Downie D A, Fisher J R, Granett J
Department of Entomology, University of California, Davis 95616, USA.
Evolution. 2001 Jul;55(7):1345-62.
Studies of patterns of molecular variation in natural populations can provide important insights into a number of evolutionary problems. Among these, the question of whether geographic factors are more important than ecological factors in promoting population differentiation and ultimately speciation has been an important and contentious area in evolutionary biology. Systems involving herbivorous insects have played a leading role in this discussion. This study examined the distribution of molecular variation in a highly specialized gall-forming insect, grape phylloxera (Daktulosphaira vitifoliae Fitch), that is found on both sympatric and allopatric host-plant species of the genus Vitis. In addition, the relationship of insects in the introduced range in the United States to ancestral populations in the native range was examined. Evidence for differentiation along host-plant lines from both nuclear (RAPD) and mitochondrial (COI) DNA was confounded with the effect of geography. Differentiation was found where hosts were allopatric or parapatric, but no evidence was found for such differentiation on two hosts, V. vulpina and V. aestivalis, that are broadly sympatric. The question of population differentiation onto these sympatric hosts can be considered to be resolved--it has not occurred in spite of a long history of association. Evidence was equivocal, but suggestive of a period of divergence in allopatry prior to reestablishment of contact, for insects associated with another host plant species, V. cinerea, found in both sympatric and parapatric populations. A low level of diversity and placement of samples collected from the grape species V. riparia at the tip of a phylogenetic tree supports the hypothesis that this host has been recently colonized from populations from the Mississippi Valley. A polyphyletic origin for biotype B grape phylloxera was supported: Although most samples collected from vineyards in the introduced range in California had similar haplotypes, they were closely related to natives on V. vulpina from the Atlantic Coast-Piedmont region. All samples collected from vineyards in Oregon and Washington were closely related to natives on V. riparia in the northern United States.
对自然种群分子变异模式的研究能够为诸多进化问题提供重要见解。其中，在促进种群分化并最终导致物种形成的过程中，地理因素是否比生态因素更为重要这一问题，一直是进化生物学中一个重要且存在争议的领域。涉及植食性昆虫的系统在这一讨论中发挥了主导作用。本研究调查了一种高度特化的形成虫瘿的昆虫——葡萄根瘤蚜（Daktulosphaira vitifoliae Fitch）的分子变异分布情况，该昆虫存在于葡萄属的同域和异域寄主植物物种上。此外，还研究了美国引入区域的昆虫与原生区域祖先种群之间的关系。来自核（RAPD）和线粒体（COI）DNA的沿寄主植物谱系分化的证据与地理效应相互混淆。在寄主为异域或邻域分布的情况下发现了分化现象，但在广泛同域分布的两种寄主植物——狐葡萄（V. vulpina）和夏葡萄（V. aestivalis）上，未发现此类分化的证据。可以认为，关于这些同域寄主上的种群分化问题已经得到解决——尽管它们长期共生，但并未发生分化。对于同域和邻域种群中与另一种寄主植物物种——灰葡萄（V. cinerea）相关的昆虫，证据并不明确，但暗示在重新建立接触之前存在一段异域分化期。从葡萄物种河岸葡萄（V. riparia）采集的样本多样性较低且位于系统发育树顶端，这支持了该寄主最近是从密西西比河谷种群中殖民而来的假设。支持了生物型B葡萄根瘤蚜的多系起源：尽管从加利福尼亚引入区域的葡萄园采集的大多数样本具有相似的单倍型，但它们与来自大西洋海岸 - 皮埃蒙特地区狐葡萄上的本地种群密切相关。从俄勒冈州和华盛顿州葡萄园采集的所有样本都与美国北部河岸葡萄上的本地种群密切相关。
