Models of microbiome evolution incorporating host resource provisioning

Multicellular hosts and their associated microbial partners (i.e., microbiomes) often interact in mutually beneficial ways. Consequently, hosts may choose to allocate resources to regulate and recruit appropriate microbes. In doing so, hosts may incur an energetic cost, and in turn, these costs can affect host fitness. It remains unclear how hosts have evolved to balance the costs of expending resources to manage their microbiomes against the benefits that might accrue by doing so. We extended a previously-developed agent-based computational model of hostmicrobiome evolution by incorporating a resource provisioning process, whereby hosts provide resources to support beneficial microbes and suppress harmful microbes, with attendant fitness costs. Our results indicate that the ways and sources from which a host acquires microbes are crucial factors influencing the hosts willingness to provide resources, to regulate microbiome composition. The intensity of resource provisioning will depend, in part, on how much of their microbiome hosts contribute to, and obtain from, their environment: when hosts that engage in resource provisioning contribute a high percentage of their microbiome to the environment, then there is less evolutionary imperative for other hosts to also provide resources. Since resource provisioning incurs a fitness cost to the host, over evolutionary time, resource provisioning will not be favored. Additionally, if selection at the microbial level is not sufficiently strong, and the host obtains a high proportion of microbes from the environment, then the higher the proportion of beneficial microbes in the environment, the less the host is willing to provide resources.