Abstracts (first author)
No host is an island: the impact of multiple symbionts on pairwise interactions
Host – symbiont interactions, though often studied as a pairwise process, rarely occur in isolation. In most cases individual host populations often interact, and potentially coevolve, with multiple symbiont populations concurrently. These pairwise coevolutionary interactions will be affected by the biotic environment in which they take place and vice versa, however the complexity of natural populations make these effects hard to unravel in the wild. Experimental evolution provides an excellent framework in which to examine the impact of these rival symbiotic interactions, as (co)evolutionary dynamics can be observed through time in communities of known biotic structure. Using this approach we examine the conflict between two otherwise independent symbionts of the same host; a parasitic lytic phage and a facultatively mutualistic plasmid, both native to the bacteria Pseudomonas fluorescens. We find that the presence of a second symbiont has major effects on the ecology and evolution of these interactions in both directions. Firstly we show that the presence of coevolving phages accelerates the loss of plasmids under conditions in which they are parasitic, but not mutualistic. Secondly we demonstrate that plasmid carriage alters the trajectory of bacteria-phage coevolution, favouring generalist phage-resistance strategies among hosts also carrying the plasmid. This study therefore shows the impact community complexity has on pairwise host – symbiont interactions, and in turn how these interactions can shape the community in which they are embedded.