Environmental variation mediates the prevalence and co-occurrence of parasites in the common lizard, Zootoca vivipara
Environmental variation mediates the prevalence and co-occurrence of parasites in the common lizard, Zootoca vivipara
复制标题
环境变化介导普通蜥蜴胎生动物寄生虫的流行和共存
作者：
Qiangsheng Wu;M. Richard;A. Rutschmann;D. Miles;J. Clobert
研究背景昆虫及其寄生物处于相互选择中，导致协同进化。然而，寄生虫不仅依赖于宿主，还依赖于宿主的环境。此外，单个宿主物种很少被单个物种的寄生虫侵染，并且通常支持多个物种（即，多侵染）。虽然寄生虫和其宿主之间的军备竞赛已经得到了很好的研究，但关于环境条件如何影响导致多重感染的过程的数据很少。在这项研究中，我们检查是否：（1）环境因素包括海拔、温度、植被覆盖、人为干扰和牲畜放牧等影响螨和蜱两种体外寄生虫在宿主身上的流行（2）螨类与蜱类之间存在明显的竞争关系。但随着人类干扰和牲畜的存在而减少。相反，蜱虫侵染的概率与相同的因素呈负相关。个体低身体状况和男性有较高的螨负荷。然而，对于蜱虫负荷，这种模式并不明显。结构方程模型的结果表明，螨和蜱间接和负面影响对方的侵扰概率，通过涉及环境背景的相互作用。我们检测到螨和蜱之间的直接负相关，只有当考虑估计寄生虫负荷。这表明，螨和蜱都可以附着在同一主机，但一旦他们开始积累，只有其中之一需要advantage.ConclusionThe宿主的环境有很强的影响螨和蜱的侵染概率和寄生虫负荷。螨和蜱之间的Autecological差异，由他们的相反的模式沿着环境梯度，可以解释弱当代种间竞争的模式。我们的研究结果强调了在宿主-寄生虫共同进化研究中包括环境因素和每个寄生虫物种的自然历史的重要性。
BackgroundHosts and their parasites are under reciprocal selection, leading to coevolution. However, parasites depend not only on a host, but also on the host’s environment. In addition, a single host species is rarely infested by a single species of parasite and often supports multiple species (i.e., multi-infestation). Although the arms race between a parasite and its host has been well studied, few data are available on how environmental conditions may influence the process leading to multiple infestations. In this study, we examine whether: (1) environmental factors including altitude, temperature, vegetation cover, human disturbance, and grazing by livestock affect the prevalence of two types of ectoparasites, mites and ticks, on their host (the common lizard, Zootoca vivipara) and (2) competition is evident between mites and ticks.ResultsWe found the probability of mite infestation increased with altitude and vegetation cover, but decreased with human disturbance and presence of livestock. In contrast, the probability of tick infestation was inversely associated with the same factors. Individuals with low body condition and males had higher mite loads. However, this pattern was not evident for tick loads. The results from a structural equation model revealed that mites and ticks indirectly and negatively affected each other’s infestation probability through an interaction involving the environmental context. We detected a direct negative association between mites and ticks only when considering estimates of parasite load. This suggests that both mites and ticks could attach to the same host, but once they start to accumulate, only one of them takes advantage.ConclusionThe environment of hosts has a strong effect on infestation probabilities and parasite loads of mites and ticks. Autecological differences between mites and ticks, as indicated by their opposing patterns along environmental gradients, may explain the pattern of weak contemporary interspecific competition. Our findings emphasize the importance of including environmental factors and the natural history of each parasite species in studies of host–parasite coevolution.