McLain D K, Li J, Oliver J H
Biology Department, PO Box 8042, Georgia Southern University, Statesboro, Georgia 30460, USA.
Heredity (Edinb). 2001 Feb;86(Pt 2):234-42. doi: 10.1046/j.1365-2540.2001.00835.x.
The base sequence of the rDNA D3 expansion segment and flanking H14 stem varies between six species of Ixodes ticks (Acari: Ixodidae) where only 33 invariant sites occur among sequences of 123-203 bases in length. Multiple copies of D3 were sequenced from localities across the geographical ranges of four species to investigate deep population genetic structure. Two species, I. pacificus, from western North America, and I. ricinus, from Europe, have no sequence variation indicating a lack of deep genetic structure. One species, I. scapularis, from eastern North America has two forms of the D3 sequence that are distributed differently among northern vs. southern populations, suggesting recent divergence and hybridization. I. persulcatus, from Eurasia, has sequence variation between localities of the order of that observed between other species, suggesting a long history of population isolation and deep genetic structure. With the exception of I. scapularis, sequence variation was not observed within localities. This indicates that cellular processes underpinning concerted evolution have homogenized populations and species for particular rDNA sequence variants.
在六种硬蜱（蜱螨目：硬蜱科）中，核糖体DNA（rDNA）D3扩展片段和侧翼H14茎的碱基序列存在差异，在长度为123 - 203个碱基的序列中仅出现33个不变位点。从四个物种地理分布范围内的不同地点对多个D3拷贝进行测序，以研究深层种群遗传结构。来自北美西部的太平洋硬蜱（Ixodes pacificus）和来自欧洲的蓖麻硬蜱（Ixodes ricinus）这两个物种没有序列变异，表明缺乏深层遗传结构。来自北美东部的肩突硬蜱（Ixodes scapularis）有两种形式的D3序列，在北部和南部种群中的分布不同，这表明近期存在分化和杂交。来自欧亚大陆的全沟硬蜱（Ixodes persulcatus），其不同地点之间的序列变异程度与其他物种之间观察到的相似，表明其种群隔离历史悠久且具有深层遗传结构。除肩突硬蜱外，在各个地点内未观察到序列变异。这表明支持协同进化的细胞过程已经使特定rDNA序列变体的种群和物种同质化。
