Animal Parasitic Disease Laboratory, Agricultural Research Service, US Department of Agriculture, Henry A Wallace Agricultural Research Center, Beltsville, MD 20705, United States.
Infect Genet Evol. 2012 Dec;12(8):1605-13. doi: 10.1016/j.meegid.2012.06.007. Epub 2012 Jun 26.
The evolutionary history and epidemiology of parasites may be reflected in the extent and geographic distribution of their genetic variation. Among coccidian parasites, the population structure of only Toxoplasma gondii has been extensively examined. Intraspecific variation in other coccidia, for example, those assigned to the genus Besnoitia, remains poorly defined. Here, we characterize the extent of genetic variation among populations of Besnoitia tarandi, a parasite whose intermediate hosts include reindeer/caribou (Rangifer tarandus). Isolates from the Canadian Arctic and Finnish sub-Arctic were genotyped at six microsatellite loci, the first internal transcribed spacer region of nuclear rDNA, and the RNA polymerase β subunit (rpoB) encoded in the plastid genome. Remarkably, all isolates exhibited the same multilocus genotype, regardless of the isolate's geographic origin. This absolute monomorphism occurred despite the capacity of these loci to vary, as established by evident differentiation between B. tarandi and two other species of Besnoitia, and variation among four isolates of B. besnoiti. The surprising lack of genetic variation across the sampled range suggests that B. tarandi may have experienced a recent population bottleneck.
寄生虫的进化历史和流行病学可能反映在其遗传变异的程度和地理分布上。在球虫寄生虫中，只有刚地弓形虫的种群结构得到了广泛研究。其他球虫，例如属于贝氏科的那些，其种内变异仍然定义不明确。在这里，我们描述了 Besnoitia tarandi 种群的遗传变异程度，Besnoitia tarandi 的中间宿主包括驯鹿/北美驯鹿（Rangifer tarandus）。来自加拿大北极和芬兰亚北极的分离株在六个微卫星基因座、核 rDNA 的第一内部转录间隔区和质体基因组编码的 RNA 聚合酶β亚基（rpoB）上进行了基因分型。值得注意的是，无论分离株的地理起源如何，所有分离株都表现出相同的多位点基因型。尽管这些基因座具有变异的能力，如通过 B. tarandi 与其他两种 Besnoitia 物种之间的明显分化以及 B. besnoiti 的四个分离株之间的变异来证明，但这种绝对的同态性仍然存在。在所采样范围内缺乏遗传变异的情况令人惊讶，这表明 B. tarandi 可能经历了最近的种群瓶颈。
