Improving the Adaptability of Animals by Selection - Genetics and the Behavior of Domestic Animals - page 309

(a) 4 1.25

(b)

1

3

0.75

2

0.5

1

0.25

0 0

LTI CTI STI LTI CTI STI

FIGURE 8.22 Meat water loss (a) and 24-hour post mortem pH decrease (b) following 15 min-
utes in a crush cage in lines of quail selected for long or short duration of tonic immobility and
for high or low levels of social reinstatement behavior over 18 generations. ( ' ) Stressed,

( & ) control.

neurotransmitter receptors in the forebrains of long TI (high fear) and short
TI (low fear) birds in an attempt to determine neuroanatomical and biochem-
ical differences between lines.
Neurotransmitters are “messenger” substances secreted by nerve endings
which cross the synapses (the junctions between nerve endings) and bind to
their specific receptor sites on adjoining nerve endings. For example, seroto-
nin transmitters bind to serotonin receptors like a key fitting in a lock. The
brain contains many different neurotransmitters and corresponding receptor
sites. These transmitters have a wide variety of influences on behavior rang-
ing from calming to excitatory effects. Behavioral effects can be affected by
both the number of receptor sites for a certain transmitter and the affinity of
the receptor sites. To explain it very simply, a greater number of receptors or
an increase in the affinity of binding at each site will influence the “strength”
of transmission. Documentation of a relationship between genetic selection
for traits, such as high or low levels of fear and the number and affinity of
different receptor sites, indicates that genetic selection affects brain mechan-
isms which influence behavior.
One of the brain areas involved in fear reactions in birds is the archistria-
tum (Davies et al., 1996); the effects of lesions of this area have been studied
( Davies et al., 1997; Grignard, 1996 ). In young animals, archistriatal lesions
have limited effects in the short TI, high SR, and low SR lines. However,
such lesions decrease fear reactions in the highly fearful long TI chicks as
measured by decreased latency to peep, increased number of peeps in
the hole in the wall box test, and a decreased duration of TI ( Davies et al.,
1997 ). Lesioned sub-adult long TI line quail were easier to capture and
had reduced avoidance of novel objects, people, and unfamiliar

food