Benzie John A H, Williams Suzanne T
Australian Institute of Marine Science, PMB No 3, Townsville MC, Queensland, 4810, Australia.
Evolution. 1997 Jun;51(3):768-783. doi: 10.1111/j.1558-5646.1997.tb03660.x.
The Pacific marine biota, particularly species with long planktonic larval stages, are thought to disperse widely throughout the Pacific via ocean currents. The little genetic data available to date has supported this view in that little or no significant regional differentiation of populations has been found over large geographical distances. However, recent data from giant clams has demonstrated not only significant regional differentiation of populations, but routes of gene flow that run perpendicular to the main present-day ocean currents. Extensive surveys of genetic variation at eight polymorphic loci in 19 populations of the giant clam Tridacna maxima, sampled throughout the West and Central Pacific, confirmed that the patterns of variation seen so far in T. gigas were not unique to that species, and may reflect a fundamental genetic structuring of shallow-water marine taxa. Populations of T. maxima within highly connected reef systems like the Great Barrier Reef were panmictic (average F < 0.003), but highly significant genetic differences between reef groups on different archipelagos (average F = 0.084) and between West and Central Pacific regions (average F = 0.156) were found. Inferred gene flow was high (N m usually > 5) between the Philippines and the Great Barrier Reef, between the Philippines and Melanesia (the Solomon Islands and Fiji), and between the Philippines and the Central Pacific island groups (Marshall Islands, Kiribati, Tuvalu and Cook Islands). Gene flow was low between these three sets of island chains (N m < 2). These routes of gene flow are perpendicular to present-day ocean currents. It is suggested that the spatial patterns of gene frequencies reflect past episodes of dispersal at times of lower sea levels which have not been erased by subsequent dispersal by present-day circulation. The patterns are consistent with extensive dispersal of marine species in the Pacific, and with traditional views of dispersal from the Indo-Malay region. However, they demonstrate that dispersal along present-day ocean surface currents cannot be assumed, that other mechanisms may operate today or that major dispersal events are intermittent (perhaps separated by several thousands of years), and that the nature and timing of dispersal of Pacific marine species is more complex than has been thought.
太平洋海洋生物群落，尤其是那些具有较长浮游幼虫阶段的物种，被认为会通过洋流在整个太平洋广泛扩散。迄今为止可获得的少量遗传数据支持了这一观点，因为在大地理距离上几乎没有发现种群的显著区域分化。然而，最近来自巨型蛤蜊的数据不仅表明了种群的显著区域分化，还显示了与当今主要洋流垂直的基因流动路径。对整个西太平洋和中太平洋采集的19个大砗磲种群的8个多态位点的遗传变异进行的广泛调查证实，到目前为止在巨砗磲中看到的变异模式并非该物种所特有，可能反映了浅水海洋分类群的基本遗传结构。在像大堡礁这样高度连通的珊瑚礁系统中的大砗磲种群是随机交配的（平均F < 0.003），但在不同群岛的珊瑚礁群之间（平均F = 0.084）以及西太平洋和中太平洋地区之间（平均F = 0.156）发现了高度显著的遗传差异。推断在菲律宾和大堡礁之间、菲律宾和美拉尼西亚（所罗门群岛和斐济）之间以及菲律宾和中太平洋岛屿群（马绍尔群岛、基里巴斯、图瓦卢和库克群岛）之间基因流动很高（N m通常> 5）。这三组岛链之间的基因流动很低（N m < 2）。这些基因流动路径与当今的洋流垂直。有人认为，基因频率的空间模式反映了过去海平面较低时的扩散事件，这些事件并未被随后当今环流的扩散所消除。这些模式与太平洋海洋物种的广泛扩散以及从印度 - 马来地区扩散的传统观点一致。然而，它们表明不能假定沿着当今海洋表面洋流的扩散，可能存在其他当今起作用的机制，或者主要扩散事件是间歇性的（可能相隔数千年），并且太平洋海洋物种扩散的性质和时间比人们想象的更为复杂。
