[Coral-List] [Cnidarian-dinoflagellate-symbiosis] genetic connectivity of Symbiodinium individuals within a single colony

[Baker, Andrew]

Hi Thomas

I understand, but I think the same process is involved, i.e. acquisition of symbionts from the environment, presumably via the coelenteron. My feeling is that if its happening (or not) at the level of ITS2, its also happening at the level of strain. If the possibility exists that different ITS2 types can enter an adult system, why would that same process not allow the entrance of other closely-related strains of the same ITS2 type?

PS – don’t get me wrong, happy to still see these discussions ongoing, even if they are now fully mature and ought to have their own vote by now…

Andrew

_______________________
Andrew C. Baker, M.A. (Cantab.), Ph.D.
Associate Professor
Department of Marine Biology and Ecology
Rosenstiel School of Marine and Atmospheric Science
University of Miami
4600 Rickenbacker Cswy.
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From: Thomas Krueger <thomas.krueger at epfl.ch>
Sent: Thursday, March 21, 2019 11:05 AM
To: Baker, Andrew <abaker at rsmas.miami.edu>; Mikhail Matz <matz at utexas.edu>
Cc: cnidarian-dinoflagellate-symbiosis at gump.auburn.edu; coral-list at coral.aoml.noaa.gov
Subject: Re: [Cnidarian-dinoflagellate-symbiosis] genetic connectivity of Symbiodinium individuals within a single colony


Hi,

I am not talking about a shift in symbiont ITS2 type. This is not the 18-year discussion that has been going on whether corals can switch to a new symbiont ITS2 type or whether it has already been there in the background to begin with. I am talking about the genetic structure of the dominating symbiont type in a colony and whether/how much newcomers of the same symbiont type from the water column contribute to the gene pool of the symbiont community in order for selective forces to be able to act.

Cheers,

Thomas
--
Thomas Krueger Postdoctoral Researcher
Laboratory for Biological Geochemistry | École polytechnique fédérale de Lausanne (EPFL)

On 21.03.2019 14:50, Baker, Andrew wrote:
Hi Misha

I’m afraid I have to disagree. We simply do not know how often exogenous symbionts are acquired from the environment. My suspicion is that it happens all the time, just at a very low level, and those symbionts have a very hard time displacing a huge population of resident symbionts. Think of them as mutant alleles in a very large population. Most of them are neutral and come and go all the time and we never notice – in part because we don’t sample an entire colony when we study this. But occasionally some symbionts are acquired that can be positively selected for, and this selection is much more powerful if a bleaching event first removes much of the standing stock of symbionts (thereby reducing the effective population size and allowing the “adaptive mutant” to spread through the population, to continue with the popgen metaphor).

Of course this does not happen to the same degree with all species of coral and symbiont. For example, I think D. trenchii is pretty good at getting into corals, and not just at the larval acquisition stage. But I don’t think it’s the only symbiont that can do this.

There are lines of evidence that point in both directions and of course that means it might be different in different coral species, or under particular circumstances. So I’m just cautioning against making emphatic statements like “no, corals cannot switch symbionts for a new strain as adults” (note: my view above is expressed as a “suspicion” (albeit one based on some experience) hence readers are free to take it or leave it!

I will also note that this same discussion has been playing out for at least 18 year…. Apparently, it has still not yet come of age!

Cheers

Andrew

_______________________
Andrew C. Baker, M.A. (Cantab.), Ph.D.
Associate Professor
Department of Marine Biology and Ecology
Rosenstiel School of Marine and Atmospheric Science
University of Miami
4600 Rickenbacker Cswy.
Miami, FL 33149, USA
Voice: +1 (305) 421-4642
Fax: +1 (305) 421-4642
Email: abaker at rsmas.miami.edu<mailto:abaker at rsmas.miami.edu>
Visit the lab on facebook by clicking here<https://nam01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.facebook.com%2Fcr2lab&data=02%7C01%7Cabaker%40rsmas.miami.edu%7Cad367f2d91fe4833e06508d6ae0ea336%7C2a144b72f23942d48c0e6f0f17c48e33%7C0%7C0%7C636887775260276779&sdata=1KEhvqB2Qj73gZ9h96MWhicYc9eWxsPEuiyrCU%2FpS8U%3D&reserved=0>

From: cnidarian-dinoflagellate-symbiosis-bounces at auburn.edu<mailto:cnidarian-dinoflagellate-symbiosis-bounces at auburn.edu> <cnidarian-dinoflagellate-symbiosis-bounces at auburn.edu><mailto:cnidarian-dinoflagellate-symbiosis-bounces at auburn.edu> On Behalf Of Mikhail Matz
Sent: Thursday, March 21, 2019 9:54 AM
To: Thomas Krueger <thomas.krueger at epfl.ch><mailto:thomas.krueger at epfl.ch>
Cc: cnidarian-dinoflagellate-symbiosis at gump.auburn.edu<mailto:cnidarian-dinoflagellate-symbiosis at gump.auburn.edu>; coral-list at coral.aoml.noaa.gov<mailto:coral-list at coral.aoml.noaa.gov>
Subject: Re: [Cnidarian-dinoflagellate-symbiosis] genetic connectivity of Symbiodinium individuals within a single colony

you got it, Thomas. No, corals cannot switch symbionts for a new strain as adults. Think of symbionts as efficient parasites that never give up their host. Yes, symbionts can infect only the new generation of corals, so, from popgen point of view, coral generations = symbionts generations.

Misha Matz

On Mar 21, 2019, at 5:34 AM, Thomas Krueger <thomas.krueger at epfl.ch<mailto:thomas.krueger at epfl.ch>> wrote:

Here is a curious question: If the symbiont community in a coral host, as some publications suggest, consists of a single genet (i.e. genetically identical individuals aka clones), how can bleaching ever act as a positive selective force and reshape the surviving residual population towards a more heat resistant one? It literally would require uptake of genetically different individuals (of the same species) from the water column to diversify the genetic pool. Has someone used sequencing data to look at whether it is the residual population that recolonizes a bleached coral or whether it receives new settlers from the water column? If a single genet of Symbiodinium in colonies is really a dominating feature and if it does not change through bleaching events, then horizontal transmission might not really be such a big thing and there is little exchange with environmental Symbiodinium populations in the adult stage (exchange maybe, but not to the point that it reshapes colonies to the point that we can detect an altered genetic pool of the dominating species). This in turn would mean that the coral's larval and juvenile stage is the crucial stage that shapes the holobiont assemblage for the symbiont side. Any thoughts?

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