Criscione Charles D, Blouin Michael S
Department of Zoology, Oregon State University, 3029 Cordley Hall, Corvallis, Oregon 97331, USA.
Evolution. 2004 Jan;58(1):198-202. doi: 10.1111/j.0014-3820.2004.tb01587.x.
Little is known about what controls effective sizes and migration rates among parasite populations. Such data are important given the medical, veterinary, and economic (e.g., fisheries) impacts of many parasites. The autogenic-allogenic hypothesis, which describes ecological patterns of parasite distribution, provided the foundation on which we studied the effects of life cycles on the distribution of genetic variation within and among parasite populations. The hypothesis states that parasites cycling only in freshwater hosts (autogenic life cycle) will be more limited in their dispersal ability among aquatic habitats than parasites cycling through freshwater and terrestrial hosts (allogenic life cycle). By extending this hypothesis to the level of intraspecific genetic variation, we examined the effects of host dispersal on parasite gene flow. Our a priori prediction was that for a given geographic range, autogenic parasites would have lower gene flow among subpopulations. We compared intraspecific mitochondrial DNA variation for three described species of trematodes that infect salmonid fishes. As predicted, autogenic species had much more highly structured populations and much lower gene flow among subpopulations than an allogenic species sampled from the same locations. In addition, a cryptic species was identified for one of the autogenic trematodes. These results show how variation in life cycles can shape parasite evolution by predisposing them to vastly different genetic structures. Thus, we propose that knowledge of parasite life cycles will help predict important evolutionary processes such as speciation, coevolution, and the spread of drug resistance.
对于控制寄生虫种群有效规模和迁移率的因素，我们知之甚少。鉴于许多寄生虫对医学、兽医和经济（如渔业）的影响，这些数据非常重要。自生性 - 异生性假说描述了寄生虫分布的生态模式，为我们研究生命周期对寄生虫种群内部和种群间遗传变异分布的影响提供了基础。该假说指出，仅在淡水宿主中循环的寄生虫（自生性生命周期）在水生栖息地之间的扩散能力比通过淡水和陆地宿主循环的寄生虫（异生性生命周期）更受限制。通过将这一假说扩展到种内遗传变异水平，我们研究了宿主扩散对寄生虫基因流动的影响。我们的先验预测是，在给定的地理范围内，自生性寄生虫在亚种群之间的基因流动会更低。我们比较了三种已描述的感染鲑科鱼类的吸虫的种内线粒体DNA变异。正如预测的那样，与从相同地点采样的异生性物种相比，自生性物种的种群结构更为高度结构化，亚种群之间的基因流动更低。此外，我们还鉴定出一种自生性吸虫的隐存种。这些结果表明，生命周期的差异如何通过使寄生虫倾向于具有截然不同的遗传结构来塑造寄生虫的进化。因此，我们认为了解寄生虫的生命周期将有助于预测重要的进化过程，如物种形成、协同进化和耐药性的传播。
