186
The Biology of Sea Turtles, Vol. II
These molecular stress responses have been studied mostly in organisms maintained under constant laboratory conditions; there is much less information on the
regulation of stress responses in animals that are exposed to and tolerate large
fluctuations in internal or external conditions (Rabergh et al., 2000). However,
genetic changes such as increased HSP expression are becoming an important and
powerful tool through which the direct effects of different stressors on organismal
health and fitness can be measured by their effects on cellular and molecular processes. Most attempts to monitor the environmental status of an ecosystem rely on
determining the abiotic components, such as contaminant analysis–loads, or assessing ecological responses to stressors (e.g., species richness, sex ratios, and indicator
species fitness) (O’Connor, 1996). Such studies do not reveal the links between the
stressor and its effects, and therefore we cannot predict how a species or ecosystem
will respond to even one contaminant (Downs et al., 2001a), much less the more
likely problem of a suite of stressors.
A number of different compensatory mechanisms may operate at multiple levels
(cells, tissues, organ systems, and individual animal) to ameliorate stress before the
fitness of an individual or its functional role in the community is altered (Allen and
Starr, 1982), and thus stress affects higher levels of the biological hierarchy only
when it overwhelms the homeostatic mechanisms of individual organisms. Rather
than simply measuring stress responses, data regarding individual and population
responses (especially for endangered species) would be far more useful if they could
be used to forecast population changes. Forecasting stress responses in time to
intervene and prevent population declines, however, requires linking changes at
lower levels of biological organization with the fitness of individuals (and then
accurately modeling the long-term demographic consequences).
The use of molecular biomarkers to assess organismal and ecosystem health is
thus becoming a popular concept (Downs et al., 2001a). Although numerous studies,
including many on sea turtles, examine a single or small set of physiological parameters to assess the overall physiological response to a stressor (Adams et al., 1992),
and other studies support the validity of biomarker use as indicators of contaminant
or stressor exposure (de Zwart et al., 1999; Adams and Ryon, 1994), very few attempt
to integrate physiological status with multiple, specific biomarkers (Adams et al.,
1992; Stegmann et al., 1992). A system to simultaneously assess multiple biomarkers
to quantify known physiological responses to stressors would tell us: (1) whether
an animal is physiologically stressed, (2) whether the animal is evolutionarily or
physiologically adapted to a chronic stress, and (3) the physiological impact of the
stress (Downs et al., 2001a). Such an integrated system using molecular biomarkers
will allow for a diagnosis of an animal’s physiological condition at the cellular level
when challenged with a real or suspected stress.
With the development of molecular markers for specific individual or suites of
stressors, such a system would become a powerful tool to identify environmental
insults that are physiologically affecting an organism, providing a more accurate
quantification of the health status of a population in response to a natural or anthropogenic stressor. Such a system, for example, has been developed for the intertidal
eastern mud snail (Ilyanassa obsoleta), where biomarkers can differentiate between
snails exposed to different stressors, including heat, cadmium, an herbicide and a
1123 book.book Page 186 Monday, November 11, 2002 11:11 AM
The Biology of Sea Turtles, Vol. II
These molecular stress responses have been studied mostly in organisms maintained under constant laboratory conditions; there is much less information on the
regulation of stress responses in animals that are exposed to and tolerate large
fluctuations in internal or external conditions (Rabergh et al., 2000). However,
genetic changes such as increased HSP expression are becoming an important and
powerful tool through which the direct effects of different stressors on organismal
health and fitness can be measured by their effects on cellular and molecular processes. Most attempts to monitor the environmental status of an ecosystem rely on
determining the abiotic components, such as contaminant analysis–loads, or assessing ecological responses to stressors (e.g., species richness, sex ratios, and indicator
species fitness) (O’Connor, 1996). Such studies do not reveal the links between the
stressor and its effects, and therefore we cannot predict how a species or ecosystem
will respond to even one contaminant (Downs et al., 2001a), much less the more
likely problem of a suite of stressors.
A number of different compensatory mechanisms may operate at multiple levels
(cells, tissues, organ systems, and individual animal) to ameliorate stress before the
fitness of an individual or its functional role in the community is altered (Allen and
Starr, 1982), and thus stress affects higher levels of the biological hierarchy only
when it overwhelms the homeostatic mechanisms of individual organisms. Rather
than simply measuring stress responses, data regarding individual and population
responses (especially for endangered species) would be far more useful if they could
be used to forecast population changes. Forecasting stress responses in time to
intervene and prevent population declines, however, requires linking changes at
lower levels of biological organization with the fitness of individuals (and then
accurately modeling the long-term demographic consequences).
The use of molecular biomarkers to assess organismal and ecosystem health is
thus becoming a popular concept (Downs et al., 2001a). Although numerous studies,
including many on sea turtles, examine a single or small set of physiological parameters to assess the overall physiological response to a stressor (Adams et al., 1992),
and other studies support the validity of biomarker use as indicators of contaminant
or stressor exposure (de Zwart et al., 1999; Adams and Ryon, 1994), very few attempt
to integrate physiological status with multiple, specific biomarkers (Adams et al.,
1992; Stegmann et al., 1992). A system to simultaneously assess multiple biomarkers
to quantify known physiological responses to stressors would tell us: (1) whether
an animal is physiologically stressed, (2) whether the animal is evolutionarily or
physiologically adapted to a chronic stress, and (3) the physiological impact of the
stress (Downs et al., 2001a). Such an integrated system using molecular biomarkers
will allow for a diagnosis of an animal’s physiological condition at the cellular level
when challenged with a real or suspected stress.
With the development of molecular markers for specific individual or suites of
stressors, such a system would become a powerful tool to identify environmental
insults that are physiologically affecting an organism, providing a more accurate
quantification of the health status of a population in response to a natural or anthropogenic stressor. Such a system, for example, has been developed for the intertidal
eastern mud snail (Ilyanassa obsoleta), where biomarkers can differentiate between
snails exposed to different stressors, including heat, cadmium, an herbicide and a
1123 book.book Page 186 Monday, November 11, 2002 11:11 AM