<b>Varying phylogenetic signal in susceptibility to four bacterial pathogens across species of Drosophilidae</b>

Bacterial host shifts, where bacterial pathogens jump into and establish infection in a new host species, are an important source of emerging infectious diseases. Here, we use four bacterial pathogens to infect a panel of 36 species of fruit fly that shared a common ancestor ~50 million years ago. We found large amounts of variation in susceptibility across host species to these bacterial pathogens. This variation is explained by the host phylogeny to varying degrees, with hosts clustering into clades with distinct levels of susceptibility. However, the magnitude of the effect varies between the four bacterial pathogens. For three out of the four pathogens tested mortality was correlated with bacterial load, suggesting it is a result of bacterial proliferation in the host. This has important implications for our understanding of the emergence of bacterial pathogens, and to date there are few large-scale experimental studies of bacterial host shifts.细菌宿主转移（Bacterial host shifts）指细菌性病原物跳跃至新宿主物种并成功建立感染的过程，是新发传染病的重要源头之一。本研究选用4种细菌性病原物，感染一组共计36个果蝇物种，这些果蝇共享约5000万年前的共同祖先。研究发现，不同宿主物种对这几种细菌性病原物的易感性存在广泛差异；这种差异在不同程度上可由宿主系统发育（host phylogeny）解释，宿主会聚类为具有不同易感性水平的演化支（clades）。不过，这一效应的强度在4种细菌性病原物之间存在差异。在所测试的4种病原物中，有3种的宿主死亡率与细菌载量（bacterial load）呈显著相关，表明致病效应源于病原物在宿主体内的增殖。该研究结果对于我们理解细菌性病原物的新发过程具有重要意义，而迄今为止针对细菌宿主转移的大规模实验研究仍较为匮乏。