Lice and Their Bacterial Sidekicks Have Evolved Together for Millions of Years

A Florida Museum of Natural History study provides new insights into the complex, shared history between blood-sucking lice and the vitamin-producing bacterial sidekicks that enable them to parasitize mammals, including primates and humans. The study was published online on April 14, 2017 in Molecular Biology and Evolution. The study is titled “Primates, Lice and Bacteria: Speciation and Genome Evolution in the Symbionts of Hominid Lice.” Lice depend on bacteria to supply essential vitamins missing from blood, their only food source. These bacterial partners live in specialized cells inside their insect hosts and pass from a female louse to her offspring. Lice could not survive without their symbiotic bacteria, and the bacteria, in turn, cannot live outside their insect hosts. When their partnership began, however, and how it has evolved over time have been unclear. Previous studies suggested lice acquired and replaced their bacterial symbionts multiple times over their evolutionary history. But a study by Florida Museum researchers Bret Boyd, Ph.D., and David Reed, Ph.D., found that lice that parasitize primates and humans have hosted their endosymbionts continuously for at least 20 to 25 million years, aligning with the time period during which great apes and old world monkeys shared a common ancestor. As primates evolved, so did lice, and the evolution of their bacterial partners stayed closely in step. The data provide a new perspective on the evolutionary tree of these symbiotic bacteria, said Dr. Boyd, who conducted the research as a doctoral student at the museum. "While lice are highly maligned, they provide a wealth of scientific information," said Dr. Boyd, now a postdoctoral researcher at the University of Georgia and the study's first author.
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