Biology Reference
In-Depth Information
distributed. The relationship between steroid hormones and behavior is well established
in different fish species (Bjerselius et al. 2001; Sisneros et al. 2004; Knapp and Neff 2006).
However, the mechanisms behind these observations are not clearly understood and gen-
erally are extrapolated from studies with birds and mammals.
Thyroid hormones are essential for the normal development of brain, and mamma-
lian studies have shown that alterations of concentrations of these hormones have conse-
quences on neurobehavioral development and neurotransmitter levels. A study dealing
with European eel
Anguilla anguilla
upstream migration suggested that the thyrotropic
axis was activated during the colonization of river habitats by elvers (Imbert et al. 2008).
Juvenile specimens of Atlantic salmon
Salmo salar
exposed to PCB (Aroclor 1254 at 1 or 10
μg L
-1
) during smolting exhibit a dose-dependent reduction in preference for seawater. In
parallel, plasma triiodothyronine was reduced 35-50%, whereas plasma thyroxine was
unaffected (Lerner et al. 2007). Impairment of thyroid function could contribute to behav-
ioral disturbances observed in the estuarine fish
F. heteroclitus
from a contaminated estu-
ary (Weis et al. 2001). In the Atlantic cod
Gadus morhua
, altered thyroid function has been
shown to influence spontaneous activity and feeding (Castonguay and Cyr 1998, quoted
by Weis et al. 2001). In zebrafish (
Danio rerio
) embryos waterborne exposed to BDE-47 at
1.25, 5, and 20 µM starting from 6 h post-fertilization (hpf), Chen et al. 2012 showed an
inhibition of the axonal growth of primary and secondary motor neurons during the early
developmental stages, suggesting the functional relevance of structural changes, in agree-
ment with impaired motor behavior.
10.2.3 Energy Metabolism Impairments
Many studies have shown a link between the ability of animals to perform normal behav-
ior in polluted media and several aspects of energy metabolism. In fish, a review by Scott
and Sloman (2004) indicates that different metals and numerous pesticides are responsible
for alteration in metabolic substrate levels, a pattern that could result from enzymatic sys-
tem dysfunction (enzymes involved in carbohydrate and/or protein metabolism). These
metabolic impairments result in alterations of maintenance (changes in oxygen consump-
tion and ventilation rate) and reduced swimming performance.
In trout (
Salmo trutta
fario
) exposed for several weeks in water diverted from two pol-
luted streams (bypass systems) in the field, biomarkers were determined at different levels
of biological organization (swimming behavior, stress protein concentrations, liver ultra-
structure). Swimming velocity significantly dropped in trout in the most polluted stream,
perhaps as a consequence of less energy being available for locomotion. In agreement with
an increasing number of mitochondria and a depletion of glycogen storage in the liver,
catabolic, energy-providing mechanisms were activated (Triebskorn et al. 1997). In the rag-
worm
Hediste (Nereis) diversicolor
exposed in the field or in the laboratory to contaminated
sediment, Moreira et al. (2006a) have shown a depletion of the post-exposure feeding rate
associated with increased lactate dehydrogenase activity that reveals an increased con-
tribution of anaerobic metabolism. This metabolic change suggests an urgent need for
additional energy to ameliorate chemical stress.
Coping with toxicants has an associated metabolic cost (Mouneyrac et al. in Amiard-
Triquet et al. 2011). The relationship between behavioral and metabolic disruption is
depicted in Figure 10.3 in the case of invertebrates exposed to increasing levels of metals.
At low exposure, crustaceans are able to detoxify absorbed metals, but behaviors with
a high energy cost are significantly impaired. With increasing exposure, the detoxifica-
tion capacity of metallothioneins is overwhelmed, and this results in increasing metal
Search WWH ::
Custom Search