Conceptualization of the Holobiont Paradigm as It Pertains to Corals.

Tamar L Goulet,Ivan Erill,Marina S Ascunce,Sheree J Finley,Gulnaz T Javan

doi:10.3389/fphys.2020.566968

Abstract

Corals’ obligate association with unicellular dinoflagellates, family Symbiodiniaceae form the foundation of coral reefs. For nearly a century, researchers have delved into understanding the coral-algal mutualism from multiple levels of resolution and perspectives, and the questions and scope have evolved with each iteration of new techniques. Advances in genetic technologies not only aided in distinguishing between the multitude of Symbiodiniaceae but also illuminated the existence and diversity of other organisms constituting the coral microbiome. The coral therefore is a meta-organism, often referred to as the coral holobiont. In this review, we address the importance of including a holistic perspective to understanding the coral holobiont. We also discuss the ramifications of how different genotypic combinations of the coral consortium affect the holobiont entity. We highlight the paucity of data on most of the coral microbiome. Using Symbiodiniaceae data, we present evidence that the holobiont properties are not necessarily the sum of its parts. We then discuss the consequences of the holobiont attributes to the fitness of the holobiont and the myriad of organisms that contribute to it. Considering the complexity of host-symbiont genotypic combinations will aid in our understanding of coral resilience, robustness, acclimation, and/or adaptation in the face of environmental change and increasing perturbations.

Highlights

Linnaeus hypothesized that gorgonian corals were plants which metamorphosed into animals
If the traits of a coral holobiont are driven by the holobiont consortium, is the holobiont the unit of selection? Does the holobiont depend on its specific consortia, or just on their physiological roles? And, does theoretical modeling, for example, coral survival under different climate conditions, require incorporating holobiont variables?
The coral holobiont is a consortium of phylogenetically disparate entities co-existing in a coral

Summary

INTRODUCTION

Linnaeus hypothesized that gorgonian corals were plants which metamorphosed into animals. At the core of the coral reef ecosystem is the obligatory symbiosis between corals and dinoflagellate algae, family Symbiodiniaceae This mutualism relies on “access to metabolic capabilities” and “protection from antagonists” (Douglas, 2010). Other DNA regions provided within-clade, population, and individual level resolution (reviewed in Goulet et al, 2019) Recently were these dinoflagellates placed in the family Symbiodiniaceae (LaJeunesse et al, 2018). Coral species host specific Symbiodiniaceae genera and types, and these do not change even under stressful conditions (Goulet, 2006, 2007), shuffling of the proportion of existing types may occur (Berkelmans and van Oppen, 2006), as well as transient or low level Symbiodiniaceae (Silverstein et al, 2012). The concept of specificity commands attention since, whether the holobiont entity can change or not affects interpretation of coral acclimation, adaptation, resilience, and persistence (Figure 1)

Findings

DISCUSSION

CONCLUSION