Living and Adapting to Its Own Habitat - Building the Most Complex Structure on Earth - page 196

different changes in its morphology, morphometry, behavior, and life history, when
it perceives each of its predators, the water bugs and crayfishes ( Hoverman et al.,
2005 ). When the pregnant viviparous lizard Pseudemoia pagenstecheri olfactorily
perceives the presence of predator snakes, it gives birth to bigger bodied offspring
with longer tails, thus improving their survival chance ( Shine and Downes, 1999 ).
Several polar predator and prey mammals (and even birds) in the winter months turn
their color into white to adapt to the snow-covered landscape. For interested readers,
there is ample evidence in the scientific literature on the intragenerational and TDP.
A behavioral adaptation is observed in some species of the crustacean Daphnia
(Cladocera) that respond to the rising water temperature by swimming up (upward)
and sinking deeper when the water temperature drops ( Gerritsen, 1982 ).
Finally, certain tadpoles display an adaptive change in their life history in
response to environmental stimuli. Tadpoles of the western toad ( Bufo boreas )
respond adaptively upon detecting chemical cues of their predators, aquatic insect
backswimmers of Notonecta species in their environment; they accelerate their
growth and development to reach the metamorphosis stage earlier, thus reducing
their exposure to predators ( Chivers et al., 1999 ).
Most stimuli act as stressors. Although adaptive responses to particular stimuli
are generally specific, they are commonly associated with a general and nonspecific
stress response, which evolved as an adaptive mechanism. The stress response is a
systemic general response regardless of the stressors that trigger it. It involves physi-
ological, psychological, life history, and rarely even morphological changes. The
CNS is the central venue of the stress response. Acute stress activates the locus coer-
uleus and the brain stem, which stimulate the sympathetic-adrenomedullary system,
with resulting “fight or flight” behavior intended for the survival of the individual. It
is associated with a number of physiological and behavioral changes.
Homeostatic mechanisms are strained and homeostasis may be disturbed, under
the action of stressors. The disturbed homeostasis is assessed in the brain and the
adaptive stress response starts in the higher brain centers. In vertebrates, the stress
condition may also be triggered before stressors affect homeostasis. It may be trig-
gered as a direct response to the perception of threatening situations, while in higher
vertebrates, especially in humans, stress conditions may be caused not only by real,
but even by imagined stressors.
The stress response may be immediate or delayed. The immediate stress response
results from the perception of a threat or a threatening condition.
Neural Control of Gene Expression
Since 1930s, the genecentric view has dominated theoretical biology. The enthu-
siasm generated by the landmark discoveries in molecular genetics silenced dis-
senting biologists. However, the expected crowning of the genecentric age, the era
of genome sequencing failed to impress; essentially the same genes and the same
“genetic toolkit” were used across metazoan taxa, from primitive worms to insects
and vertebrates.