La Rosa G, Marucci G, Zarlenga D S, Casulli A, Zarnke R L, Pozio E
Laboratory of Parasitology, Istituto Superiore di Sanità, viale Regina Elena 299, 00161 Rome, Italy.
Int J Parasitol. 2003 Feb;33(2):209-16. doi: 10.1016/s0020-7519(02)00258-8.
To date, there are no data available on the population genetics of Trichinella due to the lack of genetic markers and the difficulty of working with such small parasites. In the Arctic region of North America and along the Rocky Mountains, there exist two genotypes of Trichinella, Trichinella nativa and Trichinella T6, respectively, which are well differentiated by biochemical and molecular characters. However, both are resistant to freezing, show other common biological characters (e.g. low or no infectivity to rodents and swine) and produce fertile F1 offspring upon interbreeding. To data, these two genotypes have been considered allopatric. In this study, we detected both genotypes in wolves of the same wolf packs in Alaska, suggesting sympatry. A single GTT trinucleotide present in the ITS-2 sequence of T. nativa but not in Trichinella T6 was used as a genetic marker to study gene flow for this character in both a murine infection model and in larvae from naturally-infected Alaskan wolves. Only F1 larvae originating from a cross between T. nativa male and Trichinella T6 female were able to produce F2 offspring. Larvae (F1) originating from a cross between Trichinella T6 male and T. nativa female were not reproductively viable. As expected, all F1 larvae showed a heterozygote pattern for the GTT character upon heteroduplex analysis; however, within the F2 population, the number of observed heterozygotes (n=52) was substantially higher than expected (n=39.08), as supported by the F(is) index, and was not in the Hardy-Weinberg equilibrium. Larvae from two of the 16 Trichinella positive Alaskan wolves, showed the Trichinella T6 pattern or the T. nativa/Trichinella T6 hybrid pattern. Our data demonstrate that T. nativa and Trichinella T6 live in sympatry at least in Alaskan wolves, where T. nativa occurs more frequently (69%) than Trichinella T6 (31%). One explanation for this phenomenon is that glacial periods may have caused a geographical relocation, colonisation and independent evolution of T. nativa within the Rocky Mountains, resulting in a bifurcation of the freeze-resistant genotype. Additional studies will be required to test this hypothesis.
迄今为止，由于缺乏遗传标记以及处理如此微小寄生虫的困难，关于旋毛虫种群遗传学尚无可用数据。在北美北极地区和落基山脉沿线，分别存在两种旋毛虫基因型，即本地旋毛虫和旋毛虫T6，它们在生化和分子特征上有明显差异。然而，两者都对冷冻有抗性，表现出其他共同的生物学特征（如对啮齿动物和猪的感染性低或无感染性），并且杂交时能产生可育的F1后代。到目前为止，这两种基因型被认为是异域分布的。在本研究中，我们在阿拉斯加同一狼群的狼体内检测到了这两种基因型，表明它们是同域分布的。本地旋毛虫ITS - 2序列中存在而旋毛虫T6中不存在的单个GTT三核苷酸被用作遗传标记，以研究在小鼠感染模型和自然感染的阿拉斯加狼幼虫中该性状的基因流动。只有来自本地旋毛虫雄性与旋毛虫T6雌性杂交的F1幼虫能够产生F2后代。来自旋毛虫T6雄性与本地旋毛虫雌性杂交的幼虫没有生殖能力。正如预期的那样，所有F1幼虫在异源双链分析中显示出GTT性状的杂合子模式；然而，在F2群体中，观察到的杂合子数量（n = 52）显著高于预期（n = 39.08），F(is)指数支持这一点，并且不符合哈迪 - 温伯格平衡。16只旋毛虫阳性阿拉斯加狼中有两只的幼虫显示出旋毛虫T6模式或本地旋毛虫/旋毛虫T6杂交模式。我们的数据表明，本地旋毛虫和旋毛虫T6至少在阿拉斯加狼中是同域分布的，其中本地旋毛虫出现的频率（69%）高于旋毛虫T6（31%）。对这一现象的一种解释是，冰川期可能导致了本地旋毛虫在落基山脉内的地理迁移、定殖和独立进化，从而导致了抗冻基因型的分歧。需要进一步的研究来验证这一假设。
