Departamento de Xenética, Universidade de Santiago de Compostela, Facultade de Veterinaria, Campus de Lugo, 27002 Lugo, Spain.
Infect Genet Evol. 2012 Jan;12(1):45-52. doi: 10.1016/j.meegid.2011.10.010. Epub 2011 Oct 22.
Twelve polymorphic genetic markers, eight allozymic loci and four microsatellites, were used to characterize 20 infrapopulations of Fasciola hepatica (all flukes from 10 individual cattle and 10 sheep) from 11 farms in Northwest Spain. Results suggest different patterns of population genetic structure depending on the host species. Individuals identified as clones were much more frequent in sheep. The common presence of clones and its nonrandom occurrence among individual hosts suggests clumped transmission of liver flukes in sheep. After reducing significant repeated multilocus genotypes to one unique copy within infrapopulations, results show relatively high levels of gene diversity within infrapopulations from cattle and sheep (0.411 and 0.360 on average, respectively). However, parasites of sheep appear to show significantly more structured variation at the infrapopulation level (Standardized F(ST)=0.087 and 0.170 for parasites of cattle and sheep, respectively). Compared to the parasites from cattle, results suggest that populations from sheep show lower levels of gene flow, higher degree of aggregate transmission, higher probability of mating within clones, and lower parasitic load. These differences have implications for the evolution of anthelmintic resistance because they affect the effective population size and the degree of inbreeding. The development and rapid spread of resistance seems likely in the parasites of cattle because populations from the study area are characterized by high gene flow. However, results also suggest that the efficient selection of a new recessive advantageous mutation would be favored in parasites of sheep due to a greater potential for inbreeding.
利用 12 个多态性遗传标记、8 个等位基因座和 4 个微卫星，对来自西班牙西北部 11 个农场的 20 个 Fasciola hepatica （均为来自 10 头牛和 10 只羊的吸虫）亚种群进行了特征描述。结果表明，宿主物种不同，种群遗传结构模式也不同。绵羊中克隆个体的出现频率明显更高。克隆的普遍存在及其在个体宿主中的非随机出现表明，绵羊肝吸虫的传播呈聚集性。在将显著的多基因座基因型重复减少到亚种群内的一个独特副本后，结果显示牛和羊的亚种群内具有相对较高的基因多样性（平均分别为 0.411 和 0.360）。然而，绵羊寄生虫在亚种群水平上的变异似乎具有显著的结构特征（牛和羊的寄生虫的标准化 F(ST)分别为 0.087 和 0.170）。与来自牛的寄生虫相比，结果表明，来自绵羊的种群表现出较低的基因流、更高的聚集传播程度、更高的克隆内交配概率和更低的寄生虫负荷。这些差异对驱虫剂耐药性的进化具有重要意义，因为它们影响有效种群大小和近亲繁殖程度。由于研究区域的种群具有高基因流，因此牛寄生虫的耐药性发展和迅速传播似乎很有可能。然而，结果还表明，由于近亲繁殖的潜力更大，绵羊寄生虫中有利隐性突变的有效选择将更有利。
