space limitations. Interestingly transition to the nacreous layer does not occur until a high degree of orientation of fibres is attained. There is no selection of crystal orientation in the nacreous layer and, as a result, the preferential orientation of crystals deteriorates. Deterioration of crystal orientation is most probably due to accumulation of errors as the epitaxial growth is suppressed by thick or continuous organic coats on some nacre crystals. In conclusion, the microstructural arrangement of the unionid shell is, to a large extent, self-organized with the main constraints being crystallographic and geometrical laws.     

Chromosome rearrangements in Pectinidae (Bivalvia: Pteriomorphia) implied based on chromosomal localization of histone H3 gene in four scallops

Chromosomal structural rearrangement in four scallops, Chlamys farreri (n = 19), Patinopecten yessoensis (n = 19), Chlamys nobilis (n = 16) and Argopecten irradians (n = 16), was studied by fluorescence in situ hybridization using histone H3 gene probes. The results show that histone H3 gene sites differ strikingly with regard to number, location, and intensity among, or even within these species. For example, two histone H3 gene loci were detected on the metaphase chromosomes of P. yessoensis, while one locus was found in the others. In P. yessoensis, differing intensities of hybridization signals were detected between homologues 5 and 11, and within homologue 11. These data suggest that the histone H3 gene is a qualified chromosome marker for the preliminary understanding of the historical chromosomal reconstructing of the Pectinidae family. The variable distribution patterns of the histone H3 gene suggest that gene duplication/diminution as well as chromosome rearrangements by inversion and translocation may have played important roles in the genomic evolution of Pectinidae. We also compiled our present results with former published data regarding the chromosome mapping of rDNAs in species of the Pectinidae family. Such comparative chromosomal mapping should improve our understanding of historical chromosomal reconstructions of modern-day scallops.     

Molecular phylogenetics of the Pectinidae (Mollusca: Bivalvia) and effect of increased taxon sampling and outgroup selection on tree topology

Evolutionary relationships of the Pectinidae were examined using two mitochondrial genes (12S rRNA, 16S rRNA) and one nuclear gene (Histone H3) for 46 species. Outgroup taxa from Propeamussidae, Spondylidae and Limidae were also sequenced to examine the impact of outgroup choice on pectinid topologies. Our phylogenetic analyses resolved the Pectinidae as monophyletic, but many of the subfamilies and tribes within the family do not form monophyletic clades. The paraphyletic Aequipectinini group is the most basal member of the Pectinidae, with the Chlamydinae and Palliolinae representing the most recently derived pectinid groups. These results are in contrast with the current morphological hypothesis of Pectinidae evolution, which suggests the Chlamydinae and Pallioline are basal groups within the Pectinidae. Ingroup topology was found to be sensitive to outgroup choice and increasing taxon sampling within the Pectinidae resulted in more robust phylogenies.