Data from: The evolution of reduced antagonism – a role for host-parasite coevolution

Why do some host-parasite interactions become less antagonistic over evolutionary time? Vertical transmission can select for reduced antagonism. Vertical transmission also promotes coevolution between hosts and parasites. Therefore, we hypothesized that coevolution itself may underlie transitions to reduced antagonism. To test the coevolution hypothesis, we selected for reduced antagonism between the host Caenorhabditis elegans and its parasite Serratia marcescens. This parasite is horizontally transmitted, which allowed us to study coevolution independently of vertical transmission. After 20 generations, we observed a response to selection when coevolution was possible: reduced antagonism evolved in the co-passaged treatment. Reduced antagonism, however, did not evolve when hosts or parasites were independently selected, without coevolution. In addition, we found strong local adaptation for reduced antagonism between replicate host/parasite lines in the co-passaged treatment. Taken together, these results strongly suggest that coevolution was critical to the rapid evolution of reduced antagonism.为何部分宿主-寄生虫互作会在演化过程中逐渐降低拮抗性？垂直传播可通过选择压力降低拮抗性，同时还能推动宿主与寄生虫间的协同演化（coevolution）。据此，我们提出假说：协同演化本身或许是拮抗性降低这一演化转变的核心驱动因素。为验证这一协同演化假说，我们针对宿主秀丽隐杆线虫（Caenorhabditis elegans）与其寄生虫粘质沙雷氏菌（Serratia marcescens）之间的拮抗性降低进行了选择实验。该寄生虫为水平传播，这使得我们能够脱离垂直传播的干扰，独立开展协同演化研究。历经20代后，我们观察到：当允许发生协同演化时，选择实验产生了预期响应——共传代处理组中演化出了拮抗性降低的表型。然而，当宿主或寄生虫被单独选择、不存在协同演化的情况下，并未出现拮抗性降低的演化现象。此外，我们在共传代处理组的重复宿主-寄生虫品系间，发现了拮抗性降低相关的显著局部适应信号。综上，上述结果强有力地表明，协同演化是拮抗性快速降低这一演化过程的关键驱动因素。