Host and Microbe Scale Processes Shape Spatial Variation in Aphaenogaster (Hymenoptera: Formicidae) Genetics and Their Microbiota.

Like all ecological communities, host-associated (HA) microbiota are shaped by environmental selection and dispersal limitation. However, unlike communities of free-living organisms, communities of HA microbes experience selection and dispersal at two separate scales - the scale of the microbes and the scale of their hosts. Thus, HA microbes must tolerate not only the environment created by their host (microbe-scale environment), but also, the environment in which their host resides (host-scale environment). Likewise, HA microbes can disperse between hosts through either horizontal or vertical transmission (microbe-scale dispersal) but can also disperse between locations through host movement (host-scale dispersal). In this paper, we examine how multiscale environmental selection and dispersal limitation shape the genetics and HA microbiota of ants in the Aphaenogaster fulva-rudis-texana (Hymenoptera: Formicidae) complex. We begin by showing how spatial variation in Aphaenogaster genetics is shaped by host-scale environmental selection and dispersal limitation. We then show how this allows both host- and microbe-scale environmental selection to govern spatial variation in Aphaenogaster microbiota. Finally, we discuss the possibility that microbe-scale dispersal limitation also impacts spatial variation in Aphaenogaster microbiota and that this, in turn, may contribute to spatial variation in Aphaenogaster genetics. Ultimately, our results help to shed light on the myriad of interacting factors governing spatial variation in HA microbiota, including the potential for complex, bidirectional interactions between host- and microbe-scale processes.