Who thinks they know science?

[jsfakianos]

So, if you know science you must be able to predict that coral propagation without spawning (asexual versus sexual) will eventually produce a prompt kill-off of your colony :chat:.

I am starting to enjoy the spectacles of soft coral propagation. Every propagation webpage I see is actually talking about splitting corals and growing them, this is asexual reproduction. I haven't seen very much about the 'holy grail' of sexual reproduction.

I fear that the rapid growth of, let's say Xenia species, is simply the spreading of the single specimen. This would indicate that the telomeres of the genome would be shortening with each cell division. This is thought to be (in many scientific circles) how most eukaryotic cells age.

Often I hear about a complete Xenia colony killing over :blown:. Well, its of no surprise that if the telomeres aren't replenished the Xenia'a genome will look like that off an old man trying to return soup at a deli (sorry, I'm watching Sienfeld). Unless sexual reproduction occurs, colonies of all sorts will continue to die.

Sexual reproduction is one of the joys of being a coral :smokin:. I would love to open a discussion board focused on coral pornography.

Goodness, this is talked about on Star Trek.




Actually, I am just curious. I do not know if anyone knows enough about geriatrics (sp?) to contribute to the subject. However, I would love to hear any arguments of why a single specimen should be expected to be able to infinitly-asexually reproduce itself.




Thanks,
:tongue2:

[sculpin]

Are you certain that the usual rules of eukaryotic cell growth and reproduction apply to corals? I would be hesitant to claim that they do, knowing that asexual reproduction is a standard means of reproduction for many coral species in the wild in addition to sexual reproduction. I would therefore have to think that they have evolved a means of avoiding telomeric aging to some extent.

[jsfakianos]

I agree that the facts are not nailed down. However, I did not know that the standard could be either/or. I have only read a couple of books on corals. However, the books mentioned that sexual reproduction was the norm in the wild while asexual techniques where highlighted as probable tank inhabitant means for spreading.

I agree with you that nature would not propagate a dead-end lineage in a reef. However, I am not sure that nature would maintain both means of reproduction without repercussions for an organism that prefers one over the other.

Thank you for your reply Sculpin. I am very interested in including everyone in this discussion. I do not have a preconceived opinion. I am just interested in understanding
why a single specimen should be expected to be able to infinitly-asexually reproduce itself.

[sculpin]

Actually, I am of the opinion that asexual reproduction occurs as often or possibly more often than sexual reproduction for the subset of corals exposed to high currents and wave action (such as many Acroporidae). It is very common to find broken off pieces of viable coral in the inshore areas near outer reef walls. Some of these species need only be stable for 2-3 weeks in order to encrust, and thus asexually reproduce.

That said I think your hypothesis definitely needs to be considered. I would be very curious about the telomeric shortening of some of the Xenia clones, such as the red sea and X. elongata varieties, many of which have gone through hundreds of clonal divisions without a crash (just ask Brad Ward if you have any doubts). If you have the time and resources to do a telomeric analysis, X. elongata would probably be an excellent choice, as it can be grown out in large amounts with minimal effort.

[Mark]

I fear that the rapid growth of, let's say Xenia species, is simply the spreading of the single specimen. This would indicate that the telomeres of the genome would be shortening with each cell division. This is thought to be (in many scientific circles) how most eukaryotic cells age.

Often I hear about a complete Xenia colony killing over . Well, its of no surprise that if the telomeres aren't replenished the Xenia'a genome will look like that off an old man trying to return soup at a deli (sorry, I'm watching Sienfeld). Unless sexual reproduction occurs, colonies of all sorts will continue to die.


What an interesting and refreshing topic!:D

When it comes to corals, I do not think the threat of shortening telomeres through cell division applies. There are many examples of small polyped stony corals that are dated to be several hundred years old. An example would be some of the brain corals that are the size of a VW bug. One of that size can be seen on a reef in Trinidad. Small polyped stonies grow by cellular division. In fact, they are simply colonies of polyps. For them to cellularly divide for centuries and thus grow into gigantic colonies demonstrates to me that the threat does not exist. I mean, what's the difference between these colonies growing into a huge formation together compared to them growing separately through fragmentation. The cellular division and resulting growth is the same whether the colony stays as one, or fragmened colony.

Also as Sculpin noted, asexual reproduction is quite common. I've forgotten a lot from my genetics courses, but I think the shortening of telomeres and eventual aging of cells occurs in higher organisms. Aging hardly seems to be common in corals. In fact, they can live forever, if it weren't for environmental factors like predation, competition, and environmental stress through disease, higher temps, etc.

Some organisms never stop growing, while other's, like humans, have time clocks in their DNA that tells certain cells to stop reproducing after a certain age. In fact, this only occurs with some cells. Skin and hair cells keep growing, but nerve cells stop, which will eventually lead to the degradation and death of a human. That is, if disease of other agents do not kill you first. Wasn't that a cheerful thing to read.;) But hey, next time you see a 200 year old tree, you'll understand why.

[Mark]

I'd go into why sexual reproduction benefits corals, but this forum is called Reef Central Discussion ,not Reef Central Lecture. My girlfriend says I talk too much already.:D So let's have some more discussion because I enjoy refreshing topics like this. I'm getting a little tired with "what kind of lights are best" threads. Don't get me wrong, I love helping with newbie questions. But sometimes digging a little deeper is fun too.

[capman]

Eukaryotes have an enzyme called telomerase, which, in short, plays a critical role in maintaining the telomeres. Without this enzyme, the telomeres would otherwise be shortened with each replication of the linear eukayrotic DNA. In organisms such as the ciliate Tetrahymena, where telomerase was first studied, this enzyme is always produced and active, generation after generation. In humans and many other animals, however, telomerase activity is only retained in the germ line, while somatic cells (i.e. body cells) lack telomerase activity. However, just because mammals work this way it doesn't mean all other animals or other eukaryotes necessarily need to. In eukaryotic organisms that are are fundamentally immortal (e.g. many cnidarians, some plants, and many others that are immortal barring catastophic events), my guess is that telomerase activity is probably not lost in any cell lines.

[jsfakianos]

Well well, I'm glad some people are interested in this topic. Every once in a while, I am impressed with the broad and complete knowledge of this group.

Just as a note, I thought I read that telomerase is a reverse transcriptase that is acutually expressed in most every cell (expression levels vary dramatically). There was a lot of interest in the telomerase as a cure for aging and an anti-cancer drug target. I remember that constitutive expression of telomerase in an otherwise mortal cell line did indeed immortalize the cell line. However, I think they defined the uncontrollable growth as cancerous. I'll have to look back at the paper, but it turned out that telomerase wasn't really a good drug target either.

I'll be interested to look at the;
"telomeric analysis, X. elongata would probably be an excellent choice, as it can be grown out in large amounts with minimal effort."

This sounds like a good science project for my son. I had originally thought it would also be interesting to try to see what makes Xenia pulse by assaying the pulsing in a spectrum of conditions. I am hoping it would be as easy as pH or oxygen concentration versus carbon dioxide. I thought that it was a way of creating micro circulation to stir out the un-needed by products of the zooxanthallae.



On to the subject....

I first had this idea because of the wine. I remembered a friend was looking at my Xenia and mentioned that corals don't live forever. He said they would grow and grow and grow, then one day, they would die. Why the hell was this supposed to be true. I don't know, but it got me thinking. Do corals live forever. Nothing else does. Why should they be so special.

They may and probably do have longer life spans than our short 75 years. However, a turtle born on the same day I was will outlive me, but that's not forever.

I am not sure that a VW size coral :tongue2: necessarily means that it is centuries old. I suppose it could just be a coral that grows that big. Remember how big them dinosaurs used to get?

Mark, we all here because our wives and girlfriends are tired of hearing our coralrethic theories. Please type out your theories of coral reproduction until your fingers are raw. I'll read it. I love lectures.


I would love it if someone had any information on hand regarding coral lifespans. That would really be worth reading.

[Mark]

I agree that VW size is not a good way to judge age, as many Acropora thickets get quite huge very quickly. But I believe the brain corals that were this size were actually dated. I think it involved something with driling a core out and carbon dating it or something. I wish I could remember where I read that. The cool thing about the article was that it showed how some corals have growth rings like a tree, and they were able to determine changes in global climate that the coral endured. This is of course going way beyond familiar territory so I dunno much about it...except that the article was pretty neat.:)

[Northern Reef]

jsfakianos--thanks for an interesting topic. I won't claim to be anywhere near knowledgable enough to offer an opinion, but I will say that we touched on this subject this weekend while Ron Shimek was in town to speak to our reef club. I will mark this thread and ask him to comment on it when he gets back home.

What I got out of his remarks is that he feels inbreeding is a real possibility for all the animals we keep, and further reinforces the practice of shipping frags and cuttings back and forth across the country, and world.

BTW, he also said that most hobbyists don't let their corals get big enough (for good reasons) to let their corals reproduce sexually.

[capman]

jsfakianos,

"Just as a note, I thought I read that telomerase..... is acutually expressed in most every cell (expression levels vary dramatically)."

Probably so. Though my comments were lifted pretty much straight out of a genetics text, I wouldn't be at all surprised if the text was oversimplifying. Though my knowlegde of telomerases does not go far beyond what I wrote, I would not be surprised if the shut down of telomerase activity in mammalian somatic cells is less than complete.

"Do corals live forever. Nothing else does. Why should they be so special."

There are plenty of organisms that have no intrinsic biological barriers to immortality that we know of. What eventually kills individuals of such species is not aging and senescence, but rather hazards such as predation, disease, fire, flood, drought, storms, accidents, etc. Many perennial plants that spread via rhizomes are fundamentally immortal, for example. My guess would be that a great many invertebrates and other organisms are as well.

Northern Reef,

"we touched on this subject this weekend while Ron Shimek was in town to speak to our reef club. I will mark this thread and ask him to comment on it when he gets back home. .... What I got out of his remarks is that he feels inbreeding is a real possibility for all the animals we keep, and further reinforces the practice of shipping frags and cuttings back and forth across the country, and world."

Inbreeding is sort of a different issue from the "planned obsolescence" that many organisms have built into their body cells, which causes some organisms to age.

I would agree though that inbreeding is potentially a huge problem for anything that reproduces sexually in our systems. Inbreeding results in a loss of genetic variability both within populations and within individuals (a biologist would refer to this "loss of genetic variability within individuals" as a decrease in heterozygosity, or equivalently, an increase in homozygosity), and this can have serious consequences both for populations and for the individuals within those populations.

However, inbreeding is not an issue when we are dealing with asexual reproduction. With asexual reproduction of the sort that is taking place when we fragment a coral, the offspring normally has the same genetic makeup as the parent (unless the original colony is a genetic mosaic due to somatic mutations - there is precedent for this in plants - but this is another story that we don't need to get into here).

I think shipping frags back and forth is a very useful thing to do for other reasons. For example, frequent "dispersal and colonization of new sites" (i.e. transporting and establishing frags of a given coral in other people's aquaria) reduces the chances of a given genetically unique clone going extinct in the event of a disaster in any one of those sites. However, unless home aquarists start to routinely propagate their corals via sexual reproduction, shipping frags around will have no relevance to the inbreeding issue, basically because inbreeding is not an issue unless we have sexual reproduction taking place.

I would love to elaborate much further on all of these issues, but a broken wrist is making typing laborious, and I have work to finish before I go to bed. Maybe another time.

[SteveN]

Has anyone "spliced" corals together. Taking cuttings of the same species from a different colony and putting them together. I know it has been done with flowers. It seems that this might address the concern of telomeric degeneration, at least to this ignorant man:). I don't know diddly about genetics, but this seems like a reasonable question.

[watsonj]

There was a recent study in the pacific that looked a coral fragments on the reef from storm damage. The scientist involved came to the conclusion that fraged corals are unable to repoduce sexually and only sexualy fertalized and settled spores are ever able to sexually repoduce I will look for the link and post soon.
Jon

[jsfakianos]

Cool stuff. Why would frags lose the ability to reproduce sexually? :confused: That is a question for the extremely curious.

Capman, since your hurt, I'll take you on. :p Just joking. I completely agree with you that it would be very difficult to measure a coral's life span in the mist of pollution, unyielding weather, inhospitable aquariums, and any other risky behavior that may go on down there. However, I disagree with you on the immortality of so many organisms. Set aside the orchids that I was too lazy to bring inside when the temperature went below freezing... Most orchids (perennial plants) do indeed live a very long time and reporduce via spreading of their rhizomes. As a biology professor, you will probably tell me I'm wrong with a very good example, but by using the example of perennial plants, you encompassed flowering organisms. I thought flowering plants evolved elaborate mechanisms for sexual reproduction. The orchids are most interesting because they have the 'trap door' that springs and cover the greedy insect with pollen. These plants may be as interesting as corals. Anybody with a desire for interesting organism should take a look.

My point is that although an organism, like corals, may possess the ability to reproduce asexually, we musn't assume that it is beneficial for the coral to continuously reproduce via this mechanism. In fact, I think that it is necessary for the organism to sexually reproduce.


Let's name the most obvious reason. Genetic variation. This will be important for our corals as we add new organisms such as corals or live rock. A friend of mine studies bacteria phages (viruses). He showed me an older paper that measured the phage titer (how much virus) was in a sample of sea water. The number was barely comprehensible :eek: . It was near titers we achieve by present phage culture technigues. The point? Live rock brings in more than beneficial bacteria. Live rock also brings in viruses :( . It may require the variation that can only be brought about by sexual reproduction, or luck, for captive corals to survive many new additions.


I think that I would be very interested in the 'ring' study, or the carbon dating. How long can I expect my new SPS coral to live if I can achieve water quality like a natural reef :smokin: ? Come on Mark, you are sitting on a part of the answer. Where is this golden article that you speak of? Scan it man, scan it.

[saltshop]

Originally posted by watsonj
There was a recent study in the pacific that looked a coral fragments on the reef from storm damage. The scientist involved came to the conclusion that fraged corals are unable to repoduce sexually and only sexualy fertalized and settled spores are ever able to sexually repoduce I will look for the link and post soon.
Jon

Jon,

Just curious if you are referring to the article by Zakai, Levy,and Chadwick-Furman Coral Reefs Volume 19 Issue 2 (2000) pp 185-188 "Experimental fragmentation reduces sexual reproductive output by the reef-building coral Pocillopora damicornis" ?

The article dealt with the affects of fragmentation on sexual reproduction, although it never concluded that coral fragments are unable to "ever" reproduce sexually. It mentions a decreased planulae release rate of both the fragment and the damaged colony due to the decrease in the gross amount of reproductive tissue. Which goes along with what Larry mentioned in the conversation with Dr. Ron that corals must be of a certain size in order to reproduce sexually. I can see that relatively small fragments will not release planulae, but I would be interested to see the information that says that once the fragments grow to a suitable size that they are still unable to sexually reproduce.

[Mark]

I wish I could scan that article:D But I can't remember where I read it. When I was in college waaayyy back in 1999;), I used to kill time between classes and read a lot of cool papers on coral studies in the library(University of Colorado). That's where I read the age sampling thing, I believe. I miss having access to scientific papers like that. There was this one paper by Jong or Yong that described how the "eyes" of a tridacnid clam work. Understanding things like that made the whole reefkeeping experience much cooler. I made photocopies of many articles I liked or used for research, but I'm worried they got thrown out during my last move. I'll have to do some digging tonight in my closet.:)

[sod]

from what i understant is that asexual is for localized spreading and sexual is for long distant and golbal spereading.sexual reproducting is so a successful coral can try and concor another reef faraway. I dont have much knowledge about the biology of coral because i am at high school now and my biology teacher was a tree fanatic, but i think that a coral can live indefently as long as no outside force harms it "perfect conditions" i even read that a bare coral skeleton can grow back to its origonal self. i dont know if you would consisder this a new coral or not.

[capman]

"I completely agree with you that it would be very difficult to measure a coral's life span in the mist of pollution, unyielding weather, inhospitable aquariums, and any other risky behavior that may go on down there".

I also would agree that determining maximum lifespans is difficult, but I don't think I ever said this in my previous post.

"However, I disagree with you on the immortality of so many organisms. Set aside the orchids that I was too lazy to bring inside when the temperature went below freezing... Most orchids (perennial plants) do indeed live a very long time and reporduce via spreading of their rhizomes"

The original issue was whether corals have a built in time clock that kills them after a certain number of cell divisions (e.g. due to shortening of telomeres with each round of DNA replication in their linear DNA). There are many many eukaryotes (corals probably included) that don't seem to have any *intrinsic* biological barrier to living forever, assuming conditions remain healthy and stable forever. That is, many organisms appear to have no built in time clock that shuts them down at some point. Assuming corals fall into this category of organisms, we have nothing to fear from repeated asexual propagation of our corals, generation after asexually propagated generation.

"by using the example of perennial plants, you encompassed flowering organisms. I thought flowering plants evolved elaborate mechanisms for sexual reproduction."

Just because an organism can and/or frequently does reproduce sexually, that doesn't mean that the individuals of that species are necessarily programmed to senesce as they age. Most eukaryotes have some form of sexual reproduction, even species whose individuals seem to have no intrinsic barrier to immortality.


"My point is that although an organism, like corals, may possess the ability to reproduce asexually, we musn't assume that it is beneficial for the coral to continuously reproduce via this mechanism. In fact, I think that it is necessary for the organism to sexually reproduce."

Yes and no. Your initial point was that shortening of telomeres would kill them off in time. As stated above, I really doubt that is the case. This is not to say that there are not benefits to sexual reproduction (there certainly are...see below). All I'm saying is that for many organisms, I really doubt sexual reproduction is necessary for the prevention of telomere shortening.

"Let's name the most obvious reason. Genetic variation.....<snip>...... It may require the variation that can only be brought about by sexual reproduction, or luck, for captive corals to survive many new additions."

The production of genetic variation is the whole point behind sexual reproduction. Sexual reproduction produces genetically variable offspring, which is a better bet for most organisms in their struggle to have their genes represented in future generations. Producing 100 offspring all with the same genetic makeup is like buying 100 lottery tickets all with the same number. In contrast, producing 100 genetically different offspring is like buying 100 lottery tickets all with different numbers. Given that the conditions and challenges that will be faced by the offspring are unpredictable and variable, producing lots of different genetic combinations increases the chances that at least one of those offspring will, by chance, end up with a winning combination. (If conditions are stable, uniform, and favorable, however, asexual reproducers win hands down, at least in the short run).

If our concern is to maintain the health and vigor of the corals we keep in captivity, I would maintain that repeated sexual reproduction in captivity has the potential of accomplishing just the opposite of what we want, unless the people doing the coral breeding are extremely careful about how they proceed. Repeated mating with close relatives (which *OFTEN* ends up happening in the comparatively small captive populations that constitute the breeding stocks of many of the animals and plants humans breed in captivity) generally results in a loss in genetic variability at the population level, and a reduction in heterozygosity at the individual level. The more rounds of sexual reproduction a small population goes through, the worse this situation becomes. Ultimately, we end up with highly homozygous breeding lines, at which point many of the original genes that were present in the original population taken from the wild will have gone extinct from our breeding lines. If conditions change, or a new disease is introduced, the consequences might be more devastating for such a uniform, inbred population than for a captive population consisting of multiple genetically different clones of wild-collected and presumably naturally outbred and highly heterozygous corals.

This is not to say that it would not be incredibly cool to get to the point where we can routinely have sexual reproduction of our corals taking place in captivity. Sexual reproduction would facilitate, among other things, breeding for desireable characteristics (e.g. color, growth form, hardiness, disease resistance, etc), as well as faster, larger scale production of new colonies.

Routine sexual reproduction in captivity is NOT likely to promote greater genetic diversity in our captive populations though. I would maintain that for organisms that can be propagated asexually, asexual reproduction is the best way to preserve genetic diversity and wild-adapted genotypes in captivity. I wish it were possible to do this with my freshwater angelfish, killifish, and wild species of bettas I breed at home...the genetic quality of the breeding lines of many freshwater fish species can very easily deteriorate with multiple generations of captive breeding. I suspect that we'll also be seeing this very soon in captive-bred populations of Bangaii cardinals and other captive bred marine fish fairly soon unless breeders are very dilligent about maintaining large breeding populations and avoiding inbreeding.

[jsfakianos]

Hmmm... Right-O. Aquarist aren't ready to reproduce the genetic diversity found on a reef. Not by sexual reproduction or any other means. I hope I didn't imply that they were?

I hope you don't mind if I more clearly ask you (capman) to elaborate on one of your comments?

I suppose we wouldn't be too far off topic (Does a clonal population of corals have an intrinsic clock?) if we were to allow you to elaborate on some of your immortal organisms. I'm sorry, the elusive and rare immortal rhizomic organism ain't holdin' water.

Since there are so "many" of these immortal organisms, please allow me to ask you to focus your example organism further past the category of eukaryotes. Perhaps you could describe an immortal organism in the Animal kingdom. If there are also "many" within this taxonomic category, please go one step better, give us an example in the phylum Cnidaria.

A convincing answer would indeed be impressive. Perhaps as impressive as the description of telomere's ugly sister, reverse transcriptase. The description of that beast won a Nobel prize. Good luck.






I still think Sculpin's telomeric analysis and Mark's carbon dating are going to give the best evidence for or against my far-fetched telomeric depletion hypothesis.

Until those assays are completed, very little can be added to this thread. However, let's post a "Who thinks they know science?: II" Any crazy ideas out there?

[capman]

"I suppose we wouldn't be too far off topic (Does a clonal population of corals have an intrinsic clock?) if we were to allow you to elaborate on some of your immortal organisms. I'm sorry, the elusive and rare immortal rhizomic organism ain't holdin' water."

A substantial proportion of the plant kingdom is capable of reproducing asexually, generation after generation after generation with no loss in vigor or viability that I am aware of. The the orchids you mentioned previously that spread via rhizomes are just the tip of the iceberg. Strawberries and raspberries (clones of which might lose vigor due to aquiring viruses by the way, not because of aging) are examples. Many lawn grasses and prairie grasses are examples. Daylillies are common examples (incidentally, the most commonly encountered "wild" daylily, is a sterile triploid form of Hemerocallis fulva...these things spread like crazy and are vigorous as can be after many many years of exclusively asexual reproduction). Sugarcane is normally propagated by asexual reproduction. Every Yellow Delicious apple tree is descended, as I understand it, from one single tree owned by Stark Brother's in Missouri, and propagated for many years by asexual reproduction. Ditto for red delicious. Navel orange trees produce no seeds, but have been around for many years, propagated asexually. I have not heard that Navel orange growers are about to face a crisis due to the senescence of all of their trees all at once due to a lack of sexual reproduction for many years. I have neither interest nor time to elaborate further on these plant examples, but suffice it to say that such examples are anything but rare and elusive. They are all around you.

I have no doubt at all that the chicken liver sponges creeping about in my seagrass tank, dividing into multiple colonies as they do so, are capable of doing this indefinitely if conditions remain suitable. Ditto for many other sponges. Some sea cucumbers reproduce asexually by dividing in two. Ditto for certain sea stars and brittle stars that do this routinely in my tanks. The list of likely animal examples could be expanded much further than this.

As for the supposed necessity for sexual reproduction: See the plant examples above that contradict this idea. Also, many unicellular eukaryotes appear to be able to reproduce asexually indefinitely, if conditions stay good (most are also capable of sexual reproduction). Also there are many examples of crustaceans and insects and other inverts that can reproduce asexually as long as conditions remain good (Daphnia and Aphids come to mind....no, these are not necessarily examples of immortal individuals, but rather examples of how sexual reproduction is not always necessary).

Are any, or many, cnidarians fundamentally immortal? Conventional wisdom seems to say yes, and I see no reason to seriously doubt that this is true for quite a few species. I have not personally read any scientific studies involving corals in the primary literature that have backed up this hypothesis (I have not actually looked for them though), but the idea seems very feasible to me, and there is precedent for lack of programmed aging and senescence in many other organisms. If you have or know of data to the contrary, we would all love to hear about it. (However, going back to your initial example of Xenia stands crashing in reef systems, I think there are plenty of other very feasible explanations for such crashes besides lack of sexual reproduction).

I have no interest in beating this topic into the ground any further.