Dario Moraga

Rapid mitochondrial adjustments in response to short-term hypoxia and re-oxygenation in the Pacific oyster Crassostrea gigas

SUMMARY As oxygen concentrations in marine coastal habitats can fluctuate rapidly and drastically, sessile marine organisms such as the oyster Crassostrea gigas can experience marked and rapid oxygen variations. In this study, we investigated the responses of oyster gill mitochondria to short-term hypoxia (3 and 12 h, at 1.7 mg O2 l−1) and subsequent re-oxygenation. Mitochondrial respiratory rates (states 3 and 4 stimulated by glutamate) and phosphorylation efficiency [respiratory control ratio (RCR) and the relationship between ADP and oxygen consumption (ADP/O)] were measured. Cytochrome c oxidase (CCO) activity and cytochrome concentrations (a, b, c1 and c) were measured to investigate the rearrangements of respiratory chain subunits. The potential implication of an alternative oxidase (AOX) was investigated using an inhibitor of the respiratory chain (antimycin A) and through gene expression analysis in gills and digestive gland. Results indicate a downregulation of mitochondrial capacity, with 60% inhibition of respiratory rates after 12 h of hypoxia. RCR remained stable, while ADP/O increased after 12 h of hypoxia and 1 h of re-oxygenation, suggesting increased phosphorylation efficiency. CCO showed a fast and remarkable increase of its catalytic activity only after 3 h of hypoxia. AOX mRNA levels showed similar patterns in gills and digestive gland, and were upregulated after 12 and 24 h of hypoxia and during re-oxygenation. Results suggest a set of controls regulating mitochondrial functions in response to oxygen fluctuations, and demonstrate the fast and extreme plasticity of oyster mitochondria in response to oxygen variations.

Genetic separation of two allopatric populations of hydrothermal snails Alviniconcha spp. (Gastropoda) from two South Western Pacific back-arc basins

Abstract Communities of organisms associated with back-arc basin hot vents in the South West Pacific are dominated in biomass by gastropods. Alviniconcha hessleri (Okutani and Ohta, 1988) was recovered for the first time from the Marianas basin. Morphologically and anatomically similar gastropods have been collected from the North Fiji and Lau basins and seem to belong to the same genus. However, genetic data suggest that these two forms of Alviniconcha spp. are genetically distinct from each other. In spite of having planktonotrophic larvae, these populations do not show genetic exchange and therefore are genetically isolated. Founder effects, the tectonic isolation of the two basins and the ecological specificities of the two vents could explain this strong genetic differentiation found between these two allopatric populations of Alviniconcha spp.

Genetic differentiation across the Western Pacific populations of the hydrothermal vent bivalve Bathymodiolus spp. and the Eastern Pacific (13°N) population of Bathymodiolus thermophilus

Abstract Deep-sea mussels, closely related to the Bathymodiolus genus and individuals of Bathymodiolus thermophilus , were collected on hydrothermal vents of the Lau and North-Fiji back-arc basins (Western Pacific) and at 13°N on the East Pacific Rise, respectively. Separate tissue homogenates were submitted to starch gel electrophoresis in order to study the genetic structure of the populations at 11 enzyme loci. Significant departures from the Hardy-Weinberg equilibrium were found at Aat -1, Gpi and Pgm loci without any location specificity. All the observed departures corresponded to heterozygote deficiencies that are common in mollusc bivalves. The genetic variability of these mussels was low in all samples, especially for the North-Fiji population. The genetic distances measured between populations demonstrated that significant genetic differentiation occurs between the Western Pacific mussel populations and the Eastern Pacific B. thermophilus , whereas gene flow appeared to be maintained between the two back-arc basins. The presence of both shared heterozygotes and genetic distances found between the western and the eastern populations do not allow us to separate these allopatric forms as distinct sibling species.

Genetic variability of the Lucinidae:Loripes lucinalis,Lucinella divaricata and Lucinoma borealis minor (Mollusca: Bivalvia) from Brittany, France

Abstract Genetic structure of the Lucinidae ( Loripes lucinalis , Lucinella divaricata and Lucinoma borealis minor) was analysed from allozymic data of samples collected in Brittany. The results obtained show a high interpopulational genetic variability; its level varies from 0.62 to 0.77 for polymorphism and from 0.20 to 0.43 for heterozygosity. The particular alleles of each species and a diagnostic locus of L. lucinalis are revealed. Genetic differences between species were evaluated by a multivariate analysis applied to electromorphs and by the genetic distances index.