Françoise Denis

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.

Strong and stable environmental structuring of the zooplankton communities in interconnected salt ponds

This study investigated assemblages of Copepoda and Artemia in saltern ponds and determined the main environmental factors affecting them. Copepoda and Artemia were collected from four ponds of varying salinity. Community composition was analyzed relative to environmental variables, with a focus on spatial and seasonal changes. We used a method called Costatis, which is particularly suited to analyze species and environmental data collected at the same sites and dates where the relationships between environmental conditions and composition of biological communities are strong and rather stable, which is the case in our system. The major structuring factors identified by Costatis were salinity and N:P ratio. Cyclopoida and Calanoida were associated with low salinity and low N:P ratios; Harpacticoida were associated with high salinity and high N:P ratios; and Artemia were associated with very high salinity and low N:P ratios. The distribution of these groups over the salinity gradient is in accordance with previous results; the influence of N:P ratio had not been identified before and may reflect specific environmental requirements of the taxa.

Characterization of irritans mariner-like elements in the olive fruit fly Bactrocera oleae (Diptera: Tephritidae): evolutionary implications

Genomic variation among species is commonly driven by transposable element (TE) invasion; thus, the pattern of TEs in a genome allows drawing an evolutionary history of the studied species. This paper reports in vitro and in silico detection and characterization of irritans mariner-like elements (MLEs) in the genome and transcriptome of Bactrocera oleae (Rossi) (Diptera: Tephritidae). Eleven irritans MLE sequences have been isolated in vitro using terminal inverted repeats (TIRs) as primers, and 215 have been extracted in silico from the sequenced genome of B. oleae. Additionally, the sequenced genomes of Bactrocera tryoni (Froggatt) and Bactrocera cucurbitae (Diptera: Tephritidae) have been explored to identify irritans MLEs. A total of 129 sequences from B. tryoni have been extracted, while the genome of B. cucurbitae appears probably devoid of irritans MLEs. All detected irritans MLEs are defective due to several mutations and are clustered together in a monophyletic group suggesting a common ancestor. The evolutionary history and dynamics of these TEs are discussed in relation with the phylogenetic distribution of their hosts. The knowledge on the structure, distribution, dynamic, and evolution of irritans MLEs in Bactrocera species contributes to the understanding of both their evolutionary history and the invasion history of their hosts. This could also be the basis for genetic control strategies using transposable elements.