Alternative paths to success in a parasite community: within-host competition can favor higher virulence or direct interference

Selection imposed by coinfection may vary with the mechanism of within-host competition between parasites. Exploitative competition is predicted to favor more virulent parasites, while interference competition may result in lower virulence. Here, we examine whether exploitative or interference competition determines the outcome of competition between two nematode species (Steinernema spp.), which in combination with their bacterial symbionts (Xenorhabdus spp.), infect and kill insect hosts. Multiple isolates of each nematode species, carrying their naturally associated bacteria, were characterized by (1) the rate at which they killed insect hosts, and by (2) the ability of their bacteria to interfere with each other’s growth via bacteriocidal toxins called \"bacteriocins.\" We found that both exploitative and interference abilities were important in predicting which species had a selective advantage in pairwise competition experiments. When nematodes carried bacteria that did not interact...

共感染所施加的选择压力，可因寄生虫间宿主内竞争的机制差异而有所不同。理论预测，利用性竞争（exploitative competition）会青睐致病力更强的寄生虫，而干扰性竞争（interference competition）则可能导致寄生虫致病力降低。本研究旨在探究：在两种斯氏线虫属（Steinernema spp.）线虫与其共生细菌——致病杆菌属（Xenorhabdus spp.）共同感染并致死昆虫宿主的体系中，究竟是利用性竞争还是干扰性竞争决定了二者的竞争结局。我们对每种线虫的多个天然携带共生菌的分离株开展了两项特征表征：其一为其致死昆虫宿主的速率，其二为其共生细菌通过被称为“细菌素（bacteriocins）”的杀菌毒素干扰其他细菌生长的能力。研究发现，在两两竞争实验中，利用性竞争与干扰性竞争能力均是预测哪种线虫物种可获得选择优势的关键因素。当线虫所携带的细菌不存在相互作用时……