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

Fri Mar 22 14:00:44 UTC 2019

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>
> Visit the lab on facebook by clicking here<https://www.facebook.com/cr2lab>
>
> 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?
>
> _______________________________________________
> Cnidarian-dinoflagellate-symbiosis mailing list
> Cnidarian-dinoflagellate-symbiosis at auburn.edu<mailto:Cnidarian-dinoflagellate-symbiosis at auburn.edu>
> http://listserv3.auburn.edu/mailman/listinfo/cnidarian-dinoflagellate-symbiosis<https://nam01.safelinks.protection.outlook.com/?url=http%3A%2F%2Flistserv3.auburn.edu%2Fmailman%2Flistinfo%2Fcnidarian-dinoflagellate-symbiosis&data=02%7C01%7Cabaker%40rsmas.miami.edu%7Cfa18db2e6d594e020ebc08d6ae069a9b%7C2a144b72f23942d48c0e6f0f17c48e33%7C0%7C0%7C636887740726798609&sdata=w79YrTi1Nt3bMgPdhwsSnZ%2BSc%2FZOWzjlsmVGBxfje40%3D&reserved=0>
> _______________________________________________
> Coral-List mailing list
> Coral-List at coral.aoml.noaa.gov
> https://coral.aoml.noaa.gov/mailman/listinfo/coral-list

--
Sarah W. Davies M.Sc. Ph.D.
Assistant Professor
Department of Biology
Boston University
Office: (617) 353-8980
Lab: (617) 353-6956
Twitter @DaviesswPhD
Email: daviessw at bu.edu
Website: http://sites.bu.edu/davieslab/