Genetic polymorphism and its potential relation to environmental stress in five populations of the European flounder Platichthys flesus, along the French Atlantic coast.

In this study, new DNA markers were explored for the flounder Platichthys flesus. cDNA and genomic sequences of the genes encoding the glyceraldehyde-3-phosphate-deshydrogenase (GAPDH), the cytosolic creatine kinase (CK), the prostaglandin D synthase (PGDS) and the betaine homocysteine methyltransferase (BHMT) were characterized. The tumour suppressor p53 gene structure was already described. A PCR-SSCP (Single Strand Conformation Polymorphism) analysis was finally conducted to study the genetic polymorphism of different populations of flounders collected along the French Atlantic coast. Four highly contaminated French estuaries (Seine, Vilaine, Loire and Gironde) were sampled and compared to a reference estuary (Ster) to explore possible selective effect of the environment on specific allelic frequencies. Our results showed that two loci p53 and PGDS, could be potential markers of chemical stress: p53A allele frequency increased in contaminated systems compared to the reference system. In the Vilaine estuary, PGDS polymorphism could be related to pesticide stress.

Molecular identification and expression of differentially regulated genes of the European flounder, Platichthys flesus, submitted to pesticide exposure.

Effects of pesticide exposure on the European flounder, Platichthys flesus, were investigated using a suppression subtractive hybridization method (SSH) to identify up- and down-regulated genes after a 30-day exposure to herbicides (a cocktail of atrazine, diuron, and isoproturon, and a single herbicide, glyphosate). A total of 256 expressed gene sequences were identified as having the potential for being differentially expressed, of which 116 could be identified by homology with databased sequences. The metabolic functions with which they are associated include energy production, general metabolism, signaling, transport, immune system, and structure. Expression of 14 of these genes was analyzed in liver, muscle, and gills by reverse transcriptase-polymerase chain reaction (RT-PCR) under experimental conditions (0, 15, and 30 days of exposure) and under field conditions (sampling in two estuaries displaying different levels of pesticide contamination). This study provides a first basis for studying the response of fish to pesticide exposure and allows the characterization of new potential genetic markers of pesticide contamination in the field.

Discrepancies in phylogeographical patterns of two European anglerfishes (Lophius budegassa and Lophius piscatorius).

In order to investigate the relative importance of historical processes and life-history traits in shaping the present-day genetic structure of European anglerfishes, 382 Lophius piscatorius and 134 Lophius budegassa were sequenced on the 5' end of the mitochondrial control region. Both species showed a limited genetic structure and some evidence of a demographic expansion that probably occurred not at the end of the Last Glacial Maximum, but earlier in the Pleistocene. The main discrepancy between the two anglerfishes concerned the genetic structure between Atlantic and Mediterranean populations, with weak but significant differentiation observed only in L. budegassa. This genetic structure was congruent with the existence of a phylogeographical break previously reported in several marine species across the Almeria-Oran front. The contrast observed between both anglerfishes was supposed to be induced by a possible more ancient (re)colonisation of the Mediterranean Sea by L. budegassa. Finally, the limited genetic structure and lack of isolation by distance observed in both species suggested high larval dispersal capacities that probably overwhelm the influence of the bathymetric distribution range on migrations of adults and juveniles.