Lyme disease, a zoonotic disease, is the most prevalent vector-borne disease in the Northern Hemisphere, and is vectored by Ixodes species ticks. Vector-borne pathogens are increasingly found to interact with the vector’s microbiome, influencing disease transmission dynamics. Diversity of the vector (tick) microbiome can impact pathogen transmission, yet the biotic and abiotic factors that drive microbiome diversity are largely unresolved, especially under natural, field conditions. Furthermore, the processes that regulate the formation and development of the microbiome are largely unresolved. While obligate endosymbionts are vertically transmitted in ticks, it is not known how much of the tick microbiome is acquired through vertical transmission versus horizontally from the environment or interactions with blood meal sources. Using next-generation 16s rRNA sequencing, we examined the microbiome of Ixodes pacificus, the vector of Lyme disease in the western US, across life stages, infection status, host blood meal, and environment.
We found a decrease in both species richness and evenness as the tick matures from larva to adult. However, there is no significant difference between naturally-infected nymphs and uninfected nymphs. There is also a strong impact of host blood meal identity on tick microbiome species richness and composition. Western fence lizards, a host that is refractory to the Lyme disease pathogen, significantly reduces microbial species richness and evenness in ticks relative to ticks that feed on a mammalian reservoir host. Furthermore, lab-reared nymph microbiome diversity was found be compositionally distinct and significantly depauperate relative to field-collected nymphs. These results highlight unique patterns in the microbial community of I. pacificus that is distinct from other tick species. We provide strong evidence that ticks acquire a significant portion of their microbiome through exposure to their environment despite a loss of overall diversity through life stages, perhaps due to elimination of microbial diversity with blood meal feeding. Furthermore, host blood meal-driven reduction of tick microbiome diversity may have lifelong repercussions on I. pacificus vector competency and ultimately disease ecology dynamics.