Bathymetric patterns of genetic variation in a deep-sea protobranch bivalve, Deminucula atacellana

The origin of the deep-sea benthic fauna is poorly understood and represents an enormous gap in our understanding of basic evolutionary phenomena. One obstacle to studying evolutionary patterns in the deep sea has been the technical difficulty of measuring genetic variation in species that are typically minute, rare, and must be recovered from extreme depths. We used molecular genetic techniques to quantify variation in the 16S rRNA mitochondrial gene within and among populations of the common protobranch bivalve Deminucula atacellana (Schenck, 1939). We analyzed 89 individuals from nine samples collected in the 1960s along a depth gradient from 1100 to 3800 m in the western North Atlantic. Genetic variability within populations is much lower than between populations, and peak haplotype numbers occur near the center of its depth distribution. Continental slope (<2500 m) and rise (>2500 m) populations were genetically distinct despite the lack of any obvious topographic or oceanographic features that would impede gene flow. These findings indicate that the deep-sea macrofauna can have strong population structure over small (134 km) spatial scales, similar to that observed in shallow-water and terrestrial organisms. This surprisingly high biodiversity at the genetic level affords the potential for adaptation and evolutionary diversification, the ultimate historical causes of high species diversity in the deep-sea benthos. Received: 24 July 1997 / Accepted: 26 January 1998     

Larval dispersal of a deep-sea hydrothermal vent bivalve from the Galápagos Rift

The prodissoconch morphology of an unclassified mytilid from a hydrothermal vent on the Galápagos Rift indicates the presence of a planktotrophic larval stage with longrange dispersal capabilities. Recorded abyssal currents are probably sufficient to transport such larvae hundreds of kilometers. It is suggested that one or more aspects of the unusual biological or physico-chemical conditions (such as high microbial densities, elevated water temperatures, and hydrogen sulfide concentrations) encountered at vents, provide a stimulus to larval settlement. Such a behavioral response, perhaps coupled with a gregarious settling response, would provide a means of concentrating relatively sedentary organisms in and around these restricted, geographically isolated regions.     

Assemblage shift following population collapse of a non-indigenous bivalve in an urban lagoon

The quahog Mercenaria mercenaria has been introduced repeatedly to the Pacific coast of North America, but only one population is known to have become established. In the 1970s, the population of M. mercenaria at Colorado Lagoon, in Los Angeles County, California (33^o46′16″N, 118^o08′05″W), was estimated at more than 300,000 individuals. To determine the current status of this non-indigenous species (NIS), in 2009, we sampled 57 intertidal and 20 shallow subtidal plots, identifying and quantifying collected bivalves. No quahogs were found among the 2,490 living bivalves in our plots, though two were found intertidally outside of our plots. The M. mercenaria population has thus collapsed since 1980, but the native community has not recovered. Six of the fourteen living bivalve species we encountered were NIS; three are new records for the location, including the clam Venerupis philippinarum, which made up 87.6% of collected individuals. Though M. mercenaria is likely on its way to extinction on the US Pacific coast, the bivalve assemblage at this location remains heavily dominated by NIS.     

Sclerotized protein in the shell matrix of a bivalve mollusc

The epsilon-amino groups of lysine and phenolic groups of tyrosine are most heavily concentrated in the newlydeposited organic matrix of the shell of the bivalve Mercenaria mercenaria. A phenoloxidase enzyme which oxidizes L-dihydroxyphenylalanine is present only in this new area of the shell matrix. Scanning electron micrographs of calcified secretions of the shell show that accretion lines, thought to be layers of organic matrix separating diurnal acceretions of calcium carbonate, are not developed until up to 4 d after deposition of shell material. These results suggest that the shell matrix is hardened by some kind of polymerization, and that lysine and tyrosine residues in the matrix are involved in the process. Accretion lines in polished and etched sections become visible only after complete hardening of the polymer occurs.     

Responses of Asterias rubens to bivalve prey in a Y-maze

Experiments carried out in a Y-maze apparatus using a constant number of mussels, Mytilus edulis L., as prey showed the presence of a food-seeking period in the predatory starfish Asterias rubens L. collected in the Menai Strait, Anglesey, North Wales. The starfish orientated towards the mussels in the experiment conducted from Novemeber-December to May. The food-seeking activity was not significantly different from random expectation between June and October. It is suggested that this seasonal change in the behaviour of A. rubens can be due either to a lowering of chemo-sensitivity and failure to respond by A. rubens, or to a seasonal change in production of attractant(s) by the prey, or to a combination of the above. A. rubens does not move towards a bait of oyster spat (Ostrea edulis L.) in the Y-maze unless it has been previously conditioned to eat the oysters for about a month. In the Menai Strait, oysters would rarely be encountered by A. rubens and, therefore, the experiments confirmed the concept of ingestive conditioning (Wood, 1968).     

Digestion in a subtidal population of Mercenaria mercenaria (Bivalvia)

The digestive processes of Mercenaria mercenaria (Linn.) were studied in a natural subtidal population. Hourly sampling of 4 to 5 quahogs was conducted over one 25 h period in August, 1978, at Woods Hole, Ma., USA. Crystalline style length did not vary significantly with time, tide, particulate C, N or suspended material in the water. Changes in secretory activity of the style sac epithelium were not evident from histological sections. Based on cellular morphological differences, digestive tubules were individually classified into one of 4 categories, indicative of the state of intracellular digestion within the digestive cells. All 4 tubule types were present in individuals from each sample hour, signifying that intracellular digestion occurs continually within the digestive gland. A 3 h time lag is evident between times of peak C, N or suspended materials and apparent peak levels of absorptive (Type II) tubules.Contribution No. 76 Marine Science Institute, Northeastern University; Nahant, MA 01908, USA     

Inheritance of a nuclear DNA polymorphism assayed in single bivalve larvae

We examined the inheritance of theMytilus edulis CaM-1 Intron 3 locus, a non-coding DNA locus with two potentially neutral length-variants. The polymerase chain reaction (PCR) was used to determine theCaM-1 genotype for 799 larvae obtained from 11 laboratory crosses. Larvae were typed singly only 8 to 24 h after fertilization. We find evidence that each allele can be inherited from either sex, that there are no barriers to fertilization between gametes of different genotypes, and that most larvae have genotypes compatible with Mendelian inheritance of the locus. Deviations from expected genotype frequencies were found in some crosses; we suggest that a contributing factor is aneuploidy in early larvae, but a major cause is more likely to be selection at a locus linked toCaM-1, occurring under the artificial laboratory culture conditions. This study demonstrates the feasibility of applying molecular genetic techniques to early larval stages of marine bivalves, and presents a new non-destructive biopsy method for DNA analysis from living adult mussels.     

Depth-related shift in life history strategies of a brooding and broadcasting deep-sea asteroid

Combining field and laboratory work, this study investigated the reproductive cycle, aggregative behavior, spawning periodicity, development and early growth of the sea star Henricia lisa living at bathyal depths off eastern Canada. Marked differences were found between individuals from ~1,300 and ~600 m deep. The former had a male biased sex ratio and an aperiodic reproductive cycle, whereas the latter displayed an equal sex ratio and a biannual breeding pattern. Furthermore, the maximum size was larger and female fecundity roughly five times higher in shallower compared to deeper populations. In the tanks, aggregative behavior was recorded twice a year during the summer and winter breeding periods. The onset of aggregations and spawning coincided with a temperature of 3–4°C. Males spawned first and females typically responded inside 30–60 min. Between 12 and 20 eggs were retained to be brooded under the arched arms of the female, whereas the remainder were broadcasted and developed without parental care. The fertilized eggs underwent a first cleavage after 12 h, reached the brachiolaria stage in 1 month, became juveniles within 3–4 months and reached ~ 4 mm in diameter after 14–17 months of growth. The embryos and juveniles developed at the same rate whether brooded or not, and development of winter cohorts was typically slower due to lower prevailing temperatures. This study of H. lisa provides the first evidence of lecithotrophy in a seasonally breeding deep-sea echinoderm and of brooding in a deep-sea asteroid.     

Depth-related shift in life history strategies of a brooding and broadcasting deep-sea asteroid

Combining field and laboratory work, this study investigated the reproductive cycle, aggregative behavior, spawning periodicity, development and early growth of the sea star Henricia lisa living at bathyal depths off eastern Canada. Marked differences were found between individuals from ~1,300 and ~600 m deep. The former had a male biased sex ratio and an aperiodic reproductive cycle, whereas the latter displayed an equal sex ratio and a biannual breeding pattern. Furthermore, the maximum size was larger and female fecundity roughly five times higher in shallower compared to deeper populations. In the tanks, aggregative behavior was recorded twice a year during the summer and winter breeding periods. The onset of aggregations and spawning coincided with a temperature of 3–4°C. Males spawned first and females typically responded inside 30–60 min. Between 12 and 20 eggs were retained to be brooded under the arched arms of the female, whereas the remainder were broadcasted and developed without parental care. The fertilized eggs underwent a first cleavage after 12 h, reached the brachiolaria stage in 1 month, became juveniles within 3–4 months and reached ~ 4 mm in diameter after 14–17 months of growth. The embryos and juveniles developed at the same rate whether brooded or not, and development of winter cohorts was typically slower due to lower prevailing temperatures. This study of H. lisa provides the first evidence of lecithotrophy in a seasonally breeding deep-sea echinoderm and of brooding in a deep-sea asteroid.     

Late Pleistocene dispersal of Indian-Pacific sardine populations in an ancient lineage of the genusSardinops

Temperate sardines fall into two related monotypic genera,Sardina andSardinops. Sardina exists as a cluster of subpopulations in the northeastern Atlantic and Mediterranean, andSardinops encompasses five geographically-isolated regional populations: (1) South Africa-Namibia, (2) Australia-New Zealand, (3) Chile-Peru, (4) Mexico-California and (5) Japan-Russia. We surveyed electrophoretic variability in the products of 34 protein encoding loci inSardina (N=26) and the five Indian-Pacific populations ofSardinops (N=222), collected from 1983 to 1991. Nei's genetic distances () between samples ofSardina andSardinops averaged 1.04 and are typical of distances between species of related genera.s between the regional forms ofSardinops were <-0.011, indicating thatSardinops consists of a single species with widely-scattered subpopulations. Assuming a molecular clock calibrated by the rise of the Panama Isthmus and the opening of the Bering Strait, these genetic distances correspond to times since divergence of <200 000 yr. AlthoughSardinops populations showed a significant degree of allele-frequency heterogeneity (F _ST, a measure of population differentiation, averaged 0.085 over 8 polymorphic loci), the distribution of genetic distances and tests of allele-frequency heterogeneity could not distinguished between hypotheses of north-south antitropical or east-west oceanic dispersal. Low levels of gene diversity inSardinops and mutation-drift disequilibria are consistent with a strong reduction in population size before the Late Pleistocene dispersal to the corners of the Indian-Pacific Oceans of an ancestralSardinops population.     

Shift in nutrient and plankton community in eutrophic lake following introduction of a freshwater bivalve

The impact of the freshwater bivalve Corbicula leana on plankton community dynamics was examined during a cyanobacterial bloom period. Nutrient and chlorophyll concentrations, primary productivity, and phytoplankton and zooplankton communities in the experimental enclosures were measured at 2-3 day intervals. The introduction of mussels reduced net primary productivity and phytoplankton and chlorophyll. Chlorophyll decreased immediately following addition of 100 mussels and then increased over time. After 600 mussels were added, chlorophyll decreased continuously from 87to 25 microg l(-1), approaching that in the mussel-free enclosure. Simultaneously, water transparency increased and concentrations of suspended solids and total phosphorus decreased. Mussel addition caused short-term increases in nutrient concentrations, especially following high-density treatment: phytoplankton density decreased, while cell density in the mussel-free enclosure increased. Zooplankton densities in the two enclosures were similar; however, carbon biomass in the mussel enclosure increased, associated with an increase in large zooplankton. The trophic relationship between phytoplankton and zooplankton was positive in the mussel-free enclosure and negative in the mussel-treatment enclosure, possibly reflecting effects of mussels on both consumer and resource control in the plankton community. Thus, filter feeding by Corbicula affects nutrient recycling and plankton community structure in a freshwater ecosystem through direct feeding and competition for food resources.     

Role of filter-feeding in the nutritional biology of a deep-sea mussel with methanotrophic symbionts

The ability of an undescribed deep-sea hydrocarbon-seep mussel which contains endosymbiotic methanotrophic bacteria to clear, ingest, and assimilate radiolabeled bacteria (Vibrio pelagicus andEscherichia coli) and algae (Dunaliella tertiolecta) was compared with that of the bay musselMytilus edulis. The seep mussel, collected in August 1987 from the Louisana Slope in the Gulf of Mexico, was slower to clear bacteria and algae thanM. edulis. The ingestion and assimilation of filtered bacteria and algae was established from the presence of radiolabel in mussel tissues and feces. The seep mussel was somewhat less efficient in assimilating radiolabeled components from bacteria and algae thanM. edulis. The dietary carbon maintenance-requirement of the seep mussel could potentially be met at environmental concentrations of greater than 10⁶ bacteria ml^–1. At lower concentrations of particulate organic matter, filter-feeding could be an important source of nitrogen and essential nutrients not supplied by the endosymbionts.     

Growth and survivorship in a tidal-flat population of the bivalve Mercenaria mercenaria from Southampton water

A monthly sampling programme was conducted to investigate aspects of the biology of a population of Mercenaria mercenaria (L.) Smooth growth curves were constructed for each year class, and the factors affecting growth rate were considered. Seasonal cycles in flesh weight and calorific content appear to be related to gonal proliferation and subsequent spawning. Recruitment is sporadic and probably depends on the spawning of upstream populations, where conditions are more favourable for larval development. Survivorship curves were constructed for each year class; predation by crabs and gulls appears to account for a large proportion of the observed mortality.     

Transparent exopolymer particles in a deep-sea hydrothermal system: Guaymas Basin,Gulf of California

This is the first report of transparent exopolymer particle (TEP) concentrations within deep-sea hydrothermal vent systems using colorimetric methods, measuring TEP in supernatants of sediments surrounding the vents, in fluids emanating directly from hydrothermal vents and in neutrally buoyant hydrothermal plumes. Samples were collected at Guaymas Basin (Gulf of California), a sedimented hydrothermal system. TEP concentrations within the hydrothermal fluids were significantly greater than the only other report of TEP in deep water. The range of values for TEP abundance were 8–6,451 μg/L of gum xanthan equivalents, the highest values being associated with supernatants of microbial mat-covered sediments. The potential sources and significance of the high concentrations of TEP observed in this deep-sea hydrothermal environment are discussed.     

The relationship between dissolved oxygen concentration and maximum size in deep-sea turrid gastropods: an application of quantile regression

Bathymetric gradients in body size are the most well-known patterns of geographic variation in deep-sea organisms. The causes of size-depth relationships remain uncertain, but most have been attributed to rates of nutrient input. Chapelle and Peck (1999, Nature 399:114-115) recently hypothesized that body size in marine invertebrates is a function of dissolved oxygen concentration. We tested this hypothesis by using quantile regression techniques to assess the relationship of dissolved oxygen levels to maximum size in deep-sea turrid gastropods collected from the North Atlantic. Relationships were examined for a group of nine turrid species and within the abundant lower bathyal species Benthomangelia antonia (Dall, 1881). We controlled the analysis for depth because size in deep-sea gastropods varies bathymetrically. When the effects of depth are accounted for statistically, maximum size in B. antonia increases with increasing levels of dissolved oxygen. In turrids as a group, both depth and oxygen appear to explain significant proportions of the variance in maximum size. These findings suggest that a suite of factors, including dissolved oxygen concentration, may influence maximum size in deep-sea organisms.     

Determinants of social dominance and inheritance of agonistic behavior in an island population of silvereyes,Zosterops lateralis

Summary We examined components of agonistic behavior and dominance in parents and offspring of silvereyes on Heron Island, Great Barrier Reef, to discover their determinants. The data were collected over four years on 1,235 juveniles and their parents. Of four behavioral characters used to compare juveniles and their parents, bill clattering was seen significantly more among young from female parents that exhibited bill clattering. The total absence of submissive behavior and the total absence of aggressive behavior were shown more often than not by young from dominant male parents and subordinate female parents, respectively. Young fledging early in the breeding season tended to be more dominant than those fledging late in the season. The number of brood-mates or the local nest density did not affect the dominance of young. Dominance status appears to be little affected by the performance of parents.     

Phylogeography of Cerastoderma glaucum (Bivalvia: Cardiidae) across Europe: a major break in the Eastern Mediterranean

Molecular variation of the lagoon cockle Cerastoderma glaucum (Poiret, 1789) was examined across the species range along European coasts, from the northern Baltic to the Black Sea and the Caspian Sea. A major phylogeographic break in mitochondrial COI gene sequences (divergence 6.2%) separated a group of Ponto-Caspian and Aegean Sea haplotypes from those to the west of the Peloponnese peninsula in the Mediterranean and in the Atlantic-Baltic sector. A similar subdivision, yet not entirely geographically coincident, was found at 16 allozyme loci (Nei's distance D=0.15). The results imply a long-term isolation of populations in parts of the Eastern Mediterranean or Black Sea basins through the Pleistocene. The subdivision does not concur with previous views on the systematics of C. glaucum complex, but the pattern is notably similar to that described earlier from some fish species. Marked phylogeographic structuring was also found at lower level within the major Mediterranean-Atlantic phylogroup of C. glaucum, which was divided into six regional or local haplotype subgroups. Divergence of these groups may date back one or several major Pleistocene climatic cycles. Local mtDNA diversity was particularly high in a sample from the Ionian Sea, whose mitochondrial identity was of the Mediterranean-Atlantic type, while its nuclear characters were more strongly associated with the Ponto-Caspian type. Patterns of shallower, star-phylogeny type diversity within the Ponto-Caspian phylogroup and in the Baltic Sea area may represent more recent, post-glacial generation of variation.     

Mineralization of major lateral teeth in the radula of a deep-sea hydrothermal vent limpet (Gastropoda:Neolepetopsidae)

Radular teeth of a neolepetopsid patellogastropod limpet, Paralepetopsis ferrugivora, from a deep-sea hydrothermal vent site have similar elemental composition (O, Si, P, S, Cl, K and Fe) to radular teeth of the shallow-waters patellogastropod limpets. However, in contrast to shallow waters limpets, the fully mature teeth of P. ferrugivora do not show any crystalline phases. Amorphous silica was found in the cusp of the teeth and amorphous iron oxide in the junction zone and base of the teeth. Ferritin-rich vesicles were observed in cells adjacent to the junction zone of the early mature teeth, suggesting that these vesicles can mediate the delivery of iron to the tooth matrix. The similarity in the elemental composition between the hydrothermal limpet P. ferrugivora and shallow-waters patellogastropod limpets shows that the extreme hydrothermal environment did not alter the elemental composition of the radular teeth in the deep-sea species.Communicated by P. W. Sammarco, Chauvin     

On the origin of forces in the wake of an elliptical cylinder at low Reynolds number

Environmental Fluid Mechanics - An analysis of forces for flow around an elliptic cylinder at low Reynolds number has been presented in this work. The finite-volume based open source code OpenFOAM...