Biomarkers of Defense, Tolerance, and Ecological Consequences - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 53

organisms display a compensatory adaptive response. The response was confirmed under
field conditions, where an increase in GPx activity was measured after 96 h of exposure
of the gastropods to crude oil fractions, and activities returned to levels close to those of
controls after 2 weeks of exposure (Reid and MacFarlane 2003). This transient GPx activity
response highlights that A. porcata can adapt to stress conditions. Significantly higher lev-
els of GR, GPx, and GST measured in gills of Mytilus galloprovincialis chronically exposed
to metals seem to constitute a specific adaptation in gills to prevent and/or repair metal-
induced damage in cellular components, as no signs of lipid peroxidation were observed
(Fernandez et al. 2010).
Regoli et al. (in Amiard-Triquet et al. 2011) consider that analyses of antioxidants can
be profitably integrated with the measurement of total oxyradical scavenging capacity
(TOSC), which quantifies overall cellular resistance toward different ROS. Compared
to individual defense biomarkers, TOSC is less sensitive but has a greater prognos-
tic value since an impaired capability to neutralize ROS has been associated with the
onset of various forms of oxidative damage such as lysosomal alterations and genotoxic
damage.
Falfushynska et al. (2011, 2012) observed strong differences in the ability of two popula-
tions of gibel carp ( Carassius auratus gibelio ) originating from control or high polluted sites
to withstand additional toxic metal (copper or manganese) or pesticide (thiocarbamate or
tetrazine) exposure. The authors highlighted that fish from the polluted area mobilized
both antioxidant defense and biotransformation systems more effectively than control
fish, despite lower antioxidant defense activities and greater lipid peroxidation dam-
age. These peculiarities could be the result of the adaptation to prolonged life in a toxic
environment. Meyer et al. (2003) demonstrated that larval first- and second-generation
(F1 and F2) offspring of killifish ( Fundulus heteroclitus ) originating from a site highly con-
taminated with PAHs, metals, and pentachlorophenol displayed higher resistance when
exposed in the laboratory to t -butyl hydroperoxide than F1 larvae of control killifish.
Such resistance could be explained by high antioxidant activity levels transmittable to
offspring. However, although the resistance and the adaptation of F. heteroclitus exposed
to contaminated sediments can be explained by higher GPx, GRd, and SOD activity levels
and higher glutathione production rates in exposed adult killifish as compared to control
ones, none of these parameters appears to play a role in acquired resistance. Indeed, only
higher basal levels of glutathione and manganese SOD were measured in F1 and F2 lar-
vae of killifish from the contaminated site as compared to the levels measured in control
F1 larvae in the absence of any exposure to xenobiotics. Thus, Meyer et al. (2003) showed
that, in F. heteroclitus chronically exposed to high pollutant levels, up-regulated antioxi-
dant defenses play a role in both short-term (physiological) and heritable (multigenera-
tional) tolerance of the toxicity of these pollutants, as antioxidant defense capacities could
be transmitted to offspring and lead to long-term genetic adaptation and to resistance
acquired over generations. Comparative studies of different populations of F. heteroclitus
with different physiological tolerances to pollutants have established that neither the level
of gene expression nor the level of DNA polymorphisms was well conserved, because of
the heterogeneity of the stress factors involved coupled with the genetic variation of the
populations (Whitehead et al. 2011). These results suggest that the differential survival of
chronically exposed populations results from genetic adaptation rather than physiologi-
cal acclimation.
Antioxidant defenses vary depending on the season, the nutrient load, and the repro-
ductive cycle of vertebrate and invertebrate aquatic organisms, and it has been established
that antioxidant activity is usually highest in spring and lowest in winter. Organisms