First insights towards the population genetic structure and the phylogeographic status of the horse mussel (Modiolus barbatus) from the eastern Mediterranean

The horse mussel Modiolus barbatus is a marine benthic bivalve, distributed mainly in the Mediterranean basin, that constitutes a fishery product of high economic importance and a promising candidate for aquaculture. The current study provides the first insights regarding the genetic profile of M. barbatus populations from the eastern Mediterranean, by analysis of a partial segment of the mitochondrial COI gene in individuals collected from five sampling localities within the Aegean Sea. To the best of our knowledge, the derived haplotypes represent the first DNA barcodes of M. barbatus from the entire Mediterranean region. Maximum likelihood phylogenetic analysis revealed that M. barbatus from the North Sea and M. barbatus from the eastern Mediterranean may not belong to the same species and as a consequence, there might be three species of the genus Modiolus in Europe. On the other hand, eastern Mediterranean M. barbatus haplotypes were found to be more closely related to the Asian-Pacific Modiolus species. All geographic populations analysed displayed high levels of genetic diversity, in terms of haplotype and nucleotide diversity and a considerable number of unique alleles. Divergence among populations was found at generally low levels, corresponding with the majority of pairwise Fst values not being significant. These findings suggest no population structure and high levels of gene flow, a common feature observed in marine bivalves with long pelagic larval phases. © Copyright Marine Biological Association of the United Kingdom 2018

Correlation between intermediary metabolism, Hsp gene expression, and oxidative stress-related proteins in long-term thermal-stressed Mytilus galloprovincialis

Long-term exposure of Mytilus galloprovincialis to temperatures beyond 26°C triggers mussel mortality. The present study aimed to integratively illustrate the correlation between intermediary metabolism, hsp gene expression, and oxidative stress-related proteins in long-term thermally stressed Mytilus galloprovincialis and whether they are affected by thermal stress magnitude and duration. We accordingly evaluated the gene expression profiles, in the posterior adductor muscle (PAM) and the mantle, concerning heat shock protein 70 and 90 (hsp70 and hsp90), and the antioxidant defense indicators Mn-SOD, Cu/Zn-SOD, catalase, glutathione S-transferase, and the metallothioneins mt-10 and mt-20. Moreover, we determined antioxidant enzyme activities, oxidative stress through lipid peroxidation, and activities of intermediary metabolism enzymes. The pattern of changes in relative mRNA expression levels indicate that mussels are able to sense thermal stress even when exposed to 22°C and before mussel mortality is initiated. Data indicate a close correlation between the magnitude and duration of thermal stress with lipid peroxidation levels and changes in the activity of antioxidant enzymes and the enzymes of intermediary metabolism. The gene expression and increase in the activities of antioxidant enzymes support a scenario, according to which exposure to 24°C might trigger reactive oxygen species (ROS) production, which is closely correlated with anaerobic metabolism under hypo-metabolic conditions. Increase and maintenance of oxidative stress in conjunction with energy balance disturbance seem to trigger mussel mortality after long-term exposure at temperatures beyond 26°C. Eventually, in the context of preparation for oxidative stress, certain hypotheses and models are suggested, integrating the several steps of cellular stress response. Copyright © 2020 the American Physiological Societ