Department of Forestry and Natural Resources, Purdue University, West Lafayette, IN 47907, USA.
Int J Parasitol. 2010 Jun;40(7):787-95. doi: 10.1016/j.ijpara.2009.12.004. Epub 2010 Jan 7.
The American dog tick (Dermacentor variabilis) is an important vector of numerous pathogens of humans and animals. In this study, we analysed population genetic patterns in D. variabilis at scales of the host individual (infrapopulation) and population (component population) to elucidate fine-scale spatial and temporal factors influencing transmission dynamics. We genotyped D. variabilis collected from raccoons (Procyon lotor) trapped in two habitat patches (located in Indiana, USA) which were spatially proximate (5.9 km) and limited in size (10.48 Ha and 25.47 Ha, respectively). Despite the fine spatial sampling scale, our analyses revealed significant genetic differentiation amongst component populations and infrapopulations (within each component population), indicating a non-random pattern of encountering tick genotypes by raccoons at both scales evaluated. We found evidence for male-biased dispersal in the ticks themselves (in one component population) and an age-bias in spatial scales at which raccoons encountered ticks in the environment. At the scale of the component population, our analyses revealed that raccoons encountered ticks from a limited number of D. variabilis family groups, likely due to high reproductive variance amongst individual ticks. Finally, we found evidence for a temporal effect with raccoons encountering ticks in the environment as "clumps" of related individuals. While the genetic structure of parasite populations are increasingly being investigated at small spatial scales (e.g. the infrapopulation), our data reveal that genetic structuring can originate at scales below that of the infrapopulation, due to the interaction between temporal and biological factors affecting the encounter of parasites by individual hosts. Ultimately, our data indicate that genetic structure in parasites must be viewed as a consequence of both spatial and temporal variance in host-parasite interactions, which in turn are driven by demographic factors related to both the host and parasite.
美洲犬蜱（Dermacentor variabilis）是人类和动物多种病原体的重要载体。在这项研究中，我们分析了美洲犬蜱在宿主个体（亚种群）和种群（组成种群）尺度上的种群遗传模式，以阐明影响传播动态的精细时空因素。我们对在印第安纳州两个生境斑块（相距 5.9 公里，面积分别为 10.48 公顷和 25.47 公顷）中捕获的浣熊（Procyon lotor）身上采集的美洲犬蜱进行了基因分型。尽管空间采样尺度很精细，但我们的分析表明，组成种群和亚种群（每个组成种群内）之间存在显著的遗传分化，这表明浣熊在两个评估尺度上遇到蜱基因型的模式是非随机的。我们发现，在蜱本身（在一个组成种群中）存在雄性偏扩散的证据，并且在浣熊在环境中遇到蜱的空间尺度上存在年龄偏差。在组成种群的尺度上，我们的分析表明，浣熊遇到的蜱来自有限数量的美洲犬蜱家族群，这可能是由于个体蜱之间的繁殖差异较大。最后，我们发现了一个时间效应的证据，即浣熊在环境中遇到蜱时会形成相关个体的“聚集”。虽然寄生虫种群的遗传结构在小空间尺度上（例如亚种群）的研究越来越多，但我们的数据表明，由于影响宿主个体遇到寄生虫的时间和生物学因素的相互作用，遗传结构可能起源于亚种群以下的尺度。最终，我们的数据表明，寄生虫的遗传结构必须被视为宿主-寄生虫相互作用中空间和时间变化的结果，而这反过来又受到与宿主和寄生虫都有关的人口因素的驱动。
