1354 



HORMONAL REGULATION OF BEHAVIOR 



skin is not sensitive to the hormones which 

 induce it in other species. 



It is apparent that, both in birds and in 

 mammals, a variety of hormonal mecha- 

 nisms, and of types of tissue responsiveness 

 to hormones, may be found in different spe- 

 cies, and that, as a consequence, similar be- 

 havior patterns in different animals may 

 sometimes be underlain by rather different 

 physiologic mechanisms. 



2. Strain Differences and Genetic Factors 



Although the study of behavior genetics 

 has been growing very rapidly in recent 

 years (Fuller, 1960; Fuller and Thompson, 

 1960), little information is available about 

 genetic factors influencing parental behav- 

 ior. It is to be hoped that this deficiency will 

 soon be remedied. 



Different strains of domestic hens differ 

 sharply with respect to the number of birds 

 which become "broody," thus interrupting 

 their egg production (Pearl, 1914). For ex- 

 ample, Goodale (1916) noted that only 

 2 to 3 per cent of White Leghorn hens ever 

 become broody, compared with 93 per cent 

 of Rhode Island Red hens. Riddle, Bates 

 and Lahr (1935) found that prolactin in- 

 jected into laying hens induced incubation 

 behavior in 16 out of 20 birds of a broody 

 race, but in only 1 out of 10 birds of a non- 

 broody race. Similarly, Nalbandov and Card 

 (1945) found that the amount of prolactin 

 required to induce roosters to care for 

 chicks was much greater when the birds 

 came from a nonbroody race than when 

 they were of a broody race. For example, 

 White Leghorn roosters required 500 to 

 700 I.U. of prolactin, whereas Cornish 

 roosters required only 300. (Note that 50 

 I.U. is sufficient to induce broodiness in a 

 laying heji.) Bates, Riddle, and Lahr (1939) 

 found that different races and strains of 

 pigeons differ markedly in their response to 

 prolactin. Some strains required as much as 

 5 to 8 times as much prolactin as did others, 

 for the same effect on the crop-sac. Byerly 

 and Burrows (1936) found that the pitui- 

 tary glands of genetically broody hens con- 

 tained more prolactin than did those of 

 nonbroody birds. This suggests that the 

 broody and nonbroody races may differ not 

 only in their responsiveness to prolactin, but 

 also in their production of this hormone. 



Carson, Bacon, Beall and Ryan (1960) 

 found that broodiness interferes with egg 

 production in some strains of fowl, but not 

 in others. 



Goodale, Sanborn and White (1920) 

 showed that a nonbroody strain could be 

 quickly developed from a broody one by 

 selective breeding. Yamashina (1956a, b) 

 selected nonbroody females from among a 

 flock of Plymouth Rocks, and mated them 

 with males which could not be made broody 

 by prolactin injection. By this method, he 

 reduced the percentage of broodiness in the 

 flock from 84.5 per cent to 3.8 per cent. 

 Various investigators have shown that 

 broodiness depends on several pairs of genes, 

 some sex-linked, some autosomal (Punnett 

 and Bailey, 1920; Roberts and Card, 1934; 

 Hays, 1940; Kaufman, 1948). 



Leopold (1944) compared the behavior of 

 wild turkeys with that of domesticated and 

 hybrid strains. Wild mother birds with 

 young tended to crouch quietly at the ap- 

 proach of a human, whereas the domestic 

 and hybrid mothers noisily led their young 

 away. Leopold related the differences in 

 wildness between the two strains of turkeys 

 in ])art to differences in adrenal physiology, 

 the ratio of adrenal weight to body weight 

 being more than twice as great in the wild 

 birds as in the domestic strain. 



Sawin and Curran (1952) found that 

 various strains of rabbits, developed in their 

 laboratory, differed with respect to the 

 time of nest-building, the average quality 

 of the nest, the choice of location of the 

 nest, and the extent to which young were 

 scattered, or in some cases eaten. The 

 strains which they studied had been pro- 

 duced by selection for studies of growth and 

 differentiation, not for breeding character- 

 istics. As we might expect, they found no 

 evidence of a single factor for "maternal 

 behavior," since various of the characters 

 with respect to which they found race dif- 

 ferences were correlated with each other in 

 some races, and not in others. In a later 

 study, Sawin and Crary (1953) suggested 

 at least two or three genetic factors, one 

 influencing the time of building and lining 

 the nest, others determining the nature of 

 the nest, the quantity of the lining, etc. 

 Hauschka (1952), studying strains of mice 



