Mammals host a wide diversity of parasites. Lice, comprising more than 5,000 species, are one group of ectoparasites whose major lineages have a somewhat patchwork distribution across the major groups of mammals. Here we explored patterns in the diversification of mammalian lice by reconstructing a higher-level phylogeny of these lice, leveraging whole genome sequence reads to assemble single-copy orthologue genes across the genome. The evolutionary tree of lice indicated that three of the major lineages of placental mammal lice had a single common ancestor. Comparisons of this parasite phylogeny with that for their mammalian hosts indicated that the common ancestor of elephants, elephant shrews and hyraxes (that is, Afrotheria) was the ancestral host of this group of lice. Other groups of placental mammals obtained their lice via host-switching out of these Afrotherian ancestors. In addition, reconstructions of the ancestral host group (bird versus mammal) for all parasitic lice supported an avian ancestral host, indicating that the ancestor of Afrotheria acquired these parasites via host-switching from an ancient avian host. These results shed new light on the long-standing question of why the major groups of parasitic lice are not uniformly distributed across mammals and reveal the origins of mammalian lice.

哺乳动物宿主种类繁多的寄生虫。虱子包括 5,000 多个物种，是一组外寄生虫，其主要谱系在哺乳动物的主要群体中有些错综复杂的分布。在这里，我们通过重建这些虱子的更高级别的系统发育，利用全基因组序列读数在整个基因组中组装单拷贝直系同源基因，探索了哺乳动物虱子多样化的模式。虱子的进化树表明，胎盘哺乳动物虱子的三个主要谱系有一个共同的祖先。将这种寄生虫系统发育与其哺乳动物宿主的系统发育进行比较表明，大象、象鼩和蹄兔（即 Afrotheria）的共同祖先是这组虱子的祖先宿主。其他的胎盘哺乳动物群通过宿主转换出这些非洲兽祖先来获得它们的虱子。此外，所有寄生虱子的祖先宿主群（鸟类与哺乳动物）的重建支持鸟类祖先宿主，表明 Afrotheria 的祖先通过从古代鸟类宿主的宿主转换获得这些寄生虫。这些结果为长期存在的问题提供了新的线索，即为什么主要的寄生虱群在哺乳动物中分布不均匀，并揭示了哺乳动物虱子的起源。