Abstract
Understanding biodiversity patterns is a major goal of ecology and evolution. This extends to the biodiversity within host organisms. In these cases, the biodiversity patterns and members of those
communities can be critically important for host fitness. Understanding how environmental variables
affect the composition of these communities, how host relatedness might affect these communities,
and even how the timing of island formation might trickle down to affect these communities helps
further the goal of understanding and eventually predicting these patterns. In my first chapter, I use
the local Rocky Mountainsnail (Genus: Oreohelix) and knowledge of their relationship to limestone
in their environment to assess whether this environment factor contributes to microbial community
assembly patterns across multiple sites in central Idaho. We find that the presence of calcium-rich
rocks at a site does drive a small amount of variation in bacterial community assembly in the snails,
but not in the soils nearby. In the second chapter, I characterize the microbial ecology of the endemic
Galápagos land snails for the first time. This chapter includes the assessment of various factors, such
as island age, vegetation zones, and host snail species on the fecal and substrate bacterial and fungal
alpha diversity and composition of this system. We find that Naesiotus species are all dominated by
two bacterial taxa, but that the fungal taxa are both not well documented in the reference databases
and the snail samples share most of their most abundant taxa in common with their environment. We
also find that microbial diversity patterns in our data do not follow the same patterns as many of the
macro-organisms in the Galápagos. Finally, in the third chapter, I continue with the Galápagos
Naesiotus land snails by exploring the use phylogenetic comparative methods to uncover insights into
the historical relationships between host snails and the bacterial taxa that live within. These methods
allow us to assess the phylogenetic signal as a way to test phylosymbiosis as well as obtain significant
covariances between microbial taxa that, in tandem with phylogenetic relationships of some of the
microbial orders, may suggest that there was a shift in multiple microbial relative abundances that
took places during a colonization event.