"Holobiont" is a term formulated by Lynn Margulis to describe the collective organism emerging from both an individual animal and its associated microbiome. Among other meanings, it represents the host-microbiome relationship. It is a step beyond the simple relationship of [[Examples of mutualism|mutualism]], into an understanding of bodies as ecosystems. Though initially attributed to animals, plants are now also recognized as having their own biomes as illustrated by the rhizosphere and phyllosphere. The aggregation of genes within a holobiont is the hologenome. The hologenome represents the composite organism and its behavioral tendencies within its environment. - Microbial influence on altruistic behavior has [successfully simulated](https://pmc.ncbi.nlm.nih.gov/articles/PMC5241693/) hosts that outcompete their rivals when altruism is genetically prevalent at the microbial level. A holobiont is an organism and an ecosystem [[interbeing]] together. The otherness of the microbiome becomes incorporated into the matter of the host. This relationship [challenges](https://journals.asm.org/doi/10.1128/msystems.00028-16) the existing hierarchical framework of the phylogenetic tree. The concept of the biological individual is a [convenient](https://pubmed.ncbi.nlm.nih.gov/23397797/) fiction useful for directing research, but symbiosis is the biological reality. Any degree of cooperation, [such as that between lichens and tree species](https://www.sciencedirect.com/science/article/abs/pii/S016953472200057X), represents a form of functional integration. "[Terrain theory](https://en.wikipedia.org/wiki/Germ_theory_denialism#Terrain_theory)," a discredited branch of pathology, provides an interesting perspective of the host body from the standpoint of the microorganism, with implications for the overall health of the holobiont. %% ## Notes ### Can Microbes Encourage Altruism #### Summary - Microbes can alter behavior in their hosts - *[Ophiocordyceps unilateralis](https://en.wikipedia.org/wiki/Ophiocordyceps_unilateralis)*, Zombie Ant Fungus manipulates ant behavior to leave colony and attach to leaves that provide the fungus with food. - *[Dicrocoelium dendriticum](https://en.wikipedia.org/wiki/Dicrocoelium_dendriticum)*, Lancet Liver Fluke compels ants to wait atop blades of grass and increase the chances that a grazing animal will eat them. - A healthy debate over the role of altruism exists throughout the history of evolutionary theory. - One group of scientists has demonstrated that small populations of microbes that can influence altruistic behaviors outcompete other microbe populations inside their hosts. - This opens up new possibilities for examining established symbioses between microbes and humans, such as how [the microbiome in a healthy colon produces serotonin](https://www.nature.com/articles/526312a). - [full text](https://www.quantamagazine.org/can-microbes-encourage-altruism-20170629/) #### Highlights * according to various animal studies, **gut flora alter neural and endocrine function in ways that alter hosts’ social interactions.** * **The connection between a host’s microbiome composition and its resulting behavior is known as the “microbiota-gut-brain axis.” It’s possible, then — though not yet proved — that microbe-produced compounds could influence neural processes that give rise to generous impulses.**