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10.5 Conclusions
Older papers dealing with behavioral effects of chemicals were mainly based on acute
exposures responsible for short-term effects (Eisler 2000; Grue
et al. in Dell'Omo 2002).
Behavioral responses are much more sensitive to chemical stress than lethal responses. On
the other hand, they are not more sensitive than biochemical or physiological biomarkers
classically proposed for environmental biomonitoring. This seems logical since a number
of these biomarkers have a causal relationship with behavioral alterations. From the pres-
ent review, it appears that these alterations may be induced at experimental concentra-
tions that are realistic in comparison to those encountered in contaminated environments,
including chronic exposures in the wild. In addition, good consistency has been shown
between experimental and field studies, suggesting that extrapolation from the labora-
tory to the wild is not inappropriate, even if a cautious approach remains necessary. It is
important to consider that, under experimental conditions, organisms are subjected to an
unavoidable exposure, whereas in the natural environment, they may be able to avoid con-
taminated water masses, sediment, or food. It would be unwise, however, to consider that
all populations will be able to flee polluted environments. It is also indispensable to take
into account indirect effects that can occur in a polluted environment such as prey-preda-
tor interactions and competitive interactions between species (Lefcort et al. 1999 literature
cited therein; Fleeger et al. 2003). The influence of abiotic factors (light, temperature, sea-
son) is also important (Triebskorn et al. 1997; Scherer and McNicol 1998). Moreover, natural
environments are rarely exposed to only one kind of contaminant, and taking into account
interactions between chemicals in mixtures is one of the major challenges for the future
of ecotoxicology.
The use of behavioral biomarkers in the assessment of environmental risk is also lim-
ited because discrepancies exist between the effects of different contaminants at different
levels of biological organization in different species. In many cases, discrepancies may
result from acute versus chronic conditions of exposure. There is agreement in the litera-
ture to consider that organisms can adapt to chronic exposure since they have time to put
into place efficient mechanisms of detoxification (Chapter 3), whereas in acute tests these
mechanisms are immediately overwhelmed. This explanation is not always satisfactory,
and behavioral ecotoxicology—as with other fields of ecotoxicology—suffers from a lack
of fundamental research, most of the known mechanistic bases being derived from those
elucidated in birds and mammals.
More precisely, the extrapolation of observations from one species in the laboratory to
multiple species in the wild requires an understanding of the factors governing inherent
sensitivity (e.g., Scarfe et al. 1982; Keizer
et al. 1995). Because it is impossible to obtain a
complete set of data for most species, behavioral ecotoxicologists must focus on a certain
number of sentinel species, chosen according to criteria that are at least partly relevant in
other fields of ecotoxicology (Chapter 7).
Despite these limitations, we can agree with Roast et al. (2000) in their claim that behav-
ioral studies provide a better understanding of chemical impacts than lethal effects, par-
ticularly if behavior is altered at realistic doses. Behavior is an individual response that
has clear links with biochemical and physiological responses (providing early warning
biomarkers) on the one hand, and population effects resulting from reduced longevity and
reduced reproductive success (ecologically relevant biomarkers) on the other hand. Many
studies dealing with relationships between infra-individual impairments and behavioral
changes are available, but few investigations have been devoted to the consequences of
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