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

Thu Mar 21 15:05:14 UTC 2019

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>
>
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>
> *From:* cnidarian-dinoflagellate-symbiosis-bounces at auburn.edu 
> <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>
> *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
>
> 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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