Hare Matthew P, Avise John C
Department of Genetics, University of Georgia, Athens, Georgia, 30602.
Evolution. 1996 Dec;50(6):2305-2315. doi: 10.1111/j.1558-5646.1996.tb03618.x.
Gulf of Mexico versus Atlantic populations of several coastal species in the southeastern United States are known to differ sharply in genetic composition, but most transitional zones have not previously been examined in detail. Here we employ molecular markers from mitochondrial and nuclear loci to characterize cytonuclear genetic associations at meso- and microgeographic scales along an eastern Florida transitional zone between genetically distinct Atlantic and Gulf populations of the American oyster, Crassostrea virginica. The single- and multilocus cytonuclear patterns display: (1) a cline extending along 340 km of the east Florida coastline; (2) a pronounced step in the cline centered at Cape Canaveral (shifts in allelic frequencies by 50-75% over a 20 km distance); (3) a close agreement of observed genotypic frequencies with Hardy-Weinberg expectations within locales; and (4) mild or nonexistent nuclear and cytonuclear disequilibria in most local population samples. These results imply: (1) considerable restrictions to interpopulational gene flow along the eastern Florida coastline; (2) within locales, free interbreeding (as opposed to mere population admixture) between Gulf and Atlantic forms of oysters; and (3) localized population recruitment in the transition zone localities. These findings demonstrate that marine organisms with high dispersal potential via long-lived pelagic larvae can nonetheless display pronounced spatial population genetic structure, and more generally they exemplify the utility of pronounced genetic transition zones for the study of population level processes.
美国东南部几种沿海物种在墨西哥湾与大西洋的种群，其基因组成差异显著，但此前大多数过渡区域尚未得到详细研究。在此，我们利用线粒体和核基因座的分子标记，来描述美国牡蛎（Crassostrea virginica）在佛罗里达州东部一个过渡区域内中尺度和微尺度上的细胞核基因关联，该区域介于基因上截然不同的大西洋种群和墨西哥湾种群之间。单基因座和多基因座的细胞核基因模式显示：（1）一条沿着佛罗里达州东部海岸线延伸340公里的渐变群；（2）渐变群在卡纳维拉尔角处有一个明显的阶梯（等位基因频率在20公里的距离内变化50 - 75%）；（3）在各个区域内，观察到的基因型频率与哈迪 - 温伯格预期值高度吻合；（4）在大多数当地种群样本中，核基因和细胞核基因的不平衡程度较轻或不存在。这些结果表明：（1）佛罗里达州东部海岸沿线种群间的基因流动受到相当大的限制；（2）在各个区域内，墨西哥湾和大西洋形态的牡蛎之间存在自由杂交（而非仅仅是种群混合）；（3）过渡区域的局部地点存在局部种群补充。这些发现表明，即使是具有通过长寿浮游幼虫进行高扩散潜力的海洋生物，也可能表现出明显的空间种群遗传结构，更广泛地说，它们例证了明显的遗传过渡区域在研究种群水平过程中的效用。
