Holobionts and their hologenomes: Evolution with mixed modes of inheritance

Abstract

Symbioses are ubiquitous and have played an influential role in the evolution of life on Earth. Genomic studies are now revealing a huge diversity of associations among hosts and their microbiotas, allowing us to characterize their complex ecological and evolutionary dynamics. The different transmission modes and the asynchronous cell proliferation of the numerous symbionts associated with one host generate a genomic conflict ought to be solved. Two disputing views have been used to model and predict the outcome of such conflicts. The traditional view is based on community ecology, and considers that selection at the level of individuals is sufficient to explain longstanding associations among species. A new perspective considers that the host and its associated microbiota constitute a biological entity called holobiont, and that regarding it as a higher-level unit of selection is unavoidable to understand phenotypic evolution. Novel extended phenotypes are often built through symbiotic interactions, allowing the holobiont to explore and survive in distinct environmental conditions, and may evolve in a Lamarckian fashion.

Is Host Filtering the Main Driver of Phylosymbiosis across the Tree of Life?

“…This means that phylosymbiosis alone cannot be taken as a proof of an intimate and long-term coevolution between the host and the microbiota. While this point was acknowledged in previous reports ( 11 , 15 , 34 ), we explicitly show it using simulations. We note here that our simulations did not explore intraspecific variability compared to interspecific variability.…”

Origins of human milk microbiota: new evidence and arising questions

“…core Gram negative bacteria in honey bees). 54 Similarly in humans, horizontal transfer of bifidobacteria and other bacteria from the environment and other household members likely contributes to the development of the infant gut microbiota, 55 regardless of breastfeeding. A fresh outlook based on principles of holobiont ecology 56 is required to better understand the functional importance of milk in vertical and horizontal bacterial transmission.…”

Cell lineage trees: the central structure plus key dynamics of biological aging and formulating the limiting problem of comprehensive organismal rejuvenation

“…Speciality of one particular process is not a sufficient reason to dismiss the arguments for the centrality of cell trees in biological aging. This host and guest aggregate together is called a holobiont, and it is being increasingly acknowledged as a new unit of biological organisation (Haag, 2018), playing a role in health and disease. The estimated number of bacteria in a human 'reference person' is 38 trillion (Sender et al, 2018), a significantly larger number than the estimated 30 trillion human cells.…”