Getting the Hologenome Concept Right: an Eco-Evolutionary Framework for Hosts and Their Microbiomes

TLDR

Host–microbiota symbioses are complex, and the holobiont–hologenome framework has emerged as a multilevel, multipartite concept that requires a shared lexicon to distinguish it from related ideas such as coevolution. The authors aim to clarify when the holobiont and hologenome vocabulary should be applied and whether these concepts serve as a null hypothesis or are restricted to specific host–microbe interactions.

Abstract

Given the complexity of host-microbiota symbioses, scientists and philosophers are asking questions at new biological levels of hierarchical organization-what is a holobiont and hologenome? When should this vocabulary be applied? Are these concepts a null hypothesis for host-microbe systems or limited to a certain spectrum of symbiotic interactions such as host-microbial coevolution? Critical discourse is necessary in this nascent area, but productive discourse requires that skeptics and proponents use the same lexicon. For instance, critiquing the hologenome concept is not synonymous with critiquing coevolution, and arguing that an entity is not a primary unit of selection dismisses the fact that the hologenome concept has always embraced multilevel selection. Holobionts and hologenomes are incontrovertible, multipartite entities that result from ecological, evolutionary, and genetic processes at various levels. They are not restricted to one special process but constitute a wider vocabulary and framework for host biology in light of the microbiome.