title: Broadcast Spawning CoralMussismilia hispidaCan Vertically Transfer its Associated Bacterial Core.
abstract: The hologenome theory of evolution (HTE), which is under fierce debate, presupposes that parts of the microbiome are transmitted from one generation to the next [vertical transmission (VT)], which may also influence the evolution of the holobiont. Even though bacteria have previously been described in early life stages of corals, these early life stages (larvae) could have been inoculated in the water and not inside the parental colony (through gametes) carrying the parental microbiome. HowSymbiodiniumis transmitted to offspring is also not clear, as only one study has described this mechanism in spawners. All other studies refer to incubators. To explore the VT hypothesis and the key components being transferred, colonies of the broadcast spawner speciesMussismilia hispidawere kept in nurseries until spawning. Gamete bundles, larvae and adult corals were analyzed to identify their associated microbiota with respect to composition and location.Symbiodiniumand bacteria were detected by sequencing in gametes and coral planula larvae. However, no cells were detected using microscopy at the gamete stage, which could be related to the absence of those cells inside the oocytes/dispersed in the mucus or to a low resolution of our approach. A preliminary survey ofSymbiodiniumdiversity indicated that parental colonies harboredSymbiodiniumclades B, C and G, whereas only clade B was found in oocytes and planula larvae [5 days after fertilization (a.f.)]. The core bacterial populations found in the bundles, planula larvae and parental colonies were identified as members of the generaBurkholderia, Pseudomonas, Acinetobacter, Ralstonia, InquilinusandBacillus, suggesting that these populations could be vertically transferred through the mucus. The collective data suggest that spawner corals, such asM. hispida, can transmitSymbiodiniumcells and the bacterial core to their offspring by a coral gamete (and that this gamete, with its bacterial load, is released into the water), supporting the HTE. However, more data are required to indicate the stability of the transmitted populations to indicate whether the holobiont can be considered a unit of natural selection or a symbiotic assemblage of independently evolving organisms.
authors.affiliation: Institute of Microbiology, Federal University of Rio de Janeiro Rio de Janeiro, Brazil.
authors.forename: Deborah C A
authors.initials: DC
authors.lastname: Leite
authors.affiliation: Institute of Microbiology, Federal University of Rio de Janeiro Rio de Janeiro, Brazil.
authors.forename: Pedro
authors.initials: P
authors.lastname: Leão
authors.affiliation: Institute of Biology, Federal University of Rio de Janeiro Rio de Janeiro, Brazil.
authors.forename: Amana G
authors.initials: AG
authors.lastname: Garrido
authors.affiliation: Institute of Microbiology, Federal University of Rio de Janeiro Rio de Janeiro, Brazil.
authors.forename: Ulysses
authors.initials: U
authors.lastname: Lins
authors.affiliation: Institute of Microbiology, Federal University of Rio de JaneiroRio de Janeiro, Brazil; Instituto Coral VivoSanta Cruz Cabrália, Brazil.
authors.forename: Henrique F
authors.initials: HF
authors.lastname: Santos
authors.affiliation: Instituto Coral VivoSanta Cruz Cabrália, Brazil; National Museum, Federal University of Rio de JaneiroRio de Janeiro, Brazil.
authors.forename: Débora O
authors.initials: DO
authors.lastname: Pires
authors.affiliation: Instituto Coral VivoSanta Cruz Cabrália, Brazil; National Museum, Federal University of Rio de JaneiroRio de Janeiro, Brazil.
authors.forename: Clovis B
authors.initials: CB
authors.lastname: Castro
authors.affiliation: Department of Microbial Ecology, Centre for Ecological and Evolutionary Studies, University of Groningen Groningen, Netherlands.
authors.forename: Jan D
authors.initials: JD
authors.lastname: van Elsas
authors.affiliation: Institute of Biology, Federal University of Rio de JaneiroRio de Janeiro, Brazil; Instituto Coral VivoSanta Cruz Cabrália, Brazil.
authors.forename: Carla
authors.initials: C
authors.lastname: Zilberberg
authors.affiliation: Institute of Microbiology, Federal University of Rio de JaneiroRio de Janeiro, Brazil; Instituto Coral VivoSanta Cruz Cabrália, Brazil.
authors.forename: Alexandre S
authors.initials: AS
authors.lastname: Rosado
authors.affiliation: Institute of Microbiology, Federal University of Rio de JaneiroRio de Janeiro, Brazil; Instituto Coral VivoSanta Cruz Cabrália, Brazil.
authors.forename: Raquel S
authors.initials: RS
authors.lastname: Peixoto
keywords: Symbiodinium; bacteria; coral core microbiome; holobiont; microbiota transmission