善于航海的維京人，壯舉之一就是橫跨大西洋。但在維京人之前數(shù)百萬年,，鱷魚就已經(jīng)乘風(fēng)破浪，跋涉數(shù)千公里,，從非洲到達(dá)了美洲繁衍,。今天，鱷屬（Crocodylus）的動物已經(jīng)遍布四海,。
圖：漂洋過海的鱷魚
來自紐約福德姆大學(xué)（Fordham University）的E.Hekkala及其同事利用鱷屬11個種的線粒體DNA,，建立了完整的鱷屬演化樹，從而得出了以上結(jié)論,。11個種中的8個，之前都沒有進(jìn)行過線粒體DNA測序,。
研究發(fā)現(xiàn),，美洲的4種鱷魚都與東非的尼羅鱷親緣最近，它們在700萬年前開始分異,，這一時間遠(yuǎn)晚于非洲大陸和南美洲分裂的時間（1.3億年前）,。700萬年前，非洲鱷魚所面對的是2800多公里的大海,。
盡管古生物學(xué)家們一直猜測鱷魚漂洋過海并扎根美洲,，但一直沒有確鑿證據(jù)。Hekkala的發(fā)現(xiàn)讓鱷魚遠(yuǎn)渡重洋的情景更加有說服力了,。
鱷魚能在咸水體中生活,，最多可以堅(jiān)持6個月不進(jìn)食。更令人稱奇的是,，在交配完成之后,，雌性可以將精子保存在體內(nèi)達(dá)數(shù)月之久,，因此一旦一只受精雌性游過了大西洋，這一物種便能在新的土地上扎根了,。雖然一兩次的漂洋過海并不足以演化出所有種類的美洲鱷,，但Hekkala指出，動物可以乘著向西的赤道洋流,，從非洲海岸到達(dá)美洲,，所以鱷類穿越大西洋到達(dá)美洲并形成規(guī)模，還是很有可能的,。（生物谷Bioon.com）
生物谷推薦原文出處：
Marine Biology DOI: 10.1007/s00227-009-1174-5
Between introgression events and fragmentation, islands are the last refuge for the American crocodile in Caribbean Mexico
Salima Machkour-M’Rabet, Yann Hénaut, Pierre Charruau, Muriel Gevrey, Peter Winterton and Luc Legal
Habitat loss and degradation in the Mexican Caribbean, caused by the development of tourism, have decreased the potential nesting area for the American crocodile (Crocodylus acutus) and have fragmented the populations of the Yucatan peninsula. Our study investigated five populations (three continental: North, South, Sian Ka’an, and two insular: Cozumel, Banco Chinchorro) of C. acutus in the Mexican Caribbean using seven different inter simple sequence repeat (ISSR) markers as tools for genetic variability and population differentiation. Three classification methods were tested and compared: distance analysis, self-organizing map, and Bayesian methods, to evaluate the resolution of each method with ISSR markers. The 77 loci selected revealed a high variability between populations (polymorphism from 17% for Sian Ka’an to 75% for Banco Chinchorro) with a total polymorphism of 84% and a global coefficient of gene differentiation (G ST ) of 0.296, but low values of Nei’s Gene diversity (from 0.065 for Sian Ka’an to 0.233 for Banco Chinchorro). Our results suggest elevated inbreeding in all local populations with higher indices for Banco Chinchorro and lower indices for Sian Ka’an. Three independent classification methods gave similar results, and suggested that most continental individuals are admixtures, with different levels of introgression, with the sympatric species Crocodylus moreletii. We propose that the islands/atolls remain the sole areas with genetically “pure” American crocodiles and we discuss these results for future conservation of this endangered crocodile species.
