Pathogens continue to emerge from increased contact with novel host species. Whilst these hosts can represent distinct environments for pathogens, the impacts of host genetic background on how a pathogen evolves post-emergence are unclear. In a novel interaction, we experimentally evolved a pathogen (Staphylococcus aureus) in populations of wild nematodes (Caenorhabditis elegans) to test whether host genotype and genetic diversity affect pathogen evolution. After ten rounds of selection, we found that pathogen virulence evolved to vary across host genotypes, with differences in host metal ion acquisition detected as a possible driver of increased host exploitation. Diverse host populations selected for the highest levels of pathogen virulence, but infectivity was constrained, unlike in host monocultures. We hypothesise that population heterogeneity might pool together individuals that contribute disproportionately to the spread of infection or to enhanced virulence. The genomes of evolved populations were sequenced, and it was revealed that pathogens selected in distantly-related host genotypes diverged more than those in closely-related host genotypes. S. aureus nevertheless maintained a broad host range. Our study provides unique empirical insight into the evolutionary dynamics that could occur in other novel infections of wildlife and humans.

由于与新宿主物种的接触增加，病原体不断出现。虽然这些宿主可以代表病原体的不同环境，但宿主遗传背景对病原体在出现后如何进化的影响尚不清楚。在一种新颖的相互作用中，我们通过实验在野生线虫（秀丽隐杆线虫）种群中进化出一种病原体（金黄色葡萄球菌）) 来测试宿主基因型和遗传多样性是否影响病原体进化。经过十轮选择后，我们发现病原体毒力在宿主基因型之间发生变化，宿主金属离子获取的差异被检测为宿主利用增加的可能驱动因素。选择不同的宿主群体以获得最高水平的病原体毒力，但传染性受到限制，这与宿主单一培养物不同。我们假设种群异质性可能会将对感染传播或毒力增强贡献不成比例的个体聚集在一起。对进化种群的基因组进行了测序，发现在远缘相关宿主基因型中选择的病原体比在密切相关宿主基因型中选择的病原体差异更大。金黄色葡萄球菌尽管如此，仍保持广泛的宿主范围。我们的研究为野生动物和人类的其他新型感染中可能发生的进化动力学提供了独特的经验见解。