Epidemiological, Evolutionary, and Coevolutionary Implications of Context-Dependent Parasitism
Epidemiological, Evolutionary, and Coevolutionary Implications of Context-Dependent Parasitism
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环境相关寄生的流行病学、进化和共同进化意义
作者：
P. Vale;Alastair J. Wilson;A. Best;M. Boots;T. Little
随着寄生虫数量的增加，预计感染受害者将遭受越来越多的痛苦。然而，在某些条件下，生长更快的寄生虫似乎不会造成更大的损害，而且感染是可以容忍的。我们通过评估寄生虫种群增长和宿主健康之间的关系如何对环境变化敏感来研究这些条件。在甲壳类动物大水蚤及其寄生细菌拉莫萨巴氏菌的实验感染中，我们展示了一种相互作用是如何容易地从一种严重的相互作用转变为一种可容忍的关系，即当宿主适应度随着寄生虫生长的每一个单位而大幅下降时，通过改变简单的环境变量：温度和食物供应。我们通过模拟不同感染严重程度下的病原体进化和疾病传播，探讨了这种转变的进化和流行病学意义，并发现促进耐受性的环境变化最终导致种群容纳更多的寄生个体。我们还发现，选择的机会，正如性状周围的差异所表明的那样，随着环境处理而有很大的变化。因此，我们的研究结果提示了共同进化热点和冷点的两种机制：耐受性的空间差异和选择机会的空间差异。
Victims of infection are expected to suffer increasingly as parasite population growth increases. Yet, under some conditions, faster-growing parasites do not appear to cause more damage, and infections can be quite tolerable. We studied these conditions by assessing how the relationship between parasite population growth and host health is sensitive to environmental variation. In experimental infections of the crustacean Daphnia magna and its bacterial parasite Pasteuria ramosa, we show how easily an interaction can shift from a severe interaction, that is, when host fitness declines substantially with each unit of parasite growth, to a tolerable relationship by changing only simple environmental variables: temperature and food availability. We explored the evolutionary and epidemiological implications of such a shift by modeling pathogen evolution and disease spread under different levels of infection severity and found that environmental shifts that promote tolerance ultimately result in populations harboring more parasitized individuals. We also find that the opportunity for selection, as indicated by the variance around traits, varied considerably with the environmental treatment. Thus, our results suggest two mechanisms that could underlie coevolutionary hotspots and coldspots: spatial variation in tolerance and spatial variation in the opportunity for selection.