Reconstructing the Evolutionary History of Bacterial Endosymbiosis in Obligate Blood-feeding Lice (Phthiraptera: Anoplura)

这个项目将开始深入探索共同生活了数百万年的三种生物，哺乳动物，它们的寄生虱子，以及生活在虱子内的细菌。这些虱子靠吸食宿主的血液生存，然而哺乳动物的血液缺乏寄生虱子生存所需的营养。为了完成它们的生命周期，虱子还必须从虱子体内作为共生体生活的细菌中获得营养。以前人们认为，很久以前获得了一种细菌共生体，使这些虱子能够单独依靠哺乳动物的血液生存。然而，PI， co -PI和合作者的初步工作表明，每个主要的虱子群体都有自己的内共生体，与其他群体明显不同。这表明虱子已经与内部共生体发生过几次，这就提出了一个问题：哺乳动物、虱子和细菌之间这种复杂的三级相互作用发生的频率是多少？研究人员将使用哺乳动物、虱子和细菌的DNA序列来精确研究这些群体在过去8000万年中是如何共同进化的。由于许多被研究的哺乳动物都有很好的化石记录，研究人员将能够校准它们的进化树，以估计每种哺乳动物/虱子/细菌关联的年龄。正在研究的虱子包括人类的寄生虫，如人类头虱和人类衣服虱。头虱在发达国家很流行，因为虱子已经对用于治疗人类的杀虫洗发水产生了抗药性。衣虱不太常见，它们引发的三种致命疾病仍然威胁着欠发达国家的人类。了解虱子如何与它们的哺乳动物宿主及其细菌共生体相互作用，对于治疗人类虱子侵扰非常重要。该项目将培养1名博士后、1名博士生和数名本科生，研究方向为分子和形态系统发育学（构建进化树）以及共同系统发育学（研究共同进化的生物体）。它还将利用参与的自然历史博物馆现有的基础设施，开发一个利用哺乳动物、虱子和细菌来教授进化生物学基本原理的项目。

This project will begin an in-depth exploration of three types of organisms that have lived together for many millions of years, mammals, their parasitic lice, and bacteria that live within the lice. These lice survive by taking blood meals from their host, yet mammalian blood is lacking nutrients that are required for the survival of the parasitic lice. In order to complete their life cycle the lice must also get nourishment from bacteria that live as symbionts within the lice. It was previously thought that the acquisition of a single bacterial symbiont long ago enabled these lice to persist on mammal blood alone. However, preliminary work by the PI, Co-PIs, and collaborators has shown that each major group of lice has its own endosymbiont distinctly different from the others. This suggests that lice have taken on internal symbionts several times, raising the question how often have these complex three-level interactions arisen between mammals, lice, and bacteria? The investigators will use DNA sequences from mammals, lice, and bacteria to study precisely how these groups have been evolving together over the last 80 million years. Because many of the mammals being studied have good fossil records, the investigators will be able to calibrate their evolutionary trees in order to estimate the age of each mammal/louse/bacterium association. The lice being studied include parasites of humans such as the human head louse and the human clothing louse. Head lice are epidemic in developed countries because lice have evolved resistance to the insecticidal shampoos used to treat people. Clothing lice, which are less common, cause three deadly diseases that still threaten humans in underdeveloped countries. Understanding how lice interact with their mammalian hosts and their bacterial symbionts is important for treating human louse infestations. This project will train one postdoc, one PhD student, and several undergraduate students in molecular and morphological phylogenetics (building evolutionary trees) as well as cophylogenetics (the study of co-evolving organisms). It will also take advantage of the infrastructure available at participating natural history museums to develop a program using mammals, lice, and bacteria to teach basic principles of evolutionary biology.