Department of Ecology and Evolutionary Biology, Yale University, New Haven, Connecticut 06520, USA.
Evolution. 2010 Nov;64(11):3273-86. doi: 10.1111/j.1558-5646.2010.01051.x.
Understanding how evolution promotes pathogen emergence would aid disease management, and prediction of future host shifts. Increased pathogen infectiousness of different hosts may occur through direct selection, or fortuitously via indirect selection. However, it is unclear which type of selection tends to produce host breadth promoting pathogen emergence. We predicted that direct selection for host breadth should foster emergence by causing higher population growth on new hosts, lower among-population variance in growth on new hosts, and lower population variance in growth across new hosts. We tested the predictions using experimentally evolved vesicular stomatitis virus populations, containing groups of host-use specialists, directly selected generalists, and indirectly selected generalists. In novel-host challenges, viruses directly selected for generalism showed relatively higher or equivalent host growth, lower among-population variance in host growth, and lower population variance in growth across hosts. Thus, two of three outcomes supported our prediction that directly selected host breadth should favor host colonization. Also, we observed that indirectly selected generalists were advantaged over specialist viruses, indicating that fortuitous changes in host breadth may also promote emergence. We discuss evolution of phenotypic plasticity versus environmental robustness in viruses, virus avoidance of extinction, and surveillance of pathogen niche breadth to predict future likelihood of emergence.
了解进化如何促进病原体的出现将有助于疾病的管理和未来宿主转移的预测。不同宿主的病原体传染性的增加可能是通过直接选择，或者偶然通过间接选择发生的。然而，目前还不清楚哪种类型的选择更容易产生促进病原体出现的宿主广度。我们预测，直接选择宿主广度应该会促进病原体的出现，因为它会导致在新宿主上更高的种群增长率、在新宿主上的种群增长率的更低的种群间变异性，以及在新宿主上的种群增长率的更低的种群间变异性。我们使用实验进化的水疱性口炎病毒种群来检验这些预测，这些病毒种群包含宿主使用专家群体、直接选择的广宿主适应者群体和间接选择的广宿主适应者群体。在新宿主的挑战中，直接选择的广宿主适应者表现出相对较高或同等的宿主增长率、较低的种群间宿主增长率的变异性以及较低的宿主间种群增长率的变异性。因此，三个结果中的两个支持了我们的预测，即直接选择的宿主广度应该有利于宿主的定植。此外，我们观察到间接选择的广宿主适应者比宿主使用专家病毒具有优势，这表明宿主广度的偶然变化也可能促进病原体的出现。我们讨论了病毒中表型可塑性与环境稳健性的进化、病毒避免灭绝的能力，以及监测病原体生态位广度以预测未来出现的可能性。
