Evolutionary Toxicology and Transcriptomic Approaches - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 377

natural populations (Bozinovic and Oleksiak 2011). However, although a growing number
of studies provide descriptions of how genes or proteins are altered by chemical stress,
only a few have tried to link these changes to physiological effects (Fent and Sumpter 2011).
Recent analyses conducted on wild fish populations resident in heavily contaminated
estuaries appeared very efficient in exploring the mechanistic basis of resistance to pollut-
ants (Whitehead et al. 2010; Wirgin et al. 2011). These two studies have underlined the major
role played by the AhR in the tolerance of fish to chemical stress. The second study (Wirgin
et al. 2011) showed that the evolved resistance to PCBs that occurs in some populations is
linked to a particular allele of AhR2 encoding an AhR protein characterized by reduced
binding affinity for dioxin-like compounds. Thus, research has clearly shown that a richer
understanding of genome-environment interactions can be derived from studies of natural
populations of outbred species that are routinely exposed to stressors in their environment.
Considering unicellular models, experimental manipulations in microcosms on micro-
algae subjected to petroleum contamination underlined the existence of resistant cells
arising from rare spontaneous mutations that occur randomly before crude oil exposure
(Carrera-Martinez et al. 2010); an adaptation of microalgae to a gradient of continuous
petroleum contamination being clearly detected in a chronically contaminated river
(Carrera-Martinez et al. 2011).
In the general context of global change, aquatic populations are increasingly subjected
to multistress in their natural habitats (including the impacts of toxins, thermal stress,
hypoxia, pathogens). Several studies have suggested that populations subjected to elevated
temperatures may become more susceptible to pollution (Lapointe et al. 2011), and that the
thermal tolerance window is narrowed in ectotherms inhabiting polluted areas compared
with their counterparts in “pristine” environments (Lannig et al. 2008). Furthermore, the
combined effects of parasites and contaminants can reduce either resistance or tolerance
to infection (Marcogliese and Pietrock 2011). The cumulative effects of multiple stressors
could become a priority concern for ecotoxicologists, particularly in their efforts to explore
how adaptation to chronically contaminated habitats could affect the ability of popula-
tions to cope with other stressors. Thus, chemical exposure combined with global warm-
ing may result in evolutionary responses of populations currently not accounted for in any
environmental risk assessment procedure (Messiaen et al. 2010).
Acknowledgment
The authors are much indebted to the excellent field and laboratory assistance of Louis
Quiniou, over 12 years, in the context of several ecotoxicological programs.
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