Evolution and Coral

[greenbean36191]

20 years ago scleractinians were discovered in the ordovician and the permian.Very recent discoveries in china have pushed them back even further.I havent been able to find any published reports of it yet though.

There's no evidence of true scleractinians that early, and the view that the pre-Triassic scleractiniamorphs gave rise to modern Scleractinia isn't widely held. You could probably count all of the authors that have published in that vein on one hand and have a few fingers left over.

The most popular hypothesis is that prior to the late Triassic, Scleractinian were non-calcifying due to unfavorable conditions in the ocean. It's not clear whether those naked corals were primitively naked or they shared a lineage with the rugose or scleractiniamorph corals and just lost their skeletons when the oceans became unfavorable for calcification.

 

[cutegecko3]

I dont beleive there is any real morphological difference between scleractiniamorph corals and scleractinians.The literature describes differences but those differences are likely from corals in high flow.We know they grow very robust in those conditions compared to the same species in low flow.I could be wrong but its kind of like comparing a poodle to a great dane and calling them a different species.

 

[MCsaxmaster]

Ha, well to be fair most of the early anthozoans--some of which may or may not have been ancestors of scleractinians--are quite a bit different from Triassic scleractinians. It's really more like comparing fish to Great Danes There are fundamental morpholigical differences.

Rugose corals almost certainly didn't lead to scleractinians. The body plan is just very, very different--kind of like comparing spiders and shrimp, ha.

Scleractinians are almost certainly polyphyletic. Or rather, the group is polyphyletic if we group corallimorphs separately from scleractinians. There's growing evidence that calcification developed and perhaps disappeared at least twice if not many times in the groups leading up to scleractinians and corallimorphs. It may be that these proto-scleractinians diverged from each other, one group began calcifying, and then the second group diverged into corallimorphs and a second scleractinian group which also began to calcify. Calcification may have been developed, reduced/lost, and redeveloped in these groups as well.

The picture is becoming clearer, but more work has to be done to clarify the origins of the scleractinia and their relationship to other anthozoans.

Once we get scleractinians in the Triassic, however, the evolutionary history of most coral families is much clearer. There is still more to be done, but there are good fossil records for many coral families/genera.

It's an absolutely spectacular, wonderful, beautiful area of research

Chris

 

[MCsaxmaster]

<a href=showthread.php?s=&postid=12221896#post12221896 target=_blank>Originally posted</a> by cutegecko3
I dont beleive there is any real morphological difference between scleractiniamorph corals and scleractinians.The literature describes differences but those differences are likely from corals in high flow.We know they grow very robust in those conditions compared to the same species in low flow.I could be wrong but its kind of like comparing a poodle to a great dane and calling them a different species.

And just to be clear: the kinds of differences we see are not related to ecomorphs from different environments. They are fundamental differences in stucture--the equivalent of having a 4-chambered heart vs. a two-chambered heart vs. an aortic arch; the equivalent of having lungs vs. gills. These are not trivial differences

 

[cutegecko3]

Actinocyathus floriformis(rugose coral)looks identical to any lps(favites or acan.)in anybodys tank right now.I cant see how you can call that a completely different kind of animal.But whatever trips your trigger i guess.

 

[MCsaxmaster]

Are you serious???

Rugose corals have a completely different septal structure as compared to scleractinians. Sea anemones, zoanthids, and cerianthids are more similar in structure to scleractinians than rugose corals were. They also had calcitic skeletons, not aragonitic ones. I mean, these are not trivial differences. These are completely different animals--as different as elephants and crocodiles.

 

[greenbean36191]

Superficially yes, but the devil is in the details. Rugose corals are bilaterally symmetrical like zoanthids rather than radially like scleractinians. Their septae aren't arranged into regular cycles like modern stony corals. They also had calcite skeletons rather than aragonite, but that my have just been an artifact of the chemistry at the time rather than a real evolutionary difference. Some recent work suggests that some modern corals can lay down calcite too if conditions are right.

Edit: I watch a little TV and grab some food before I reply and I miss out on a few million years of evolution.

 

[MCsaxmaster]

I will note, however, that even in seawater chemistry analagous to what rugose and tubulate corals lived in, and in which they made essentially pure low-Mg calcite skeletons, modern corals still produce mostly aragonite with some low-Mg calcite. I do think there is some evolutionary or at least physiological significance to the CaCO3 polymorph. To suggest that it's a matter of only precipitating one polymorph or another is a bit short-sighted though, I think. Newly settled polyps will make a primarily calcitic basal plate and then start producing aragointe, for instance. Physiology plays a big role in determining the predominant mineral form produced, but not to the exclusion of all other forms.

Besides, they're probably precipitating amorphous CaCO3 to start and somehow converting it over to aragonite (maybe with vaterite inbetween). We don't know how they do that

 

[miwoodar]

I'm a crappy resource for informing you about coral evolution - - - I don't know much about it.

If I had to write a paper on evolution though - - - I would probably choose cichlids from Lake Malawi. Before I learned about them, I held two misconceptions:
1) evolution proceeds at a steady pace
2) it takes so long you can't possibly see it in action

The rivers that feed into Lake Malawi create breaks in the shoreline that fish can have difficulties crossing. As you study the fish on each side of the divides, you can literally see the species change in very tiny increments. It's amazing. For example, on one side of a divide a fish might have one tale spot. On the other side, the same species might have two spots. etc...then a new species.

OK...back to the purpose of the thread - coral evolution. It's not my paper anyways .

 

[seapug]

I came home from work yesterday to find the latest issue of Coral Magazine had arrived. It contains Part 1 of a series of articles about fossilized corals in the Red Sea. Anyone who's interested in this topic should pick it up.

 

[thecichlidpleco]

Okay, we are writing about the voyage of the beagle, and had to pick a chapter each, I chose coral formations in chpater 20. So I cannot choose to write about cichlids or some other point that Darwin did not witness on his voyage. And my chapter got split in two, and the first part doesnt relate to evolution, mroe to geologic time. He witnessed large coral colonies on one side of the island were bleached and dead, and because we and he also knew that corals cannot survive out of water for an extended period of time, he assumed that at one time the island was split by a channel and allowed water to consistently pass over the now dead colonies. The lagoon closed and created low tides over this colony and thus killed it by exposure.

Also, just like many can put praise jesus in their signature, I to can put what I want so please stay on "scientific" topic and not theology.

 

[cutegecko3]

DNA testing has proven that acropora has exploded into the diversity that we have now through hybridization from just a small variety of different types.You might think it absurd to claim a purple monster is the same species as a purple gemmifera.But that is what the evidence proves.Natural selection cannot increase genetic information,it only results in a loss of information by genetic isolation.Rugose corals are LPS stoney corals no matter who doesnt like it.They are not gone, they have changed slightly through hybridization and natural selection.

 

[cutegecko3]

And also the content of their skeletons has been replaced by different minerals,that is why we have fossils.

 

[miwoodar]

Huh?

Cichlidpleco - it's definitely a cool idea regarding your topic. I'm looking forward to following this thread!

 

[MCsaxmaster]

DNA testing has proven that acropora has exploded into the diversity that we have now through hybridization from just a small variety of different types.

Nnnnnooo In closely related sister taxa among corals we can document multiple hybridization events in the past, but that isn't necessarily unexpected for closely related species. The best examples here are the Montastraea annularis/faveolata/franksi complex, some Montipora and some Acropora. There are definitely some reproductive barriers to cross fertilization, but they have not always been sufficient to prevent hybridization. Acropora prolifera is an obvious example of reproductive barriers that are less than perfect. Genetic examples in the examples above demonstrate previous periods when reproductive isolation was weaker among some species, and there was hybridization. This happens in many organisms, at least until sufficient barriers evolve to prefent hybridization. Lots of work has been done on that with many animals and plants.

To suggest that we have a variety of Acropora species simply due to hybridization is pretty ridiculous though. Most species in the genus are reproductively isolated from the rest. We also have clear fossil records for many groups/species just within Acropora.

You might think it absurd to claim a purple monster is the same species as a purple gemmifera.But that is what the evidence proves.

Whoa, whoa, whoa, what are you talking about? That isn't even remotely true.

Natural selection cannot increase genetic information,it only results in a loss of information by genetic isolation.

Well yeah, no kidding. Mutation produces new DNA sequences. Natural selection eliminates detrimental mutations, rewards beneficial ones, and doesn't effect neutral ones (the vast majority of mutations are neutral).

Rugose corals are LPS stoney corals no matter who doesnt like it.

The first point to consider here, is that the term "LPS" us less than meaningless when it comes to phylogenetic relationships. Almost all coral families include species with fairly large polyps and very small polyps. Polyp size is not in any way diagnostic for anything except individual species and does not remotely imply relatedness.

As for the rugosa being synonamous with the scleractinia: if we consider any morphological or physiological characters whatsoever we can immediately see that they are completely different organisms. If the rugosa were considered synonamous with the scleractinians, we would also have to consider zoantharians, actinarians, tubiporans, alcyonaceans, etc., etc. as synonamous as well.

That would be on par with saying that really aren't any important differences between people, fish, chickens and frogs

They are not gone, they have changed slightly through hybridization and natural selection. [/B]

The rugosa are gone, as are the tabulata, there's no doubt about that. The scleractinians have indeed had a rich evolutionary history over the last 200 million years though

 

[cutegecko3]

A new sub-species of acropora is produced when the branches fuse together.They always grow outwards so they dont compete with each other for light.But in the very rare instance they grow towards each other and fuse a hybrid is produced.It is observed and i have actualy seen one.Genetic mutation producing any new genetic information is not observed.No one has ever observed something evolving from simple to complex.It is always the other way around.If you know of any example of that please let us know since we are discussing observable science here.Richard Dawkins was unable to answer that question so i doubt anyone else could either.

 

[miwoodar]

not applicable.

 

[MCsaxmaster]

A new sub-species of acropora is produced when the branches fuse together.They always grow outwards so they dont compete with each other for light.But in the very rare instance they grow towards each other and fuse a hybrid is produced.It is observed and i have actualy seen one.

........what???

Please pull up a couple of references that define the terms "subspecies" and "hybrid." This description is, to put it kindly, seriously flawed

Genetic mutation producing any new genetic information is not observed.

Genetic mutation changes DNA from one sequence to another. This is new genetic information, by definition. ALL mutations produce new genetic information.

No one has ever observed something evolving from simple to complex.It is always the other way around.If you know of any example of that please let us know since we are discussing observable science here.

If you would, please do a search for 'evolution of nylonase.' This is but one of countless examples

Richard Dawkins was unable to answer that question so i doubt anyone else could either.

Ha, well I think not since it is a very easy question to answer

 

[miwoodar]

Nnnnnooo In closely related sister taxa among corals we can document multiple hybridization events in the past, but that isn't necessarily unexpected for closely related species. The best examples here are the Montastraea annularis/faveolata/franksi complex, some Montipora and some Acropora. There are definitely some reproductive barriers to cross fertilization, but they have not always been sufficient to prevent hybridization. Acropora prolifera is an obvious example of reproductive barriers that are less than perfect. Genetic examples in the examples above demonstrate previous periods when reproductive isolation was weaker among some species, and there was hybridization. This happens in many organisms, at least until sufficient barriers evolve to prefent hybridization. Lots of work has been done on that with many animals and plants.

To suggest that we have a variety of Acropora species simply due to hybridization is pretty ridiculous though. Most species in the genus are reproductively isolated from the rest. We also have clear fossil records for many groups/species just within Acropora.



Whoa, whoa, whoa, what are you talking about? That isn't even remotely true.



Well yeah, no kidding. Mutation produces new DNA sequences. Natural selection eliminates detrimental mutations, rewards beneficial ones, and doesn't effect neutral ones (the vast majority of mutations are neutral).



The first point to consider here, is that the term "LPS" us less than meaningless when it comes to phylogenetic relationships. Almost all coral families include species with fairly large polyps and very small polyps. Polyp size is not in any way diagnostic for anything except individual species and does not remotely imply relatedness.

As for the rugosa being synonamous with the scleractinia: if we consider any morphological or physiological characters whatsoever we can immediately see that they are completely different organisms. If the rugosa were considered synonamous with the scleractinians, we would also have to consider zoantharians, actinarians, tubiporans, alcyonaceans, etc., etc. as synonamous as well.

That would be on par with saying that really aren't any important differences between people, fish, chickens and frogs




The rugosa are gone, as are the tabulata, there's no doubt about that. The scleractinians have indeed had a rich evolutionary history over the last 200 million years though


:beer:
Man - I wish my college had classes about marine environments and the ecology thereof. The closest I got were a few generalized classes that could be 'applied' for lack of a better term...ecology, genetics, biological statistics, cell bio, fisheries/wildlife management, and a limnology course. One last one - wastewater treatment and drinking water supply (it might as well have been called 'how to keep a really large fish tank').

 

[cutegecko3]

<a href=showthread.php?s=&postid=12232941#post12232941 target=_blank>Originally posted</a> by miwoodar
not applicable.

You dont believe a new species is formed from branch fusing,or is an observable genetic mutation increasing genetic information off topic?I kind of like the branch fusing myself it is very interesting.