Reeb C A, Avise J C
Department of Genetics, University of Georgia, Athens 30602.
Genetics. 1990 Feb;124(2):397-406. doi: 10.1093/genetics/124.2.397.
Restriction site variation in mitochondrial DNA (mtDNA) of the American oyster (Crassostrea virginica) was surveyed in continuously distributed populations sampled from the Gulf of St. Lawrence, Canada, to Brownsville, Texas. mtDNA clonal diversity was high, with 82 different haplotypes revealed among 212 oysters with 13 endonucleases. The mtDNA clones grouped into two distinct genetic arrays (estimated to differ by about 2.6% in nucleotide sequence) that characterized oysters collected north vs. south of a region on the Atlantic mid-coast of Florida. The population genetic "break" in mtDNA contrasts with previous reports of near uniformity of nuclear (allozyme) allele frequencies throughout the range of the species, but agrees closely with the magnitude and pattern of mtDNA differentiation reported in other estuarine species in the southeastern United States. This concordance of mtDNA phylogenetic pattern across independently evolving species provides strong evidence for vicariant biogeographic processes in initiating intraspecific population structure. The post-Miocene ecological history of the region suggests that reduced precipitation levels in an enlarged Floridian peninsula may have created discontinuities in suitable estuarine habitat for oysters during glacial periods, and that today such population separations are maintained by the combined influence of ecological gradients and oceanic currents on larval dispersal. The results are consistent with the hypothesis that historical vicariant events, in conjunction with contemporary environmental influences on gene flow, can result in genetic discontinuities in continuously distributed species with high dispersal capability.
对美洲牡蛎（Crassostrea virginica）线粒体DNA（mtDNA）的限制性酶切位点变异进行了调查，样本取自加拿大圣劳伦斯湾至得克萨斯州布朗斯维尔连续分布的种群。mtDNA克隆多样性很高，在212个牡蛎中用13种核酸内切酶检测到82种不同的单倍型。mtDNA克隆分为两个不同的遗传阵列（估计核苷酸序列差异约为2.6%），这两个阵列分别表征了在佛罗里达大西洋中部海岸一个区域以北和以南采集的牡蛎。mtDNA中的种群遗传“断点”与之前关于该物种整个分布范围内核（等位酶）等位基因频率近乎一致的报道形成对比，但与美国东南部其他河口物种报道的mtDNA分化程度和模式密切相符。这种跨独立进化物种的mtDNA系统发育模式的一致性为引发种内种群结构的间断生物地理过程提供了有力证据。该地区中新世后的生态历史表明，在冰川期，佛罗里达半岛扩大导致降水量减少，可能造成了适合牡蛎生存的河口栖息地的间断，而如今这种种群隔离是由生态梯度和洋流对幼虫扩散的综合影响维持的。结果与以下假设一致：历史上的间断事件，连同当代环境对基因流动的影响，可导致具有高扩散能力的连续分布物种出现遗传间断。
