Failure of Theelin and Thyroxin to Affect Plumage and Eye-Color of the Blackbird. ∗

Abstract

Evidence from a number of sources has made it apparent that sexual differences in the plumage of the common fowl (Gallus) are largely regulated by endocrine factors. In most breeds feathers of the male type are replaced, after administration of appropriate amounts of thyroxin, theelin or crude pituitary extract, by feathers resembling those of the female. Nevertheless, it is recognized that there are pronounced differences between breeds in their response to these prepared hormones. 1 For a time it seemed possible that the mechanism of differentiation in secondary sexual characters might be essentially the same in all avian species, the variations being only quantitative in character. Evidence seeming to point in this direction was obtained from a number of different orders and families. 2 More recently evidence of another sort has been accumulating. Males of the variegated South American plover, Vanellus chilensis, 3 the pigeon and the guinea fowl, in all of which the sexes are similar, have shown no plumage response to the injection of theelin, nor in the latter species to castration. The plumage of the female guinea fowl is likewise unaffected by ovariectomy. 4 The extensive studies of Keck 5 on the English sparrow have shown that the distinctive plumages of the male and female of this species are not influenced by castration or by gonad transplantation.

These results indicate that the basis for the manifestation of sexual differences in plumage is not the same in all species. It apparently may differ radically within the same family (e. g., Fringillidae), 2 , 5 when genera and even species may show interesting deviations, 6 , 7 some of which suggest those found in breeds of poultry.