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The evolution of plumage colors in Corvidae

The evolution of plumage colors in Corvidae
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대학원 에코과학부
이화여자대학교 대학원
Melanin is the most abundant and widespread pigment in animal kingdom. It can create a wide array of colors including brown, matt black and iridescent black. The color that is produced depends on the structure and arrangement in the melanin granules in the color producing organs. In this study, I investigated genetic and structural bases for the variation in plumage colors in a series of species that belong to the family Corvidae. Specifically, I aimed to correlate the genetic difference in a marker that is known to be involved in the production of melanin (melanocortin 1 receptor, MC1R), difference in the distribution and arrangement of melanin granules, and the difference in the color that is produced by the structural components. Plumage parts of Eurasian jays (Garrulus glandarius), Mexican jays (Apehlocoma ultramarina), Azure-winged magpies (Cyanopica cyana), Black-billed magpies (Pica pica), Large-billed crows (Corvus macrorhynchos), Daurian Jackdaw (Corvus dauuricus) and Spotted Nutcracker (Nucifraga caryocatactes) were used in this study. Transmission electron microscopic images on the cross-section of feather barbules were used to describe the distribution and the shape of melanin granules in the plumage parts that show common (i.e. black) and species-specific colors (i.e. brown, blue or iridescent). Three coloration schemes were found in Corvidae. Matte colors of black and brown were produced both from barbs and barbules. Non-iridescent structural colors were mainly produced from barbs. Iridescent structural colors were produced from distal barbules only. In general, the shape and arrangement of melanin granules were similar within a species. However, this seems to be confined to those species that show uniform color across the body parts. Evolution of iridescence in Corvidae seems to be correlated with the increase in density of melanin granules and the formation of densely packed layer of melanin granules. Shape and arrangement of melanin granules in black-billed magpie feathers were distinct from others. Melanin granules of black-billed magpies were small and air-filled, and they form 2-5 layers, which would result in the strong iridescent color. In Corvidae, variation in the shape and arrangements of melanin granules was not congruent with the pattern of MC1R sequence divergence. It may be related to the fact that, in Corvidae, melanin-based coloration is an ancestral trait and the evolutionary switch between phaeomelanin-dominant coloration and eumelanin-dominant coloration is rare.;멜라닌은 동물에게서 가장 흔히 볼 수 있는 색소이다. 조류에서도 멜라닌은 다양한 기능을 하며 물리적인 충격으로부터의 보호, 기생충으로부터의 보호, 위장과 신호로서의 역할을 한다. 멜라노솜의 구조와 배열의 차이에 의해 갈색, 윤기없는 검은색, 무지개빛의 구조색 등의 색을 가진 깃털이 만들어진다. 이 연구에서는 까마귀과인 어치, 멕시칸제이, 물까치, 큰부리까마귀, 갈까마귀, 잣까마귀, 떼까마귀, 까치를 대상으로 실험을 진행하였다. 이들 종에서 검은색, 갈색, 파란색, 흰색, 무지개빛 깃털을 사용하였다. 투과전자현미경(TEM)을 이용하여 이들 종의 distal barbule 단면에 있는 멜라노솜의 구조와 배열을 관찰하였다. 또한 멜라닌을 만드는데 관여하는 유전자라고 알려진 MC1R 유전자의 종별 차이도 분석하였다. 그 결과 검은색과 갈색의 깃털은 barb와 barbule이 동일한 색을 가지고 있었으며, 무지개빛이 아닌 구조색의 깃털은 barb에서 파란색 혹은 흰색이 나타나고 있었다. 마지막으로 무지개빛인 구조색 깃털은 distal barbule에서 무지개빛이 나타났다. 일반적으로 멜라노솜의 모양과 배열의 차이는 종보다는 깃털의 색과 많은 관련이 있었다. 그러나 같은 색의 깃털일지라 하더라도 멜라노솜의 모양과 배열이 완전히 일치하는 것은 아니었다. 까치는 다른 종들과는 구별되는 매우 독특한 멜라노솜 구조와 배열을 가지고 있었으며 멜라닌의 분포와 배열, 형태의 종별 차이는 MC1R 유전자의 종별 차이와 일치하지 않았다.
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