Department of Genetics, University of Georgia, Athens, GA 30602.
Proc Natl Acad Sci U S A. 1989 Jan;86(2):573-6. doi: 10.1073/pnas.86.2.573.
Green turtles (Chelonia mydas) that nest on Ascension Island, in the south-central Atlantic, utilize feeding grounds along the coast of Brazil, more than 2000 km away. To account for the origins of this remarkable migratory behavior, Carr and Coleman [Carr, A. & Coleman, P. J. (1974) Nature (London) 249, 128-130] proposed a vicariant biogeographic scenario involving plate tectonics and natal homing. Under the Carr-Coleman hypothesis, the ancestors of Ascension Island green turtles nested on islands adjacent to South America in the late Cretaceous, soon after the opening of the equatorial Atlantic Ocean. Over the last 70 million years, these volcanic islands have been displaced from South America by sea-floor spreading, at a rate of about 2 cm/year. A population-specific instinct to migrate to Ascension Island is thus proposed to have evolved gradually over tens of millions of years of genetic isolation. Here we critically test the Carr-Coleman hypothesis by assaying genetic divergence among several widely separated green turtle rookeries. We have found fixed or nearly fixed mitochondrial DNA (mtDNA) restriction site differences between some Atlantic rookeries, suggesting a severe restriction on contemporary gene flow. Data are consistent with a natal homing hypothesis. However, an extremely close similarity in overall mtDNA sequences of surveyed Atlantic green turtles from three rookeries is incompatible with the Carr-Coleman scenario. The colonization of Ascension Island, or at least extensive gene flow into the population, has been evolutionarily recent.
在中大西洋的阿森松岛筑巢的绿海龟利用了距离 2000 多公里远的巴西沿海的觅食地。为了解释这种非凡的迁徙行为的起源，卡尔和科尔曼[Carr, A. & Coleman, P. J. (1974) Nature (London) 249, 128-130]提出了一个涉及板块构造和出生地归巢的趋异生物地理情景。根据卡尔-科尔曼假说，阿森松岛绿海龟的祖先在白垩纪晚期，即赤道大西洋开放后不久，就在南美洲附近的岛屿上筑巢。在过去的 7000 万年里，这些火山岛由于海底扩张，每年以大约 2 厘米的速度从南美洲漂移。因此，人们提出了一种种群特有的迁徙到阿森松岛的本能，这种本能是在数千万年的遗传隔离中逐渐进化而来的。在这里，我们通过检测几个分布广泛的绿海龟筑巢地之间的遗传差异，对卡尔-科尔曼假说进行了严格的检验。我们发现，一些大西洋筑巢地的线粒体 DNA（mtDNA）限制酶切位点存在固定或几乎固定的差异，这表明当代基因流受到严重限制。数据与出生地归巢假说一致。然而，在三个筑巢地的调查中，大西洋绿海龟的整体 mtDNA 序列非常相似，这与卡尔-科尔曼的情景不一致。阿森松岛的殖民化，或者至少是种群的广泛基因流，是最近才发生的进化事件。
