Centre for Ecology, Evolution and Conservation, School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich, Norfolk, UK.
Oecologia. 2012 Mar;168(3):691-701. doi: 10.1007/s00442-011-2149-z. Epub 2011 Oct 9.
Pathogens can exert strong selective forces upon host populations. However, before we can make any predictions about the consequences of pathogen-mediated selection, we first need to determine whether patterns of pathogen distribution are consistent over spatiotemporal scales. We used molecular techniques to screen for a variety of blood pathogens (avian malaria, pox and trypanosomes) over a three-year time period across 13 island populations of the Berthelot's pipit (Anthus berthelotii). This species has only recently dispersed across its range in the North Atlantic, with little subsequent migration, providing an ideal opportunity to examine the causes and effects of pathogenic infection in populations in the early stages of differentiation. We screened 832 individuals, and identified two strains of Plasmodium, four strains of Leucocytozoon, and one pox strain. We found strong differences in pathogen prevalence across populations, ranging from 0 to 65%, and while some fluctuations in prevalence occurred, these differences were largely stable over the time period studied. Smaller, more isolated islands harboured fewer pathogen strains than larger, less isolated islands, indicating that at the population level, colonization and extinction play an important role in determining pathogen distribution. Individual-level analyses confirmed the island effect, and also revealed a positive association between Plasmodium and pox infection, which could have arisen due to dual transmission of the pathogens by the same vectors, or because one pathogen lowers resistance to the other. Our findings, combined with an effect of infection on host body condition, suggest that Berthelot's pipits are subject to different levels of pathogen-mediated selection both across and within populations, and that these selective pressures are consistent over time.
病原体可以对宿主种群施加强大的选择压力。然而，在我们能够对病原体介导的选择的后果做出任何预测之前，我们首先需要确定病原体的分布模式是否在时空尺度上保持一致。我们使用分子技术，在三年内对分布于北大西洋的 13 个贝氏雀（Anthus berthelotii）岛屿种群中的各种血液病原体（禽疟原虫、痘病毒和锥虫）进行了筛选。这种物种在最近才在其分布范围内扩散，随后迁徙较少，为研究在种群分化的早期阶段感染致病性病原体的原因和影响提供了理想的机会。我们对 832 只个体进行了筛选，鉴定出了两种疟原虫株、四种白细胞虫株和一种痘病毒株。我们发现病原体的流行率在种群之间存在很大差异，从 0%到 65%不等，虽然流行率存在一些波动，但这些差异在研究期间基本保持稳定。较小、较孤立的岛屿比较大、较不孤立的岛屿携带的病原体株较少，这表明在种群水平上，定殖和灭绝在决定病原体分布方面起着重要作用。个体水平的分析证实了岛屿效应，并且还揭示了疟原虫和痘病毒感染之间存在正相关关系，这可能是由于同一媒介同时传播两种病原体，或者是由于一种病原体降低了对另一种病原体的抵抗力。我们的研究结果表明，贝氏雀受到来自病原体的不同程度的选择压力，无论是在种群之间还是在种群内部，并且这些选择压力是随着时间的推移而保持一致的。此外，感染对宿主身体状况的影响也表明，贝氏雀正受到不同程度的病原体介导的选择压力。
