The puppies used in the experiments lived with their litter-mates from birth until 1 yr. of age, first in large nursery rooms and later in spacious outdoor runs. Behavioural tests were given to animals of 5 different breeds: Basenji, Beagle, Cocker Spaniel, Shetland Sheep Dog, and Wire-haired Fox Terrier. Reciprocal crosses were made between the 2 breeds that differed in the greatest number of respects: Cocker Spaniel and Basenji. F1 [male][male] were backcrossed to their dams and also mated with their sisters. Crosses were subjected to the same tests as their purebred ancestors.
The standard stimulus situation in which barking could be measured was one in which pairs of puppies were allowed to compete for a bone for a 10 min. period at 5, 11 and 15 wks. of age. Barking did not occur in the neonatal period in any breed. At 5 wks. of age, before the development of a dominance order, there was little barking. At 11 wks. of age, when dominance relationships were unstable, barking rose to a peak. It declined again at 15 wks., when the dominance order had become more stable. Since max. breed differences appeared at 11 wks., this age was chosen for detailed genetic analysis.
Cockers and Basenjis differed in 3 ways: the quality of the bark, the threshold of stimulation, and the tendency to continue barking when aroused. Most Basenjis and all Cockers barked at some time or other, but not all barked in the test situation. Basenjis seemed to bark only under very strong stimulation. In the dominance test at 11 wks. the threshold was reached for about 95% of Cockers and 40% of Basenjis. An even greater breed difference was obtained by comparing the number of animals barking per opportunity (68% in Cockers and 20% in Basenjis). Basenjis usually stopped barking after 2 or 3 barks, whereas Cockers barked repeatedly; 95% of Basenjis and only 18% of Cockers gave fewer than 19 barks once the threshold was crossed.
In crosses between Basenjis and Cockers the threshold of response was very close to that of the Cocker parent. A single dominant factor appears to be involved in the inheritance of this trait. In amount of barking the F1 crosses were intermediate, as were the F2. Backcrosses to either pure breed fell between the F1 and the purebred parent, suggesting that there is no dominance in respect of this trait. The data here are partially consistent with the action of a single major gene modified by environmental factors or other genie systems. The Basenji showed little variability in amount of barking, while the Cocker was highly variable, and the F1 and F2 were moderately variable. The backcross to the Basenji was less variable than the backcross to the Cocker. It is suggested that what is inherited is not the capacity to develop a particular amount of barking but the capacity to be variable in behaviour.
|Publication Title||American Zoologist|
|Author Address||Jackson Lab., Bar Harbor, Me.|
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