近日,，科學(xué)家們對美冠鸚鵡的線粒體基因組進行了測序,，發(fā)現(xiàn)這種產(chǎn)自澳洲的鳥類有著令人驚訝的進化史,。這項研究應(yīng)用了DNA測序和化石材料，發(fā)現(xiàn)那些擁有相似外形的鸚鵡未必有相近的親緣關(guān)系,，并對前人得到的美冠鸚鵡譜系提出了修改意見,。相關(guān)研究發(fā)表在《分子進化及系統(tǒng)發(fā)育》（Molecular Phylogenetics and Evolution）雜志上。
“我們的研究結(jié)果再次證明,，表型分類法未必準(zhǔn)確，分類的關(guān)鍵在DNA分子,，”研究的承擔(dān)者,，來自澳洲莫道克大學(xué)（Murdoch University）的N.White說。“之前還有研究將鳥類行為作為分類依據(jù),，這種方法和DNA方法是不可同日而語的,。”
美冠鸚鵡屬于鸚形目（Psittaciformes），這是一個高度分化的類群,，鸚形目分為三個科：啄羊鸚鵡科（Nestoridae）,、鳳頭鸚鵡科(Cacatuidae)和 鸚鵡科（Psittacidae），其中美冠鸚鵡屬于鳳頭鸚鵡科,。鸚形目內(nèi)部的分化情況過去是一個富有爭議的問題,，因為由分子生物學(xué)技術(shù)得到的譜系和化石記錄所得到的分化時間并不相同。
“在幾個關(guān)于鸚鵡類演化的研究中,，人們認(rèn)為啄羊鸚鵡從鸚形目主流中分開的時間,，和新西蘭島脫離澳大利亞的時間相同——都是在8200萬年前的白堊紀(jì)晚期,。”瑞士伯爾尼自然歷史博物館的鳥類學(xué)家M.Schweizer說。“該研究使用了化石記錄和可靠的分析技術(shù),，發(fā)現(xiàn)其實現(xiàn)代鸚鵡的分化時間很晚,，大約在始新世中晚期。”
White的研究小組使用了40種線粒體基因組（包括5種新測定的美冠鸚鵡基因組）和多種化石材料,，對前人推斷的鸚形目譜系進行了修改和校正,。她認(rèn)為，4千萬年前澳大利亞和南極大陸分開時,，美冠鸚鵡才從鸚形目主干中分離出來,。
研究小組著重考察了風(fēng)頭鸚鵡科內(nèi)部的分化，對前人的結(jié)論提出了挑戰(zhàn)：以前認(rèn)為,，產(chǎn)自昆士蘭約克角半島（Cape York Peninsula）的黑葵花鸚鵡（black palmcockatoo）是美冠鸚鵡類群的最早共同祖先,，但研究小組的結(jié)論推翻了這一看法。
“學(xué)界普遍認(rèn)為黑葵花鸚鵡是所有美冠鸚鵡的祖先,，但它其實是譜系上的一個側(cè)枝,。”她說。“另外,，羽毛顏色跟譜系也沒有關(guān)系,。”
中新世-上新世過渡時期，鸚鵡的多樣性顯著增加,。在那時,，澳洲雨林面積減小，取而代之的是開闊的草地,。氣候和生境的變化可能驅(qū)動了美冠鸚鵡的分化,。（生物谷Bioon.com）
生物谷推薦原文出處：
Molecular Phylogenetics and Evolution doi:10.1016/j.ympev.2011.03.011
The evolutionary history of cockatoos (Aves: Psittaciformes: Cacatuidae)
Nicole E. Whitea, , , Matthew J. Phillipsb, M. Thomas P. Gilbertc, Alonzo Alfaro-Nú?ezc, Eske Willerslevc, Peter R. Mawsond, Peter B.S. Spencera and Michael Buncea, ,
Abstract
Cockatoos are the distinctive family Cacatuidae, a major lineage of the order of parrots (Psittaciformes) and distributed throughout the Australasian region of the world. However, the evolutionary history of cockatoos is not well understood. We investigated the phylogeny of cockatoos based on three mitochondrial and three nuclear DNA genes obtained from 16 of 21 species of Cacatuidae. In addition, five novel mitochondrial genomes were used to estimate time of divergence and our estimates indicate Cacatuidae diverged from Psittacidae approximately 40.7 million years ago (95% CI 51.6–30.3 Ma) during the Eocene. Our data shows Cacatuidae began to diversify approximately 27.9 Ma (95% CI 38.1–18.3 Ma) during the Oligocene. The early to middle Miocene (20–10 Ma) was a significant period in the evolution of modern Australian environments and vegetation, in which a transformation from mainly mesic to xeric habitats (e.g., fire-adapted sclerophyll vegetation and grasslands) occurred. We hypothesize that this environmental transformation was a driving force behind the diversification of cockatoos. A detailed multi-locus molecular phylogeny enabled us to resolve the phylogenetic placements of the Palm Cockatoo (Probosciger aterrimus), Galah (Eolophus roseicapillus), Gang-gang Cockatoo (Callocephalon fimbriatum) and Cockatiel (Nymphicus hollandicus), which have historically been difficult to place within Cacatuidae. When the molecular evidence is analysed in concert with morphology, it is clear that many of the cockatoo species’ diagnostic phenotypic traits such as plumage colour, body size, wing shape and bill morphology have evolved in parallel or convergently across lineages.
