Sword G A, Joern A, Senior L B
Northern Plains Agricultural Research Laboratory, United States Department of Agriculture, Agricultural Research Service, 1500 N. Central Ave., Sidney, MT, 59270, USA.
Mol Ecol. 2005 Jun;14(7):2197-205. doi: 10.1111/j.1365-294X.2005.02546.x.
Studies of herbivorous insects have played a major role in understanding how ecological divergence can facilitate genetic differentiation. In contrast to the majority of herbivorous insects, grasshoppers as a group are largely polyphagous. Due to this relative lack of intimate grasshopper-plant associations, grasshopper-plant systems have not played a large part in the study of host-associated genetic differentiation. The oligophagous grasshopper, Hesperotettix viridis (Thomas), is endemic to North America and feeds on composites (Asteraceae) within the tribe Astereae. Previous work has shown both preference and performance differences between H. viridis individuals feeding on either Solidago mollis or Gutierrezia sarothrae. Using 222 AFLP markers, we examined the genetic relationships among 38 H. viridis individuals feeding on these plants both in sympatry and allopatry. Neighbour-joining analysis resulted in two distinct host-associated clades with 71% bootstrap support for host-associated monophyly. Analyses of molecular variation (amova) revealed significant genetic structuring with host plant accounting for 20% of the total genetic variance while locality accounted for 0%. Significant genetic differentiation was detected between S. mollis-feeders and G. sarothrae-feeders even when the two were present at the same locality. These results are consistent with observed differences in preference and performance between H. viridis grasshoppers feeding on either G. sarothrae or S. mollis and indicate that H. viridis is comprised of at least two genetically distinct host plant-associated lineages.
对植食性昆虫的研究在理解生态分化如何促进遗传分化方面发挥了重要作用。与大多数植食性昆虫不同，蝗虫作为一个群体在很大程度上是多食性的。由于蝗虫与植物之间相对缺乏紧密的关联，蝗虫 - 植物系统在宿主相关遗传分化的研究中并未发挥重要作用。寡食性蝗虫绿拟蝗（Hesperotettix viridis，托马斯）原产于北美，以紫菀族（菊科）内的菊科植物为食。先前的研究表明，以软毛一枝黄花（Solidago mollis）或蛇鞭菊（Gutierrezia sarothrae）为食的绿拟蝗个体之间存在偏好和表现差异。我们使用222个AFLP标记，研究了38只在同域和异域以这些植物为食的绿拟蝗个体之间的遗传关系。邻接法分析产生了两个不同的宿主相关分支，对宿主相关单系性有71%的自展支持。分子变异分析（AMOVA）揭示了显著的遗传结构，宿主植物占总遗传变异的20%，而地理位置占0%。即使软毛一枝黄花取食者和蛇鞭菊取食者出现在同一地点，也检测到它们之间存在显著的遗传分化。这些结果与观察到的以蛇鞭菊或软毛一枝黄花为食的绿拟蝗在偏好和表现上的差异一致，并表明绿拟蝗至少由两个遗传上不同的宿主植物相关谱系组成。
