# Host and Microbe Scale Processes Jointly Shape Spatial Variation in Aphaenogaster (Hymenoptera: Formicidae)associated Wolbachia

## TL;DR

This paper explores how both host and microbe-level factors influence the spatial distribution of Wolbachia in ants, showing that these factors are intertwined and complicate understanding their spread.

## Contribution

The study introduces a novel approach to disentangle host- and microbe-scale processes shaping Wolbachia distribution in ants.

## Key findings

- Wolbachia abundance varies spatially at both host and microbe scales in Aphaenogaster ants.
- Host- and microbe-scale environmental selection are correlated, complicating isolation of their individual effects.
- Using co-occurrence of host lineages helps assess the joint influence of host and microbe-scale processes.

## Abstract

The spatial distributions of host-associated (HA) microbes are shaped by the spatial processes of environmental selection and dispersal. However, unlike free-living organisms, HA microbes experience selection and dispersal at two separate spatial scales – the scale of the microbes and the scale of their hosts. Therefore, HA microbes must tolerate both the environment created by their host (microbe-scale environment) and the environment in which their host resides (host-scale environment). Likewise, HA microbes can disperse both between hosts through horizontal or vertical transmission (microbe-scale dispersal) and between locations through host movement (host-scale dispersal). In this paper, we examine how host- and microbe-scale spatial processes contribute to the spatial distribution of Wolbachia endosymbionts in Aphaenogaster fulva-rudis-texana (Hymenoptera: Formicidae) complex ants from Great Smoky Mountains National Park. We begin by identifying significant spatial variation in Wolbachia relative abundance at both the host (across the landscape) and microbe (across host lineages) scales. We then demonstrate a correlation between host- and microbe-scale environmental selection, complicating efforts to isolate the independent effects of host- versus microbe-scale processes. To overcome this challenge, we leverage both the broad distributions of individual host lineages across different environments and sites of co-occurrence between different host lineages within the same environments. This allows us to assess how both host- and microbe-scale processes contribute to spatial variation in our system. Ultimately, our results shed light on the myriad of interacting factors governing spatial variation in HA microbes and why spatial variation in HA microbes is more challenging to understand than spatial variation in free-living organisms.