Evolution and Coral

[MCsaxmaster]

<a href=showthread.php?s=&postid=12545309#post12545309 target=_blank>Originally posted</a> by Poorcollegereef
Unfortunately I am less aware about larval stages, but do you know the larval or developmental stages differ or do not differ between coarllimorphs, scleractinians, and other other cnidarians. Just a though... forgive me if I have errored

Hmmmm, that's a good question. I'm not aware of anyone that has worked with corallimorph planulae. I wouldn't necessarily expect to see any big differences between coral larval development and corallimorph larval development though. I'm not sure you'd even see much of a difference between hexacorals and octocorals except that the octocorals produce 8 septa and the hexacorals only 6 as they are nearing competency.

 

[Poorcollegereef]

I was wondering if there was any stage in the development where a vestigial "part" (for the lack of a better term) is present. If following the the evolution from skeleton producing/calcifing to "naked" or vice versa would there be a development stage of an planula where a "naked" corallimorph may have the potential ability to calcify a skeleton, but as the larva progresses the process is lost.

I would think that the response to the environmental conditions would likely occur at the larval stages and that the beginning of the split between scleractinia and corallimorphs as you explained would have been determined by the survival rates of coral larva and their ability to compete or not compete for calcium and/or substrate real estate

 

[MCsaxmaster]

<a href=showthread.php?s=&postid=12551733#post12551733 target=_blank>Originally posted</a> by Poorcollegereef
I was wondering if there was any stage in the development where a vestigial "part" (for the lack of a better term) is present. If following the the evolution from skeleton producing/calcifing to "naked" or vice versa would there be a development stage of an planula where a "naked" corallimorph may have the potential ability to calcify a skeleton, but as the larva progresses the process is lost.

I would think that the response to the environmental conditions would likely occur at the larval stages and that the beginning of the split between scleractinia and corallimorphs as you explained would have been determined by the survival rates of coral larva and their ability to compete or not compete for calcium and/or substrate real estate

Good questions, but you one won't see the sorts of things you're talking about. Planulae don't calcify. Corals don't begin to calcify until about a day or two after they settle. There's a lot of rearrangement that has to go on before they even have the tissues properly organized for calcification. Thus, you wouldn't see these sorts of changes.

What IS definitely worth looking for is pseudogenes in corallimorphs that are homologous to calcification genes in scleractinians. Unfortunately, we haven't identified most of those genes in scleractinians yet. When we do, I'd be surprised if many were not still present the genomes of corallimorphs, but in a non-functional or reduced-function state. Many of the genes involved in calcification are going to be things like just normal house-keeping genes that have been co-opted. For example, all cells need calcium channels, calcium pumps, proton pumps, etc. Those in corals may be ordinary ones that are really going to town in where the corals are actively calcifying, or they may be slightly modified. One subunit of a calcium channel involved in calcification has been cloned, and is highly conserved and homologous to one present in basically all metazoans.

Anyway, there's that. I hope that answers the question.

Chris

 

[willis87]

does anyone know of a good website or quick reference guide which shows the basic fossil record ? I need some touching up to put a lot of this stuff in perspective. Any kind of earthly time line would be good.

 

[MCsaxmaster]

Wikipedia might be useful here as a general reference.

The entire period of time we've talked about is encompassed by the Phanerozoic epoch (545 mya to present).

http://en.wikipedia.org/wiki/Phanerozoic

The Phanerozoic is divided into three eras:

Paleozoic (545-250 mya): rudist and tabulate corals were major reef builders as were a number of other critters which generally aren't that went extinct or aren't that important today. Scleractinian corals didn't exist yet, but their ancestors probably started to show up near the end of this period.

http://en.wikipedia.org/wiki/Paleozoic

Mesozoic (250-65 mya): the Paleozoic ends with huge extinction that really monkies things up. The Mesozoic consists of the Triassic, Jurassic, and Cretaceous periods. Dinosaurs originate in the middle Triassic, and we have are first undisputable scleractinian corals (modern stony corals). There are extinction events at the end of the Triassic and Jurassic. Corals hit a hickup, but keep on trucking. During the Cretaceous reef-building slows way down, probably due to changes in sewater chemistry. At the end of the Cretaceous most species on Earth die, including the dinosaurs (minus birds). Coral diversity declines substantially, but they survive.

http://en.wikipedia.org/wiki/Mesozoic

Cenozoic (65 mya to present): 10 million years in there is a major geologic event (Paleocene Eocene Thermal Maximum) that causes rapid global warming and ocean acidification (though probably much slower than is currently happening). Coral reefs pretty much disappear for 5 million years, but the survivors eventually pop back up and resume reef-building as conditions improve globally. Reef-building by primarily scleractinian corals, coralline algae, and some green alage (e.g., Halimeda) is pretty strong until present.

http://en.wikipedia.org/wiki/Cenozoic

Hope that helps.

Chris

 

[willis87]

thanks sax master.

 

[willis87]

i think what i am really looking for is a species specific and detailed timeline/ graph or physical representation from period to epoch. I have found a few whilst surfing but they are all rather general with regard to marine life

 

[cutegecko3]

www.accessexcellence.org/.../coralgene2c.jpg
Here is a interesting read.It backs up what i said about identifining corals species by morphology is wrong.

 

[cutegecko3]

Sorry about that.I cant seem to get the link to work.The name of the article is"Coral family tree reorganized,result of DNA anlyses"if anyone is interested.

 

[MCsaxmaster]

If you guys can access Nature, the article is here:

http://0-web.ebscohost.com.uncclc.c...e1f9a-7808-4cc1-b4ec-aa99dfb32334@sessionmgr9

There's still plenty of work to be done in resolving evolutionary relationships among corals.