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

Sat Mar 23 01:25:00 UTC 2019

Hi guys

Yes, a few papers come to mind that provide evidence for that exogenous symbiont acquisition from the environment can occur at the adult stage:

Lewis & Coffroth 2004 Science
Coffroth et al. 2010 PLoS One
Boulotte et al. 2016 ISME J
(There are probably more, sorry if I missed someone's paper here...)

Yes labeling symbionts is a good idea. We tried this a few years ago with stains, but the stain dilutes out from the symbionts as they grow and divide so you have to act quickly. Someone should try it again...!

Interesting to think about facultative scleractinian symbiosis in this regard (e.g. Oculina and Astrangia), and Aiptasia, and clams. Do we think that scleractinians are unique in being closed systems as adults? I think it's more parsimonious to think that all these organisms can acquire symbionts as adults, rather than concluding its possible for some but not others.

My main point is that we shouldn’t be too dogmatic about these things, which is I guess why I felt I had to respond to Misha's answer to Thomas's question. I'm not trying to counter dogma with more dogma. Just saying we have to keep an open mind, and to do that I have to argue the counterfactual. 

Friday night! No more email for me...!

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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-----Original Message-----
From: sarah davies <daviessw at gmail.com> 
Sent: Friday, March 22, 2019 10:01 AM
To: Baker, Andrew <abaker at rsmas.miami.edu>
Cc: Mikhail Matz <matz at utexas.edu>; Thomas Krueger <thomas.krueger at epfl.ch>; cnidarian-dinoflagellate-symbiosis at gump.auburn.edu; coral-list at coral.aoml.noaa.gov
Subject: Re: [Coral-List] [Cnidarian-dinoflagellate-symbiosis] genetic connectivity of Symbiodinium individuals within a single colony

Hi Andrew et al,

I couldn't help myself....

My gut feeling about this whole idea of novel uptake as an adult is that we have been trying to find data to support the Adaptive Bleaching Hypothesis (i.e. syms leave to allow novel sym strains to
arrive) for many years and there is no "nail in the coffin" type evidence. There are two mechanisms, which are not mutually exclusive, that may explain the switching phenomenon:

1. There are rare "mutant alleles" (i.e. background D's or whatever else you might imagine) that are present in a coral colony and given the right opportunity (i.e. bleaching when competitive interactions between symbionts change/host control of the symbiosome changes etc) they become dominant. To detect the presence of these background types we would need to grind up the whole colony and sequence very deeply to ensure that we could confidently say that those symbionts were not present.
2. Adults can uptake novel symbionts, which again, under the right circumstance (i.e. bleaching), these "mutant alleles" overtake a population.

So, when you say "D. trenchii is pretty good at getting into corals", I still don't think we have the ability to disentangle whether that symbiont was there is background proportions or if that symbiont was a novel uptake as an adult from the environment. I don't think that we can accept 2 without testing rigorously for 1. However showing evidence for 1 is perhaps an easier path. As a personal anecdote have seen S. siderastrea switch from C-->D under severe bleaching in tank experiments ran with instant ocean so there were no environmentally available symbionts, I think they were just there in background amounts that are rarely detected (i.e. option 1). In my mind there is decent evidence for option 1, and less concrete evidence for option 2 since it is more difficult to provide support for. Perhaps labeling some mutant sym strain and trying to infect adults under stress would be fun- Maybe someone has done this and I missed it? This would be a great way to show that 2 is possible without the need for provide concrete evidence against 1.

This is a fun conversation that I wish was in person.

Cheers
Sarah

On Fri, Mar 22, 2019 at 9:32 AM Baker, Andrew via Coral-List <coral-list at coral.aoml.noaa.gov> 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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--
Sarah W. Davies M.Sc. Ph.D.
Assistant Professor
Department of Biology
Boston University
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