Marine Ecosystems under Toxic Pressure - Vulnerability of Coastal Ecosystems and Adaptation - page 31

genetic adaptation rather than to physiological acclimatization
[BUR 07, VAN 08].
The energy an organism allots to developing its resistance to stress
increases its probability of survival, but can have repercussions for the
energy necessary for essential functions such as growth and
reproduction. These energetic compromises between maintenance
(survival) and production (measured, for example, by the rate of
development and fertility) are found in populations subjected to
chemical stress [MOU 11]. In their summary on the cost of tolerance
to toxins, measured by experimental approaches, Van den Brink
[VAN 00] have underlined the cost of tolerance to metals in plants, of
invertebrates and fish, which show modifications in the traits of their
life history. Arthropods' resistant to insecticides show a cost that is
characterized by a loss of physiological performance in terms of
fecundity, rates of development and fertility [ROU 87].
Several studies, carried out in laboratories, based on the successive
generations of fish selected for their resistance to contamination, have
typified the cost of resistance, showing:
- a reduction in the size of the offspring, a weaker fecundity and
increase in the age of first maturity, for fish exposed to cadmium
compared to control fish [XIE 04];
- a greater vulnerability in fish exposed to contaminated estuary
sediments compared to control fish faced with other stress factors such
as ultraviolet (UV) radiation and hypoxia [MEY 03];
-in the case of flounder ( P. flesus ), resistant genotypes,
characterized by their significant capacity to maintain the integrity of
their DNA in polluted estuaries, have shown a reduced fecundity and a
weaker condition index [MAR 04].
Different molecular mechanisms for resisting toxins, therefore,
generate energy costs that can affect essential physiological functions
[TAY 96]. However, the majority of studies carried out in this domain
were performed with experimental measurement in laboratory, and a
major question remains: what is the validity of costs estimated in a
laboratory, in a natural environment?