The scale affects our view on the identification and distribution of microbial communities in ticks

Abstract

Ticks transmit the highest variety of pathogens impacting human and animal health worldwide. It is now well established that ticks also harbour a microbial complex of coexisting symbionts, commensals and pathogens. With the development of high throughput sequencing technologies, studies dealing with such diverse bacterial composition in tick considerably increased in the past years and revealed an unexpected microbial diversity. These data on diversity and composition of the tick microbes are increasingly available, giving crucial details on microbial communities in ticks and improving our knowledge on the tick microbial community. However, consensus is currently lacking as to which scales (tick organs, individual specimens or species, communities of ticks, populations adapted to particular environmental conditions, spatial and temporal scales) best facilitate characterizing microbial community composition of ticks and understanding the diverse relationships among tick-borne bacteria. Temporal or spatial scales have a clear influence on how we conduct ecological studies, interpret results, and understand interactions between organisms that build the microbiome. We consider that patterns apparent at one scale can collapse into noise when viewed from other scales, indicating that processes shaping tick microbiome have a continuum of variability that has not yet been captured. Based on available reports, this review demonstrates how much the concept of scale is crucial to be considered in tick microbial community studies to improve our knowledge on tick microbe ecology and pathogen/microbiota interactions.

Keywords: Scales; Spatial; Temporal; Tick microbe interactions; Tick microbiome.

Fig. 1

Improving our understanding of the tick microbial community ecology. Spatial and temporal studies ranging in scale from that of tick organs to population have allowed us detect patterns of distribution to finally develop predictive models on pathogen/microbiota interactions. Pictures: organs (Ladislav Simo), genera and species (CDC), populations (Philippe Garo, Agence Phanie)

Fig. 2

The time scale may affect the composition of tick microbiome. The illustration schematically represents the seasonal and inter-year variations of a hypothetical population of ticks. The different stages of a tick species have different inter-year densities and a variable seasonality in the same territory that is mainly caused by climate factors. The three stages of the tick may coexist at the same time and at the same habitat patch, and their dynamics (as lines in the figure) may differ from year to year. According to the moment of the year and the host availability, ticks can exploit different species of hosts, resulting in an “exchange” of bacteria obtained from blood meal that may be incorporated into the gut microbiome of the ticks. While immature stages may feed on small vertebrates, large ungulates can also support large numbers of immatures and adults. This adds variability to the microbiome because the seasonality is different each year. Climate shapes these patterns and host availability is different at different moments of the year. The X-axis represents three years and the Y-axis indicates tick density (hypothetical values). Silhouettes of vertebrates and ticks are merely illustrative and do not represent a specific vertebrate or tick stage

Fig. 3

The spatial scale as driver of variability in the tick microbiome. a The connectivity patterns of the landscape drive the presence/absence of some key hosts and exchange of animals among patches, shaping a variable host composition in each patch. Some patches may be highly connected (wide arrows) while others are poorly connected, blocking the movements of vertebrates. This adds a spatial component to the composition and the variability of the tick microbiome. b The vegetal composition of the habitat may differ and modulate the microclimate, shaping tick density. The figure intends to show a gradient of biomes, in which hosts may be abundant or scarce, or even absent. Ticks also have different survival and questing rates at the small scale of the habitat patch. Such intra-patch spatial diversity shapes an extra variability of the tick microbiome