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Testosterone and Daylength-Dependent Development of Comb Size and Breeding Plumage of Male Willow Ptarmigan (Lagopus lagopus lagopus)
Vol. 96, No. 1 (Jan., 1979), pp. 106-115
Published by: American Ornithologists' Union
Stable URL: http://www.jstor.org/stable/4085405
Page Count: 10
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Photostimulation of male Willow Ptarmigan resulted in a rapid molt from the white winter plumage to the pigmented plumage of the breeding bird. In castrated ptarmigan the breeding plumage was omitted, resulting in a slow molt from white to pigmented summer (post-nuptial) plumage. Feathers were plucked from the head and back of castrated and intact birds kept on short daylength to investigate the effects of testosterone on feather pigmentation. Both castration and testosterone treatment resulted in pigmentation of regenerating feathers, while the untreated, intact birds regenerated white feathers. Pigmented feathers that regenerated on short daylengths in castrated or testosterone-treated birds were similar to each other, but were not the same as any type of pigmented feather seen in intact or castrated birds exposed to long daylengths. Pigmented feathers that generated in testosterone-treated intact or castrated birds on long daylengths were the same as feathers in breeding males. When compared with control birds, testosterone treatment shortened the interval between photostimulation and the beginning of the molt, while castration markedly lengthened this interval. Together with the photostimulated development of pigmented breeding plumage in intact males, there was a 100% increase of comb height. Castrates did not show any comb growth, whereas testosterone treatment always resulted in a rapid comb growth, both in intact males on short daylengths and in castrates on short daylengths and on long daylengths. In the male Willow Ptarmigan, testosterone and perhaps gonadotrophins (LH) affect the pigment producing system. There is a daylength dependent testosterone induction of molt from winter to breeding plumage, and a testosterone-stimulated and a testosterone-dependent comb growth.
The Auk © 1979 American Ornithologists' Union