KSEF RDE: Developing a spider model system for understanding interactions among endosymbionts

Symbiotic microbes can importantly influence the health and behavior of their eukaryotic hosts. Yet for vertebrates, the complexity and variability of microbe assemblages make it exceedingly difficult to parse the functionality and interactions among microbial players. Insects, in contrast, often have simple microbial communities dominated by few taxa that are vertically transmitted across generations and are stable over evolutionary time. We propose the novel approach of using spiders, non-insect arthropods, as a model system that bridges these two extremes. The spider Mermessus fradeorum is infected by up to three different bacterial symbionts, two of which induced mutually incompatible reproductive manipulations in their hosts. We hypothesize that the bacteria are competing with one another within the host, affecting both phenotypic expression and probability of bacterial transmission to the next generation, which in turn generates the diversity of infection types observed in the field. We have further surveyed additional spider species, and identified 3 others that appear to have similarly dynamic interactions among bacterial taxa. We will 1) establish laboratory colonies of 2-3 spider species, and experimentally manipulate symbiont infection via antibiotic treatment, 2) characterize the full microbiome of the spider lineages via next-gen sequencing, and 3) develop diagnostic primers that can distinguish between closely related bacterial strains, to monitor bacterial titer via qPCR. These necessary tools will allow subsequent inquiry into the competitive mechanisms among microbial symbionts, consequences for host population dynamics, and the mechanisms by which symbionts manipulate host biology.