Center for Conservation and Evolutionary Genetics, National Zoological Park and National Museum of Natural History, Smithsonian Institution, Washington, DC 20008, USA.
Proc Biol Sci. 2011 Mar 22;278(1707):817-25. doi: 10.1098/rspb.2010.1342. Epub 2010 Sep 22.
The Galapagos Islands are renowned for their high degree of endemism. Marine taxa inhabiting the archipelago might be expected to be an exception, because of their utilization of pelagic habitats-the dispersal barrier for terrestrial taxa-as foraging grounds. Magnificent frigatebirds (Fregata magnificens) have a highly vagile lifestyle and wide geographical distribution around the South and Central American coasts. Given the potentially high levels of gene flow among populations, the species provides a good test of the effectiveness of the Galapagos ecosystem in isolating populations of highly dispersive marine species. We studied patterns of genetic (mitochondrial DNA, microsatellites and nuclear introns) and morphological variation across the distribution of magnificent frigatebirds. Concordant with predictions from life-history traits, we found signatures of extensive gene flow over most of the range, even across the Isthmus of Panama, which is a major barrier to gene flow in other tropical seabirds. In contrast, individuals from the Galapagos were strongly differentiated from all conspecifics, and have probably been isolated for several hundred thousand years. Our finding is a powerful testimony to the evolutionary uniqueness of the taxa inhabiting the Galapagos archipelago and its associated marine ecosystems.
加拉帕戈斯群岛以其高度的特有性而闻名。栖息在群岛中的海洋分类群可能是一个例外，因为它们利用了远洋栖息地——作为陆地分类群扩散障碍的觅食地。壮丽的军舰鸟（Fregata magnificens）具有高度迁徙的生活方式和广泛的地理分布范围，在南美和中美海岸周围。鉴于种群之间可能存在高水平的基因流动，该物种很好地检验了加拉帕戈斯生态系统在隔离高度扩散的海洋物种种群方面的有效性。我们研究了壮丽军舰鸟在分布范围内的遗传（线粒体 DNA、微卫星和核内含子）和形态变异模式。与生活史特征的预测一致，我们发现了在大多数范围内广泛基因流动的迹象，甚至跨越了巴拿马地峡，这是其他热带海鸟基因流动的主要障碍。相比之下，来自加拉帕戈斯群岛的个体与所有同种个体明显不同，并且可能已经隔离了数十万年。我们的发现有力地证明了栖息在加拉帕戈斯群岛及其相关海洋生态系统中的分类群的进化独特性。
