Marine Ecosystems under Toxic Pressure - Vulnerability of Coastal Ecosystems and Adaptation - page 26

mitochondrial genetic diversity observed in populations of cat-fish
( Ameiurus nebulosus ) taken from contaminated sites. These selective
pressures can lead to changes in the distribution frequencies of alleles
and genotypes in exposed populations [HEI 97, MAR 03, MUL 02,
VIR 03]. Analyses of persistent fish populations surviving in
chronically contaminated estuaries for more than 60 years in the
United States and Europe, compared to populations living in
untouched estuaries, have furnished new information on the
identification of candidate genes potentially implicated in the response
of the fish to chemical agents [HAH 04, HAH 05, MAR 10]. Thus,
Hemmer-Hansen et al . [HEM 07] have demonstrated the flounder's
excellent capacity to adapt ( Platichthys flesus ) to contrasting
environments in estuaries. They have underlined the genetic base of
these species' adaptation to the particular environment of the Baltic
Sea compared to the North Sea (salinity gradient, chemical stress,
hypoxia, etc.). Later on, different studies carried out on populations of
flounder in estuaries confirmed these results [LAR 02, MAR 03,
MAR 04]. The authors found a greater capacity to maintain the
integrity of DNA among individuals carrying the allele PGM-85 in
different estuaries contaminated along the Atlantic Coast of France
(the estuaries of the Loire, Seine and Vilaine), compared to an
uncontaminated control estuary (Ster); the hypothesis of selective
pressure acting on the locus PGM has been formulated. Associations
(genotype-phenotype) have been observed for several aquatic species
exposed to diverse contaminants [GIL 99, KAM 00 VAN 00,
WEI 02]. Correlations between individual heterozygosis and fitness
components (such as survival, stability of development, growth rate,
fecundity and metabolism) have been observed among different
aquatic species exposed to contamination. [BEN 92, GIL 99, HAR 04,
KOP 92, MAR 03, MAR 04] have observed that flounder displaying
the greatest genetic variability (the most heterozygotic) were also the
most capable of maintaining DNA integrity in the contaminated
estuaries, confirming the conclusions of several studies carried out on
natural fish populations exposed to complex mixtures of contaminants
[LAR 01, LAR 02]. These correlations can in part be explained by a
slower base metabolism among the heterozygotic individuals, thus
leading to a smaller energy need for vital functions and finally to an