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between allelic or genotypic frequencies and chemical contamination but did not explore
how chemical stress can select different genetic variants. Examples cited below integrate
individual physiological performances (phenotypes) in order to establish “genotype-pheno-
type” relations, for example, differential genotype sensitivity to pollutants. The first studies
performed in this way were carried out essentially in the laboratory. For example, differ-
ential mortalities associated with particular alleles or genotypes at the loci PGM and PGI
(phosphoglucose isomerase) were observed in fish exposed to experimental metal contami-
nation (see the synthesis of Gillepsie and Guttman 1999). More recently, Virgilio et al. (2005)
highlighted robust relations between genetic variability at several allozyme loci and differ-
ential mortality during exposure to copper, whatever the site of origin of the population of
the estuarine polychaete
Hediste diversicolor
examined. More directly, Chagnon and Guttman
(1989) found in the mosquitofish
Gambusia
affinis
different enzyme activities between allelic
variants at the PGM locus, suggesting the existence of a tolerant allele to copper and a more
sensitive one. In the same species and studying exposure to mercury, Kramer et al. (1992)
have highlighted differential metabolic activities between individuals carrying differ-
ent genotypes at the PGI locus. In a recent analysis, a genotype-dependent recovery was
detected from acute exposure to trace metal contamination in the freshwater clam
Sphaerium
novaezelandiae
(Philips and Hickey 2010); no significant genotype-specific differences in
mortality were detected, considering particularly the allozyme PGM, but the authors did
identify differences in reburial rates across all genotypes. In this experiment, the popula-
tions display genetically based variation in their ability to recover from zinc exposure in the
laboratory and that such variation is linked to a physiological trait (reburial).
Other studies coupling genotypes and phenotypes have been performed but this time
with individuals collected in the field. Their objectives were to detect differential physi-
ological responses measured in the organisms directly after collection. Theodorakis and
Shugart (1997) identified an increase in the frequency of particular RAPD bands in individ-
uals from two natural populations of
Gambusia affinis
exposed to radionuclides, compared
to a reference population; individuals carrying these particular bands also had better fecun-
dity, a lower level of DNA damage and better survival compared to the others (Theodorakis
and Shugart 1997, 1999). The authors hypothesized that these bands may be linked to loci
involved in the protection of macromolecules or in the reparation of cellular and molecu-
lar lesions (Theodorakis and Shugart 1999). Larno et al. (2001) showed in highly polluted
populations of chub (
Leuciscus cephalus
) from different rivers of the Rhône basin, that par-
ticular alleles or genotypes at the PGM and EST (esterase) loci were correlated to higher
DNA integrities. They also found an increase in frequency of these alleles or genotypes
with the intensity of contamination, leading thus to the description of alleles as potentially
“tolerant” to contamination (Larno et al. 2001). Different studies performed on estuarine
populations of flounder (
Platichthys flesus)
) have confirmed previous findings (Laroche et al.
2002; Marchand et al. 2003, 2004). The authors found a better ability to maintain DNA integ-
rity in individual flounders carrying the PGM-85 allele in different contaminated estuaries
along the Atlantic coast of France (Loire, Seine, and Vilaine estuaries), compared to a refer-
ence estuary (Ster); a higher frequency of the PGM-85 allele was detected in populations
from contaminated estuaries and the hypothesis of a selective pressure acting on the PGM
locus was formulated. Such associations (genotype-phenotype) have also been observed
for several aquatic species exposed to various contaminants (Gillepsie and Guttman 1999;
Kammenga et al. 2000; Van Straalen and Hoffman 2000; Weis 2002).
Correlations between individual heterozygosity (essentially estimated with allozyme
markers) and particular fitness components (survival, development stability, growth rate,
fecundity, metabolism, etc.) have been observed in different aquatic species exposed to
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