Chemistry Reference
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well as in learning and memory in the honeybee. Again, effects of this kind can have
a detrimental impact on foraging.
Behavioral effects of pollutants may also disrupt reproduction. In principle, it
seems reasonable to suppose that behavioral effects upon birds may lead to distur-
bances of pairing or mating, nest desertion, incubation of eggs, or failure to protect
nest and young, although there is a shortage of solid evidence for this happening in
the natural world. In one study with four different species of ducks (Brewer et al.
1988), application of methyl parathion led to reduced survival of ducklings, and this
was attributed to brood abandonment. Exposure to sublethal levels of methylmer-
cury has sometimes been associated with behavioral effects and reduced reproduc-
tive success in birds (see Chapter 8 of this topic). In a study of common loons in
North America, there was evidence of aberrant breeding behavior (e.g., reduced nest
occupancy) that was related to levels of exposure to this pollutant. There was also
evidence of reduced reproductive success related to methylmercury exposure in the
same population (Evers et al. 2008).
Another adverse behavioral effect of neurotoxic compounds can be reduced abil-
ity to avoid predation. In a study of predation of newts on tadpoles, Cooke (1971)
demonstrated that tadpoles that had been exposed to DDT were less able to avoid
predation than controls. Further, because of the persistence of DDT and its metabo-
lites in the tadpoles, the predator was itself selecting a diet high in persistent neuro-
toxic compounds—an act of self-destruction. It has been argued that such selective
predation on prey highly contaminated by persistent neurotoxic pollutants may have
been quite widespread when these compounds were in regular use. Raptorial birds
such as the peregrine, for example, are attracted to prey that behaves abnormally;
for example, an individual bird fluttering on the ground can attract the attention of a
predator. Thus, when one considers the marked biomagnification of such compounds
that has occurred in food chains (see Chapter 2, Figure 2.8), selective predation may
have accentuated the problem of bioaccumulation.
Turning now to indirect effects of neurotoxic pollutants, the status of predators
and parasites can be affected by reductions in numbers of the species that they feed
upon. Thus, the reduction in numbers of a prey species due to a behavioral effect
can, if severe enough, cause a reduction in numbers of a predator. Also, as mentioned
earlier, behavioral effects upon a prey species may lead to selective bioaccumulation
of persistent neurotoxic pollutants such as DDT and dieldrin by predators; thus, a
behavioral effect may be hazardous for predator and prey alike!
When neurotoxic pollutants interact with their sites of action, consequent effects
on the functioning of the nervous system may be manifest in a variety of distur-
bances in behavior. Many of the latter have the potential to cause knock-on effects
at the level of population because of disruption of such activities as feeding, breed-
ing, and avoidance of predation. The question remains: to what extent were such
effects important in cases where population declines were attributed to neurotoxic
pollutants? In many instances, there is inadequate evidence to answer this question
retrospectively. Looking ahead, however, the development of biomarker strategies
and new biomarker assays could provide the technology for tackling future ecotoxi-
cological problems of this kind.
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