類胡蘿蔔素呈色及黑色素呈色的特徵在紅嘴黑鵯的研究
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2015
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鳥類體表顏色多樣性極大，這些顏色大部分具有功能性，對於鳥類溝通非常重要。在各種體表顏色中，由類胡蘿蔔素呈色 (呈現黃、橘或紅色)以及黑色素呈色（黑、灰或棕色）的特徵是最普遍也最重要的特徵。這類特徵通常能傳遞個體的訊息，並且具有重要的功能，例如個體可據此選擇配偶或評估對手。傳統上，類胡蘿蔔素呈色的特徵，被普遍認為是個體選擇配偶的依據，而黑色素呈色的特徵，則被認為與社會互動有關。但是這種觀念已被質疑，因為隨著越來越多的鳥種被研究，發現這兩種特徵在不同種類，可能功能不同，顯示這兩種特徵在鳥類的演化機制，可能比目前所知的更為複雜。除此之外，大部分的相關研究都在探討這兩類特徵在性擇上扮演的角色，所以多是以兩性有明顯型態差異的物種為研究標的（這類物種通常可能受到較高的性擇壓力），較少以在兩性型態差異較小的物種為主題，而這些物種可能受到與兩性型態差異大的物種不同的選汰壓力。為了能更完整地了解顏色在鳥類溝通上的演化機制，需要研究這兩類特徵在兩性型態差異較小的物種上扮演的角色。本研究選擇紅嘴黑鵯 (Hypsipetes leucocephalus nigerrimus )為研究物種,他們具有類胡蘿蔔素呈色的喙部、跗蹠與黑色素呈色的羽毛，對人眼來說是雌雄單型性的鳥種。我的結果顯示，在鳥類視覺上，這兩類特徵在兩性間是有差異的。而類胡蘿蔔素呈色的喙部與黑色素呈色的胸部與肩部羽毛的顏色表現，也與個體的生理狀況（包括個體的免疫能力與受到的氧化壓力）有關。雌性偏好試驗的結果顯示，單獨類胡蘿蔔素呈色的部位，可能不是雌性黑鵯選擇配偶的依據。我的論文提出清楚的證據，顯示類胡蘿蔔素呈色以及黑色素呈色的特徵，都能顯示紅嘴黑鵯個體的生理狀況，因此對紅嘴黑鵯而言，這些特徵可能具有重要的功能。但是要知道這些特徵在這個物種真正的功能，還需要之後更詳細的研究。
Integumentary colorations are essential signals in avian communication. Among all the various color types, carotenoid-based (expressed in yellow, orange or red) and melanin-based (expressed in black, grey or brown) colors are the most common and important traits in birds. Studies have shown that these traits are informative and serve vital functions, such as cues for choosing mates or assessing opponents. Traditionally, in avian communication, carotenoid-based colors are thought to be sexually selected traits and melanin-based colors signal social status. However, the results of various studies indicate these traits serve several functions in different avian species. It suggests that the evolution of both traits is more complex than we used to think. Nevertheless, most relevant studies have focused on the role in sexual dichromatic species, which might be suggested to be under higher pressure of sexual selection. There is a gap of how these traits evolved and what their functions are in less sexually dichromatic species, which might be under different selection regimes from sexually dichromatic ones. In order to understand the imperatives of coloration in avian communication completely, studies to characterize variations and functionality of both traits on less sexually dichromatic species are needed. I chose to study Himalayan black bulbuls (Hypsipetes leucocephalus nigerrimus), which are sexually monomorphic to human vision and contain a carotenoid-based bill and tarsi and melanin-based plumage to analyze the possible roles of both types of traits. My results showed that both carotenoid- and several melanin-based parts were sexually dichromatic in avian vision. Furthermore, I found that the expression of a carotenoid-based bill and melanin-based breast and scapular colorations were correlated with individuals’ physical conditions, including immunocompetence and oxidative stress levels. The results of the female-preference test on carotenoid-based traits showed that the red bared parts alone may not be the cues for mate choice for female black bulbuls. My dissertation provides clear evidence that both carotenoid- and melanin-based traits should be informative cues reflecting bearers’ physical condition; it suggests that these traits may play a role in the signaling of Himalayan black bulbuls, but the functions of the traits need to be further investigated.
Integumentary colorations are essential signals in avian communication. Among all the various color types, carotenoid-based (expressed in yellow, orange or red) and melanin-based (expressed in black, grey or brown) colors are the most common and important traits in birds. Studies have shown that these traits are informative and serve vital functions, such as cues for choosing mates or assessing opponents. Traditionally, in avian communication, carotenoid-based colors are thought to be sexually selected traits and melanin-based colors signal social status. However, the results of various studies indicate these traits serve several functions in different avian species. It suggests that the evolution of both traits is more complex than we used to think. Nevertheless, most relevant studies have focused on the role in sexual dichromatic species, which might be suggested to be under higher pressure of sexual selection. There is a gap of how these traits evolved and what their functions are in less sexually dichromatic species, which might be under different selection regimes from sexually dichromatic ones. In order to understand the imperatives of coloration in avian communication completely, studies to characterize variations and functionality of both traits on less sexually dichromatic species are needed. I chose to study Himalayan black bulbuls (Hypsipetes leucocephalus nigerrimus), which are sexually monomorphic to human vision and contain a carotenoid-based bill and tarsi and melanin-based plumage to analyze the possible roles of both types of traits. My results showed that both carotenoid- and several melanin-based parts were sexually dichromatic in avian vision. Furthermore, I found that the expression of a carotenoid-based bill and melanin-based breast and scapular colorations were correlated with individuals’ physical conditions, including immunocompetence and oxidative stress levels. The results of the female-preference test on carotenoid-based traits showed that the red bared parts alone may not be the cues for mate choice for female black bulbuls. My dissertation provides clear evidence that both carotenoid- and melanin-based traits should be informative cues reflecting bearers’ physical condition; it suggests that these traits may play a role in the signaling of Himalayan black bulbuls, but the functions of the traits need to be further investigated.
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紅嘴黑鵯, 類胡蘿蔔素, 黑色素, 性擇, 鳥類通訊, Himalayan black bulbul, Hypsipetes leucocephalus regerrimus, carotenoid-based trait, melanin-based trait, sexual selection, quality cue