Improving the Adaptability of Animals by Selection - Genetics and the Behavior of Domestic Animals - page 297

placed in a novel environment. Reduced activity is due to increased fear
levels and leads to increased freezing and the suppression of general activity.
In both the SR and TI lines, responses to selection were asymmetrical
( Figures 8.2 and 8.6 ). These asymmetrical responses are likely to have been
due to an artificial ceiling or actual floor limits to selection. For example, the
duration of TI cannot be less than 0 (a reduction of 100% relative to the first
generation (F0), whereas the upper limit of TI was 300 seconds (an increase
of approximately 600% relative to the F0 score).

STABILITY OF THE SELECTION RESULTS
One problem with selection for a specific trait at a certain age is that the
response to selection may be specific to the age at which the measure was
made. We therefore verified that behavioral differences observed at 6

10 days
of age were also present in older animals. Quail were tested for tonic immobility
and distance run on the treadmill using the same methods employed for selec-
tion of breeding animals. However, the maximum duration of TI measurements
were lengthened to 30 minutes. Different animals were tested at 1, 2, 4, 6, or
10 weeks of age Launay et al., 1993 ; Launay, 1993 ).
The duration of tonic mobility varied with age ( Figure 8.10 ). However, the
scores of the long TI and short TI lines differed significantly at all ages.
Comparison of Figure 8.10a and Figure 8.6 shows that the maximum duration
of tonic immobility in the long TI line was underestimated because TI testing
was terminated after only 5 minutes. Data shown in Figure 8.10 are for quail
from the 13th generation of selection; the mean duration of tonic immobility in
the long TI line at 1 week of age was over 400 seconds whereas the truncated
values obtained in the selection program were less than 200 seconds.
Distance run on the treadmill was also age dependent ( Figure 8.10b ).
However, the differences between the high SR and low SR lines were signifi-
cant at all ages tested. Since differences in the characteristics selected persisted
into adulthood, it seems likely that genetic selection has modified the behavior
of the birds throughout their lives rather than only at a specific age.

FEAR REACTIONS
Ratner (1967) proposed that fear (antipredator) reactions may be dependent
on the proximity to the predator. When the predator is distant, the animal's
first reaction is freezing. Freezing behavior may serve to reduce the likeli-
hood of detection. When the predator approaches, flight is the prevalent reac-
tion. If the bird is not able to escape from the predator, it shows fight
responses. If this fails, tonic immobility follows. The open-field test provides
a means for treating this hypothesis.
The open-field test is commonly used as a means of measuring fear in
birds and mammals ( Hall, 1934 ). The open-field test involves the introduction