Data from: 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 via bacteriocins, the faster killing isolate had a competitive advantage. Alternatively, nematodes could gain a competitive advantage when they carried bacteria able to inhibit the bacteria of their competitor. Thus, the combination of nematode/bacterial traits that led to competitive success depended on which isolates were paired, suggesting that variation in competitive interactions may be important for maintaining species diversity in this community.

共感染（coinfection）施加的选择压力可能因寄生生物间的宿主内竞争（within-host competition）机制而异。掠夺性竞争（exploitative competition）理论上会青睐毒性更强的寄生生物，而干扰性竞争（interference competition）则可能导致更低的毒力。本研究旨在探究掠夺性竞争还是干扰性竞争决定了两种斯氏线虫属（Steinernema spp.）物种间的竞争结局——这类线虫与其共生的发光杆菌属（Xenorhabdus spp.）细菌共同感染并杀死昆虫宿主。我们对每个线虫物种的多个分离株（isolate）——均携带其自然共生的细菌——开展了两项表征：其一为其杀死昆虫宿主的速率，其二为其细菌通过被称为‘细菌素（bacteriocins）’的杀菌毒素干扰其他细菌生长的能力。研究发现，在双株竞争实验中，预测哪个物种具有竞争优势时，掠夺性能力与干扰性能力均发挥了关键作用。当线虫所携带的细菌无法通过细菌素产生相互作用时，致死速度更快的分离株将获得竞争优势；反之，若线虫携带的细菌能够抑制竞争者的细菌，则该线虫可获得竞争优势。由此可见，决定竞争成功的线虫与细菌性状组合取决于所配对的分离株类型，这表明竞争相互作用的变异或许对维持该群落的物种多样性至关重要。