Animal Parasitic Disease Laboratory, Agricultural Research Service, USDA, Beltsville, MD 20705, United States.
Infect Genet Evol. 2012 Apr;12(3):530-8. doi: 10.1016/j.meegid.2012.01.004. Epub 2012 Jan 15.
The genetic diversity within and among parasite populations provides clues to their evolutionary history. Here, we sought to determine whether mitochondrial and microsatellite DNA variation could be used to evaluate the extent of differentiation, gene flow and historical reproductive isolation among the freeze resistant parasites Trichinella nativa and the Trichinella T6 genotype infecting wolverines (Gulo gulo) in Nunavut, Canada. To this end, we genotyped Trichinella isolates derived from the diaphragms of 39 wolverines from this locale to reference strains of T. nativa and the Trichinella T6 genotype. Results showed that among a subset of 13 isolates examined, individuals resembled T. nativa in their mitochondrial DNA, but resembled the Trichinella T6 genotype when assayed at expansion segment V and the internal transcribed spacer of the nuclear rDNA. To adjudicate among these conflicting diagnoses, we further characterized each isolate at several nuclear microsatellite loci and again compared these to data from reference strains. Statistical assignment established that the nuclear genomes of most Nunavut isolates corresponded to those of the Trichinella T6 genotype; however, two isolates corresponded to T. nativa, and one isolate exhibited equal similarity to both reference strains. Taken as a whole, the evidence suggests that these isolates derive from the T. nativa matrilineage, but that their nuclear genomes resemble individuals previously designated as Trichinella T6. Assuming distinct lineages, this argues for cross-hybridization among these genotypes. Although introgression has occurred, recognizable genetic distinctions persist. One possibility is that selection disfavors the survival of hybrid offspring in most instances. Alternatively, the recent disappearance of glacial barriers might have increased contact, and therefore introgression. Broader geographic sampling will be required to determine the extent to which hybridization occurs beyond this particular geographic focus.
寄生虫种群内和种群间的遗传多样性为其进化历史提供了线索。在这里，我们试图确定线粒体和微卫星 DNA 变异是否可用于评估在加拿大努纳武特省抗冻寄生虫旋毛虫和感染狼獾（Gulo gulo）的旋毛虫 T6 基因型之间的分化程度、基因流动和历史生殖隔离。为此，我们对来自该地区的 39 只狼獾膈肌中的旋毛虫分离株进行了基因分型，以参考株的旋毛虫和旋毛虫 T6 基因型。结果表明，在所检查的 13 个分离株的亚集中，个体在其线粒体 DNA 中与旋毛虫相似，但在扩增片段 V 和核 rDNA 的内部转录间隔区进行检测时与旋毛虫 T6 基因型相似。为了解决这些相互矛盾的诊断问题，我们进一步在几个核微卫星基因座上对每个分离株进行了特征描述，并将这些数据与参考株的数据进行了比较。统计分配确定，大多数努纳武特分离株的核基因组与旋毛虫 T6 基因型相对应；然而，有两个分离株与旋毛虫相对应，一个分离株与两个参考株都具有相似性。总的来说，证据表明这些分离株来自旋毛虫母系，但它们的核基因组与先前被指定为旋毛虫 T6 的个体相似。假设存在不同的谱系，这表明这些基因型之间存在杂交。尽管发生了基因渗入，但仍存在可识别的遗传差异。一种可能性是，在大多数情况下，选择不利于杂种后代的生存。或者，最近冰川屏障的消失可能增加了接触，从而增加了基因渗入。需要更广泛的地理采样来确定这种杂交在这一特定地理区域之外的发生程度。
