Tick Microbiomes in Neotropical Forest Fragments Are Best Explained by Tick-Associated and Environmental Factors Rather than Host Blood Source

Abstract

The composition of tick microbiomes varies both within and among tick species. Whether this variation is intrinsic (related to tick characteristics) or extrinsic (related to vertebrate host and habitat) is poorly understood but important, as microbiota can influence the reproductive success and vector competence of ticks. We aimed to uncover what intrinsic and extrinsic factors best explain the microbial composition and taxon richness of 11 species of neotropical ticks collected from eight species of small mammals in 18 forest fragments across central Panama. Microbial richness varied among tick species, life stages, and collection sites but was not related to host blood source. Microbiome composition was best explained by tick life stage, with bacterial assemblages of larvae being a subset of those of nymphs. Collection site explained most of the bacterial taxa with differential abundance across intrinsic and extrinsic factors. Francisella and Rickettsia were highly prevalent, but their proportional abundance differed greatly among tick species, and we found both positive and negative cooccurrence between members of these two genera. Other tick endosymbionts (e.g., Coxiella and Rickettsiella) were associated with specific tick species. In addition, we detected Anaplasma and Bartonella in several tick species. Our results indicate that the microbial composition and richness of neotropical ticks are principally related to intrinsic factors (tick species and life stage) and collection site. Taken together, our analysis informs how tick microbiomes are structured and can help anchor our understanding of tick microbiomes from tropical environments more broadly.IMPORTANCE Blood-feeding arthropod microbiomes often play important roles in disease transmission, yet the factors that structure tick microbial communities in the Neotropics are unknown. Utilizing ticks collected from live animals in neotropical forest fragments, this study teases apart the contributions of intrinsic and extrinsic tick-associated factors on tick microbial composition as well as which specific microbes contribute to differences across tick species, tick life stages, the mammals they fed on, and the locations from where they were sampled. Furthermore, this study provides revelations of how notable tick-associated bacterial genera are interacting with other tick-associated microbes as well as the forest animals they encounter.

Keywords: Lyme disease; Panama; Rickettsia; anaplasma; endosymbionts; environmental microbiology; microbiome; neotropical; tick; tick-borne pathogens.

FIG 1

Map of Central Panama showing the locations of the 18 forest fragments that were sampled. Site codes correspond to sample numbers described in Table 1.

FIG 2

Proportional abundance of amplicon sequence variants (ASVs) in the microbiome of ticks collected from small mammals in forests across Central Panama compared between tick life stages, tick species, host orders, and collection sites. ASVs with an average relative abundance of >20% of total sequences are displayed individually, and the remainder are grouped under Other (red).

FIG 3

Number of differentially abundant microbial taxa as uncovered by ANCOM, summarized for tick species, life stage, host order, and collection site. Only four microbes are differentially abundant in all four metadata categories.

FIG 4

Proportional abundance of notable bacterial genera that include tick endosymbionts and pathogens (i.e., Anaplasma, Coxiella, Francisella, Rickettsia, and Rickettsiella), compared between tick life stages, tick species, host orders, and collection sites. Bacterial taxa that do not match these genera are assigned as Other and are shown in gray.

FIG 5

Bipartite network of notable ASVs (Anaplasma, Bartonella, Coxiella, Francisella, Rickettsia, and Rickettsiella) and the tick species in which they were detected, separated by the host (rodent or opossum) from which these ticks were collected. The width of the bars is proportional to the number of individuals sampled per tick species (lower black bars) and the total number of ticks in which each ASV was detected (upper black bars). The width of the gray links connecting the ticks and bacterial ASVs is proportional to the number of ticks of a specific species in which an ASV was detected.

FIG 6

Network of bacterial cooccurrences within tick nymphs and larvae for all bacterial ASVs found in ticks (n = 733) from all sites. Circular nodes represent bacterial ASVs with significant correlation with other ASVs in the network. Red lines indicate negative correlations, whereas blue lines indicate positive correlations between two ASVs.