C.S.I. on the Deep Reef (Chemotrophic Species Investigations)

In this lesson students discover what factors are indicative of chemotrophic nutritional strategies. Students will be able to describe at least three chemotrophic symbioses known from deep-sea habitats. They will identify and explain three indicators of chemotropic nutrition. This hands-on activity uses online data resources and includes: focus questions, background information, evaluations and extensions, as well as resources and student handouts. Educational levels: High school

Drilling predation on bivalve shell assemblages at Playa Guardalavaca, Cuba

Drilling predation plays an important role in the evolution and diversification of organisms, and is one of the most studied biotic interactions in fossil and modern records. Marks of drilling predation on mollusc shells are proof of food activity and the selective pressure of one taxon on another. In this study, we explore drilling predation on preserved bivalve death assemblages (thanatocoenosis) at Playa Guardalavaca, Cuba. We characterize the taxonomic composition, relative abundance and incidence of drilling. Furthermore, geometric morphometric tools were used to test whether there was a preference for any particular form of shell. Forty-eight species were identified, and a little less than half (21) showed drilling predation marks. The families with the highest species richness were Lucinidae and Tellinidae, with 11 species each. A total of 1,726 valves were quantified, estimating an abundance of 863 specimens. 190 valves showed drilling marks (22% of the abundance). The most abundant species were Lucina sp. (464 shells), Divalinga quadrisulcata (328), Americardia media (242), Ctena imbricatula (156), and Chione spp. (117). However, the most predated species were Epicodakia sp. (100%), Acorylus gouldii (56%), and Eurytellina sp. (44%). The highest predation rate occurs on small and medium-sized valves (≤ 7 mm); however, according to the Kolmogorov-Smirnov test, this result is only statistically significative in Lucina sp. (p ˂ 0.001). The morphometric analysis showed predation preferences for species with semi-circular rather than elliptical shells. These results elucidate that drilling predation on bivalves is not only determined by the abundance of prey, but also by their external morphology and size, suggesting highly specialised feeding behaviour by predators.his research was partially financed by the projects 'VLIR P1. Valorisation of environmental scientific services for climate stress mitigation in eastern of Cuba' (Universidad de Oriente, Cuba), 'Project P1 - Risk mitigation plan for biodiversity and food production to face climatic change in the eastern region of Cuba' (Universidad de Oriente – VLIR, Belgium), and the grant from CONICET, Argentina (PIP 11220170100080

Estimating Evolutionary Volatility in a Maximum-Likelihood Framework

Evolutionary volatility is a trait that encompasses a clade’s combined capacity for origination and extinction. High volatility increases extinction risk, and declining global extinction rates are thought to be linked to declining volatility. Despite volatility’s scientific importance, there is no standardized way of measuring it. This study provides a new method, derived from a stochastic birth-death model, of estimating evolutionary volatility from fossil data. Simulations indicate that the method produces accurate and precise estimates for large fossil datasets. Analysis of fossil data for five bivalve families (Lucinidae, Mytilidae, Pectinidae, Pholadomyidae, and Veneridae) indicates that diversity projections made from the estimates lack precision and do not capture important aspects of the data. However, this method of estimating volatility serves as a simple and computationally efficient null model for comparisons against more complex hypotheses

Kepadatan kerang lumpur Anodontia edentula Linnaeus, 1758 kaitannya dengan parameter lingkungan di Kabupaten Muna

The research aims to analyze the density of mud clams Anodintia edentula Linnaeus, 1758 relation to environmental parameters, covering organic material content and composition of sediment in Muna regency. Research carried out in coastal Lambiku and Tobea Island. The sample collection begins in March until May 2011, intervals collection example once a month for three months. A collection of mud clams example in a plot trasek (Line Transect Plot) is determined (purposive sampling). A plot observation based on three categories, Plot I near coast, Plot II the transition and Plot III far from the beach, intervals 50m each a plot observation. Analysis data the density use Krebs (1978) formula, relations of density and environmental parameters use corelation and descriptif analysis. The research results show that the density is different of mud clams between Tobea Island and coastal Lambiku. The density of mud clams on the Tobea Island have higher is 33 ind m-2 or 29-40 ind m-2. While density of mud clams in coast Lambiku is 10 ind m-2 or 8-11 ind m-2. The density of mud clams far from the beach between the coastal areas relatively different. While composition sediment and the organic matter on Tobea Island and coastal Lambiku relatively is the same. Phosphates and sulphur concentration on the Tobea island each of 13,90 ppm and 15,76 ppm. Phosphates and sulphur concentration in coastal Lambiku each of 14,55 ppm and 17,01 ppm. Phosphate and sulfur concentrate far from shore show organic material content of sulphur and phosphates is high with density mud clams

An overview of chemosynthetic symbioses in bivalves from the North Atlantic and Mediterranean Sea

Deep-sea bivalves found at hydrothermal vents, cold seeps and organic falls are sustained by chemosynthetic bacteria that ensure part or all of their carbon nutrition. These symbioses are of prime importance for the functioning of the ecosystems. Similar symbioses occur in other bivalve species living in shallow and coastal reduced habitats worldwide. In recent years, several deep-sea species have been investigated from continental margins around Europe, West Africa, eastern Americas, the Gulf of Mexico, and from hydrothermal vents on the Mid-Atlantic Ridge. In parallel, numerous, more easily accessible shallow marine species have been studied. Herein we provide a summary of the current knowledge available on chemosymbiotic bivalves in the area ranging west-to-east from the Gulf of Mexico to the Sea of Marmara, and north-to-south from the Arctic to the Gulf of Guinea. Characteristics of symbioses in 53 species from the area are summarized for each of the five bivalve families documented to harbor chemosynthetic symbionts (Mytilidae, Vesicomyidae, Solemyidae, Thyasiridae and Lucinidae). Comparisons are made between the families, with special emphasis on ecology, life cycle, and connectivity. Chemosynthetic symbioses are a major adaptation to ecosystems and habitats exposed to reducing conditions. However, relatively little is known regarding their diversity and functioning, apart from a few “model species” on which effort has focused over the last 30 yr. In the context of increasing concern about biodiversity and ecosystems, and increasing anthropogenic pressure on oceans, we advocate a better assessment of the diversity of bivalve symbioses in order to evaluate the capacities of these remarkable ecological and evolutionary units to withstand environmental change

On the evolutionary ecology of symbioses between chemosynthetic bacteria and bivalves

Mutualistic associations between bacteria and eukaryotes occur ubiquitously in nature, forming the basis for key ecological and evolutionary innovations. Some of the most prominent examples of these symbioses are chemosynthetic bacteria and marine invertebrates living in the absence of sunlight at deep-sea hydrothermal vents and in sediments rich in reduced sulfur compounds. Here, chemosynthetic bacteria living in close association with their hosts convert CO2 or CH4 into organic compounds and provide the host with necessary nutrients. The dominant macrofauna of hydrothermal vent and cold seep ecosystems all depend on the metabolic activity of chemosynthetic bacteria, which accounts for almost all primary production in these complex ecosystems. Many of these enigmatic mutualistic associations are found within the molluscan class Bivalvia. Currently, chemosynthetic symbioses have been reported from five distinct bivalve families (Lucinidae, Mytilidae, Solemyidae, Thyasiridae, and Vesicomyidae). This brief review aims to provide an overview of the diverse physiological and genetic adaptations of symbiotic chemosynthetic bacteria and their bivalve hosts

Global biogeography of chemosynthetic symbionts reveals both localized and globally distributed

In the ocean, most hosts acquire their symbionts from the environment. Due to the immense spatial scales involved, our understanding of the biogeography of hosts and symbionts in marine systems is patchy, although this knowledge is essential for understanding fundamental aspects of symbiosis such as host-symbiont specificity and evolution. Lucinidae is the most species-rich and widely distributed family of marine bivalves hosting autotrophic bacterial endosymbionts. Previous molecular surveys identified location-specific symbiont types that "promiscuously" form associations with multiple divergent cooccurring host species. This flexibility of host-microbe pairings is thought to underpin their global success, as it allows hosts to form associations with locally adapted symbionts. We used metagenomics to investigate the biodiversity, functional variability, and genetic exchange among the endosymbionts of 12 lucinid host species from across the globe. We report a cosmopolitan symbiont species, Candidatus Thiodiazotropha taylori, associated with multiple lucinid host species. Ca. T. taylori has achieved more success at dispersal and establishing symbioses with lucinids than any other symbiont described thus far. This discovery challenges our understanding of symbiont dispersal and location-specific colonization and suggests both symbiont and host flexibility underpin the ecological and evolutionary success of the lucinid symbiosis

Taxonomic, Genetic and Functional Diversity of Symbionts Associated with the Coastal Bivalve Family Lucinidae

Extant bivalve members from the family Lucinidae harbor chemosynthetic gammaproteobacterial gill endosymbionts capable of thioautotrophy. These endosymbionts are environmentally acquired and belong to a paraphyletic group distantly related to other marine chemosymbionts. In coastal habitats, lucinid chemosymbionts participate in facilitative interactions with their hosts and surrounding seagrass habitat that results in symbiotic sulfide detoxification, oxygen release from seagrass roots, carbon fixation, and/or symbiotic nitrogen fixation. Currently, the structural and functional complexity of whole lucinid gill microbiomes, as well as their interactions with lucinid bivalves and their surrounding environment, have not been comprehensively characterized. This dissertation focuses on the taxonomic, genetic, and functional diversity in the gill microbiomes of three Floridian coastal lucinid bivalve species, Phacoides pectinatus, Ctena orbiculata, and Stewartia floridana, in the context of environmental data where appropriate. Analyses of these lucinid gill microbiomes showed taxonomic diversity that was unaffected by spatial distribution patterns. Phacoides pectinatus gill microbiomes sampled from a coastal mangrove habitat contained, in order of relative abundances, a chemosynthetic symbiont species that was taxonomically and functionally distinct from seagrass-associated chemosynthetic lucinid symbionts, a heterotrophic Kistimonas-like species, and a heterotrophic Spirochaeta-like species. In comparison, gill microbiomes of a seagrass-dwelling C. orbiculata population comprised four strains of chemosymbionts that belonged to two separate species and low abundances of an uncharacterized Endozoicomonas-like operational taxonomy unit (OTU). Gill microbiomes of a separate seagrass-dwelling S. floridana population consisted of another chemosynthetic symbiont species and low abundances of a heterotrophic Spirochaeta-like species that was distantly related to the Spirochaeta-like species in P. pectinatus. Functional characterization of host- and microbiome-related genes/transcripts in these bivalve species revealed previously unreported C1-compound oxidation functions in some chemosymbionts and other functions relevant to microbe-microbe competition, symbiont selection, metabolism support, and symbiont-to-host nutrient transfer. Preliminary differential expression analyses on host- and microbiome genes across micro-habitats with different vegetation coverages showed potential upregulation of C. orbiculata functions involved in aerobic respiration, aerobic stress, electron transport, and mitochondrial sulfide detoxification, as well as downregulation of a sulfurtransferase gene encoded by its chemosynthetic symbionts, in a seagrass-covered quadrat compared to an algae-covered quadrat. In comparison, very few genes mappable to S. floridana and its chemosymbiont were differentially expressed between predominantly sand-covered and seagrass-covered quadrats, but the Spirochaeta-like species over-expressed carbon, nitrogen, phosphate, transport, synthesis, transcriptional regulation, and protein degradation functions in predominantly sand-covered quadrats. These findings reaffirm the overlooked notion of heterogeneous lucinid gill microbiomes that can vary within and between host species and populations. At the same time, this project advances understanding of the functional diversity across chemosynthetic lucinid symbionts and offers insights on lucinid-microbiome-environment interactions

Microbial communities in developmental stages of lucinid bivalves

Bivalves from the family Lucinidae host sulfur-oxidizing bacterial symbionts, which are housed inside specialized gill epithelial cells and are assumed to be acquired from the environment. However, little is known about the Lucinidae life cycle and symbiont acquisition in the wild. Some lucinid species broadcast their gametes into the surrounding water column, however, a few have been found to externally brood their offspring by the forming gelatinous egg masses. So far, symbiont transmission has only been investigated in one species that reproduces via broadcast spawning. Here, we show that the lucinid Loripes orbiculatus from the West African coast forms egg masses and these are dominated by diverse members of the Alphaproteobacteria, Clostridia, and Gammaproteobacteria. The microbial communities of the egg masses were distinct from those in the environments surrounding lucinids, indicating that larvae may shape their associated microbiomes. The gill symbiont of the adults was undetectable in the developmental stages, supporting horizontal transmission of the symbiont with environmental symbiont acquisition after hatching from the egg masses. These results demonstrate that L. orbiculatus acquires symbionts from the environment independent of the host’s reproductive strategy (brooding or broadcast spawning) and reveal previously unknown associations with microbes during lucinid early development