Meyers Meredith K, Pankey M Sabrina, Wares John P
Odum School of Ecology, University of Georgia, Athens, Georgia, USA.
Rev Biol Trop. 2013 Mar;61(1):75-88. doi: 10.15517/rbt.v61i1.10886.
A large section of the tropical Eastern Pacific coastline is nearly devoid of reef or consolidated habitat, and is known as the Central American Gap as it is associated with a biogeographic transition in fish and invertebrate species. We analyze phylogeographic data for intertidal barnacles (Chthamalus) to identify relevant temporal patterns that describe the origins of this biogeographic transition (the Mexican-Panamic Transition Zone). These contrasts of populations on either side of the transition zone include two pairs of closely related species (C. panamensis and C. hedgecocki; C. southwardorum and a Southern form of C. southwardorum), as well as gene flow data within one species (C. panamensis) that currently is found on both sides of the boundary between provinces. Using sequence data from a prior phylogenetic study, we used traditional (net nucleotide divergence) measures as well as coalescent analyses that incorporate the isolation-migration model to identify the likely time of separation between Northern and Southern taxa in two species pairs. A total of 67 individuals were sequenced at two mitochondrial (cytochrome c oxidase I, 16S) and one nuclear (elongation factor 1-alpha) gene regions. Our analyses indicate that the regional isolation of these intertidal barnacles occurred approximately 315-400kya, with subsequent expansion of C. panamensis from the Southern region into the North much more recently. There are insufficient survey data to conclusively document the absence of species from this group within the Central American Gap region near the Gulf of Tehuantepec. However, appropriate habitat is quite sparse in this region and other environmental factors, including upwelling and water temperature, are likely to be associated with isolation of many species in the Mexican and Panamic provinces sensu stricto. Some taxa may maintain gene flow across this region, but very few genetic studies have been completed on such taxa. Until further work is done, distinguishing between prior hypotheses of a faunal gap, or a faunal transition zone, is somewhat speculative. Additional taxonomic revision will be necessary in Chthamalus but is beyond the scope of this paper.
热带东太平洋海岸线的很大一部分几乎没有珊瑚礁或固结栖息地，因其与鱼类和无脊椎动物物种的生物地理过渡相关，被称为中美洲间隙。我们分析潮间带藤壶（Chthamalus）的系统地理学数据，以确定描述这种生物地理过渡（墨西哥-巴拿马过渡区）起源的相关时间模式。过渡区两侧种群的这些对比包括两对密切相关的物种（巴拿马藤壶和赫奇科克藤壶；南下藤壶和南下藤壶的南方形态），以及目前在省界两侧都能找到的一个物种（巴拿马藤壶）内的基因流数据。利用先前系统发育研究的序列数据，我们使用传统（净核苷酸分歧）测量方法以及纳入隔离-迁移模型的溯祖分析，来确定两个物种对中北方和南方类群之间可能的分离时间。在两个线粒体（细胞色素c氧化酶I、16S）和一个核（延伸因子1-α）基因区域对总共67个个体进行了测序。我们的分析表明，这些潮间带藤壶的区域隔离大约发生在31.5-40万年前，随后巴拿马藤壶从南方地区向北方的扩张则要近得多。没有足够的调查数据来确凿地证明在特万特佩克湾附近的中美洲间隙区域内该类群物种的缺失。然而，该区域适宜的栖息地非常稀少，其他环境因素，包括上升流和水温，可能与墨西哥和严格意义上的巴拿马省许多物种的隔离有关。一些类群可能在该区域维持基因流，但针对此类类群完成的遗传研究很少。在进一步开展工作之前，区分先前关于动物区系间隙或动物区系过渡区的假设多少有些推测性。在藤壶属中还需要进行更多的分类修订，但这超出了本文的范围。
