科學(xué)家研究發(fā)現(xiàn)母鴨已經(jīng)進(jìn)化出一種避免因遭受具有螺絲錐形狀大陰莖而且頗有侵略性的公鴨強(qiáng)行性交而受孕的奇妙方式：那就是母鴨具有順時針螺旋的陰道,，這樣就能阻礙具有反向螺旋的雄性生殖器的進(jìn)入,。
關(guān)于這種在外生殖器方面發(fā)生的性別進(jìn)化之戰(zhàn)的詳細(xì)內(nèi)容發(fā)表在《皇家學(xué)會學(xué)報 B》(Proceedings of the Royal Society B) 雜志的第 12 月 23 日號刊物上,。
“在強(qiáng)迫性交司空見慣的物種內(nèi),，雄性通常已經(jīng)進(jìn)化出較長的陰莖,，但是雌性則共同進(jìn)化出具有和雄性陰莖相反的回旋方向而且一端不通的回旋狀陰道,，”該論文的主要作者兼生態(tài)學(xué)和進(jìn)化生物學(xué)系的博士后研究員 Patricia L.R. Brennan 說,。“這種共同進(jìn)化是在兩性的沖突之間由控制受精的一方所產(chǎn)生的,。”
這項(xiàng)研究是以 2007 年耶魯大學(xué)首次描述了鴨子性器官奇異生物形態(tài)的一份報告為基礎(chǔ)的,。盡管大多數(shù)鳥類并沒有陰莖，但是鴨子卻具有相對較大而可以彎曲的陰莖 – 它可長達(dá) 20 厘米并縮攏在公鴨體內(nèi),。性交時,，公鴨會在母鴨體內(nèi)伸展或翻轉(zhuǎn)其陰莖。耶魯大學(xué)的 Brennan 及其同事們首次利用高速攝像技術(shù)展示了鴨子陰莖的爆發(fā)式勃起,，整個過程僅耗時半秒鐘 – 這被耶魯?shù)难芯啃〗M稱之為“爆炸式性交”,。
在有很多強(qiáng)迫交配的情況下，這樣大的陰莖對于雄性而言本應(yīng)當(dāng)是有利于生殖的。不過,，耶魯?shù)难芯啃〗M假設(shè)雌鴨可能會憑借其復(fù)雜的外生殖器而使雄性的性交變得困難,。但某些水禽具有重疊螺旋的陰道是否能有助于雌鳥排斥強(qiáng)迫性交呢"
為了證實(shí)這一假設(shè)，Brennan 及其同事們檢查了鴨子的陰莖在一組具有不同形狀玻璃管內(nèi)的翻轉(zhuǎn)情況,。筆直的玻璃管,，或者和雄鴨的陰莖具有相同逆時針方向旋轉(zhuǎn)的玻璃管都沒有減慢陰莖勃起的過程。但是,，模擬雌性陰道順時針螺旋或突然彎曲的玻璃管則完全阻止了陰莖的翻轉(zhuǎn),。這些資料表明雌鴨已經(jīng)進(jìn)化出阻礙強(qiáng)迫性交的解剖學(xué)機(jī)制，同時也為在繁殖方面性別沖突的進(jìn)化結(jié)果提供了全新的見解,。
為了控制繁殖而在解剖學(xué)方面發(fā)生的進(jìn)化競賽無疑是自然界性別沖突更為戲劇性的例證之一,。
“盡管我們預(yù)先知道性別沖突是普遍存在的，而要發(fā)現(xiàn)兩性之間具有如此戲劇性“軍備競賽”的體系則真是非常難得的,。鴨子為我們提供了理解性別沖突進(jìn)化結(jié)果的難以置信的機(jī)會,，”Brennan 表示。（生物谷Bioon.com）
相關(guān)閱讀：
PNAS：人造兔子陰莖制作成功
Hum. Reprod. ：用干細(xì)胞制造女性生殖器
生物谷推薦原始出處：
Proceedings of the Royal Society B December 23, 2009, doi: 10.1098/rspb.2009.2139
Explosive eversion and functional morphology of the duck penis supports sexual conflict in waterfowl genitalia
Patricia L. R. Brennan1,2,*, Christopher J. Clark1,2 and Richard O. Prum1,2
1Department of Ecology and Evolutionary Biology, Yale University, New Haven, CT 06511, USA
2The Peabody Museum of Natural History, Yale University, New Haven, CT 06511, USA
Coevolution of male and female genitalia in waterfowl has been hypothesized to occur through sexual conflict. This hypothesis raises questions about the functional morphology of the waterfowl penis and the mechanics of copulation in waterfowl, which are poorly understood. We used high-speed video of phallus eversion and histology to describe for the first time the functional morphology of the avian penis. Eversion of the 20 cm muscovy duck penis is explosive, taking an average of 0.36 s, and achieving a maximum velocity of 1.6 m s?1. The collagen matrix of the penis is very thin and not arranged in an axial-orthogonal array, resulting in a penis that is flexible when erect. To test the hypothesis that female genital novelties make intromission difficult during forced copulations, we investigated penile eversion into glass tubes that presented different mechanical challenges to eversion. Eversion occurred successfully in a straight tube and a counterclockwise spiral tube that matched the chirality of the waterfowl penis, but eversion was significantly less successful into glass tubes with a clockwise spiral or a 135° bend, which mimicked female vaginal geometry. Our results support the hypothesis that duck vaginal complexity functions to exclude the penis during forced copulations, and coevolved with the waterfowl penis via antagonistic sexual conflict.
