Akimoto S
Entomological Institute, Faculty of Agriculture, Hokkaido University, 060, Sapporo, Japan.
Oecologia. 1990 Jun;83(2):162-70. doi: 10.1007/BF00317747.
The process of host race formation in the aphid Tetraneura yezoensis is examined in relation to its population structure. T. yezoensis induces pouch galls on new leaves of Ulmus davidiana and U. laciniata. Its populations on the two host species are often sympatric. Fundatrices found on one elm species, when reciprocally transplanted to the other, suffered greatly reduced average fitness. This shows that aphid populations associated with the two elm species are genetically differentiated in physiological traits. Individual trees of each elm species showed large differences in susceptibility to gall formation and in bud burst time, and such between-tree variations were consistent over years. Overwintered eggs taken in early spring from four trees (two from each species) were incubated under the same temperature conditions. The average hatching time differed significantly even between populations from conspecific trees, and the sequence of egg hatching paralleled that of the leafing of those four trees. This between-tree difference in hatching time was consistent over years and was found to be genetic, showing that gene flow between aphid populations on separate trees is often restricted. The heterogeneity in host traits may have promoted the evolution of philopatry in this aphid. Of the fundatrices that hatched on a tree of one elm species, a few precent were preadapted to gall formation on the other elm species. This suggests that the formation of a new host race proceeds parapatrically under disruptive selection and at a low level of gene flow. Evidence was actually obtained that a small fraction of Tetraneura alates are passively transported and land on non-host plants.
对蚜虫落叶松长足大蚜（Tetraneura yezoensis）宿主专化型形成过程与其种群结构的关系进行了研究。落叶松长足大蚜在蒙古榆（Ulmus davidiana）和裂叶榆（U. laciniata）的新叶上诱导形成囊状虫瘿。其在这两种宿主植物上的种群常同域分布。在一种榆树上发现的干母若蚜，相互移植到另一种榆树上时，平均适合度大幅降低。这表明与这两种榆树相关的蚜虫种群在生理特征上存在遗传分化。每种榆树的单株在形成虫瘿的易感性和芽萌发时间上表现出很大差异，而且这种树间差异多年来保持一致。早春从四棵树（每种两棵）采集的越冬卵在相同温度条件下孵化。即使是来自同种树木的种群，平均孵化时间也有显著差异，卵孵化顺序与这四棵树的展叶顺序一致。这种树间孵化时间差异多年来保持一致，且被发现是遗传的，表明不同树木上蚜虫种群之间的基因流动通常受到限制。宿主特征的异质性可能促进了这种蚜虫的留居习性进化。在一种榆树上孵化的干母若蚜中，有一小部分预先适应了在另一种榆树上形成虫瘿。这表明新宿主专化型的形成在间断选择和低水平基因流动下以邻域分布的方式进行。实际上有证据表明，一小部分落叶松长足大蚜有翅蚜会被被动运输并落在非宿主植物上。
