Gibson Amanda K, Baffoe-Bonnie Helena, Penley McKenna J, Lin Julie, Owens Raythe, Khalid Arooj, Morran Levi T
Department of Biology, Emory University, Atlanta, GA, USA.
Department of Biology, University of Virginia, Charlottesville, VA, USA.
J Evol Biol. 2020 Jun;33(6):773-782. doi: 10.1111/jeb.13608. Epub 2020 Mar 9.
Theory on the evolution of niche width argues that resource heterogeneity selects for niche breadth. For parasites, this theory predicts that parasite populations will evolve, or maintain, broader host ranges when selected in genetically diverse host populations relative to homogeneous host populations. To test this prediction, we selected the bacterial parasite Serratia marcescens to kill Caenorhabditis elegans in populations that were genetically heterogeneous (50% mix of two experimental genotypes) or homogeneous (100% of either genotype). After 20 rounds of selection, we compared the host range of selected parasites by measuring parasite fitness (i.e. virulence, the selected fitness trait) on the two focal host genotypes and on a novel host genotype. As predicted, heterogeneous host populations selected for parasites with a broader host range: these parasite populations gained or maintained virulence on all host genotypes. This result contrasted with selection in homogeneous populations of one host genotype. Here, host range contracted, with parasite populations gaining virulence on the focal host genotype and losing virulence on the novel host genotype. This pattern was not, however, repeated with selection in homogeneous populations of the second host genotype: these parasite populations did not gain virulence on the focal host genotype, nor did they lose virulence on the novel host genotype. Our results indicate that host heterogeneity can maintain broader host ranges in parasite populations. Individual host genotypes, however, vary in the degree to which they select for specialization in parasite populations.
生态位宽度进化理论认为，资源异质性会选择更宽的生态位广度。对于寄生虫而言，该理论预测，相对于同质宿主种群，当在基因多样化的宿主种群中进行选择时，寄生虫种群将进化或维持更广泛的宿主范围。为了验证这一预测，我们选择了细菌寄生虫粘质沙雷氏菌，在基因异质（两种实验基因型各占50%混合）或同质（单一基因型占100%）的秀丽隐杆线虫种群中进行杀灭实验。经过20轮选择后，我们通过测量选定寄生虫在两种目标宿主基因型以及一种新宿主基因型上的适应性（即毒力，选定的适应性特征），来比较选定寄生虫的宿主范围。正如预测的那样，异质宿主种群选择出了宿主范围更广的寄生虫：这些寄生虫种群在所有宿主基因型上都获得或维持了毒力。这一结果与在单一宿主基因型的同质种群中的选择情况形成对比。在单一宿主基因型的同质种群中，宿主范围缩小，寄生虫种群在目标宿主基因型上获得毒力，而在新宿主基因型上失去毒力。然而，在第二种宿主基因型的同质种群中进行选择时，这种模式并未重复出现：这些寄生虫种群在目标宿主基因型上没有获得毒力，在新宿主基因型上也没有失去毒力。我们的结果表明，宿主异质性可以使寄生虫种群维持更广泛的宿主范围。然而，单个宿主基因型在选择寄生虫种群专业化程度方面存在差异。
