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LT I
CTI
STI
FIGURE 8.21
Plasma corticosterone levels after 15 minutes in a crush cage, in lines of quails
selected for long or short duration of tonic immobility and for high or low level of social rein-
statement behavior over 18 generations. (
'
) Stressed, (
&
) control.
because tonic immobility and freezing were likely to be induced by the
highly stressful nature of the crush cage test. The only explanation we can
suggest for this is that the TI reaction not only protects and animal from pre-
dators, but also allows the animal to cut itself off from noxious or frightening
stimuli. It appears that the struggling and fighting displayed by the low TI
birds was a more stressful response (as measured by stress more levels in the
blood), compared to the freezing response expressed in high TI birds. Each
have adaptive significance Freezing behavior protects birds from being
detected by the predator, fighting and struggling may also protect the bird
once the predator has caught it.
Stress reduces meat quality by increasing water loss and decreasing pH
(
Remingnon et al., 1996
). When water loss and pH decrease 24 hours post
mortem were measured in the muscle from three lines (short TI, control, and
long TI), control values for these two measures were identical. However,
following stress muscle from long TI birds showed a higher percentage of
water loss and a lower pH decrease than did tissue in their unstressed coun-
terparts, from stressed or unstressed controls, and from the short TI line
(
Figure 8.22
). In quail raised for meat, long TI birds may have reduced meat
quality because they may be more likely to be stressed by handling and
transport prior to slaughter.
NEUROBIOLOGY
Little is known about the effects of genetic selection on brain function.
Selection for behavioral characteristics should theoretically result in neuro-
physiological traits. We have studied the number and binding activity of
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