Maladies Infectieuses et Vecteurs: Ecologie, Génétique, Evolution et Contrôle, UMR UM1 UM2 CNRS 5290 - UR IRD 224, Centre IRD, 911 Avenue Agropolis, BP 64501, 34394, Montpellier, France.
Mol Ecol. 2014 Jul;23(13):3292-305. doi: 10.1111/mec.12815. Epub 2014 Jun 19.
Historical patterns of dispersal and population isolation are key components shaping contemporary genetic diversity across landscapes and require explicit consideration when examining the relative role of different factors in driving the evolution of host specificity in parasitic organisms. In this study, we investigate the worldwide colonization history of a common ectoparasite of seabirds, the tick Ixodes uriae. This tick has a circumpolar distribution across both hemispheres but has repeatedly formed host-specific races within different regions. By combining mitochondrial and nuclear data, we infer how this species spread to its present-day distribution and how the colonization process may have affected the geographic and host-associated structure of this tick within regions. We demonstrate that I. uriae is highly structured at a global scale and isolates into four genetic groups that correspond to well-defined geographical regions. Molecular dating suggests that the diversification of I. uriae began in the early Miocene (22 Myr) and that this tick colonized most of the southern hemisphere before moving into northern latitudes via two independent routes. However, no relationship between the degree of host race divergence and colonization history was evident, supporting previous hypotheses that host specialization evolves relatively rapidly in this parasite, but does not typically lead to speciation. We discuss the possible historical and contemporary mechanisms of large-scale dispersal for this ectoparasite and how its biological characteristics may condition current patterns of genetic diversity. More generally, our results illustrate how combining broad-scale sampling and modern molecular tools can help disentangle complex patterns of diversification in widespread parasites.
历史上的扩散模式和种群隔离是塑造景观中当代遗传多样性的关键组成部分，在研究不同因素在驱动寄生生物宿主特异性进化中的相对作用时，需要明确考虑这些因素。在这项研究中，我们调查了海鸟体外寄生虫壁虱的全球殖民历史。这种壁虱在两个半球的极地都有分布，但在不同地区多次形成了具有宿主特异性的种族。通过结合线粒体和核数据，我们推断了该物种如何传播到其现今的分布，并探讨了这一殖民过程如何影响该种壁虱在区域内的地理和宿主相关结构。我们证明，I. uriae 在全球范围内高度结构，分为四个与明确界定的地理区域相对应的遗传群体。分子年代学表明，I. uriae 的多样化始于中新世早期（2200 万年前），在此之后，该壁虱通过两条独立的路线从南半球的大部分地区向北方纬度移动。然而，在宿主种族分化程度和殖民历史之间没有明显的关系，这支持了先前的假设，即在这种寄生虫中，宿主特化相对较快地进化，但通常不会导致物种形成。我们讨论了这种外寄生虫进行大规模扩散的可能的历史和当代机制，以及其生物学特征如何影响当前的遗传多样性模式。更普遍地说，我们的结果说明了如何结合广泛的采样和现代分子工具来帮助理清广泛分布的寄生虫中复杂的多样化模式。
