Linckia Sea Stars. by Tooen
- Thread starter clyde
- Start date
I agree, very good article. From my studdies I would just like to say that, in Australia anyways, that a colour variant has/can have no effect on the species (as stated), but once there is no-interbreeding between the two colour variants, you have a new speccies. This interbreeding bridge was formed by some specific physical differences.
I would be interested to see what studies/tests were preformed by williams, as well as seeing the selection tech' for the animals selected to do the testing on.
I would be interested to see what studies/tests were preformed by williams, as well as seeing the selection tech' for the animals selected to do the testing on.
The Williams article (S.T. Williams (2000) Species boundaries in the starfish genus Linckia Marine Biology 136:137-148) didn't do any breeding studies at all. Instead the author uses DNA evidence to show that differences between a sample of L. laevigata and L. mulifora are roughly an order of magnitude less (~1.7% sequence divergence) than between any other species pair in the genus Linckia (~7.5 - 22% sequence divergence, depending on the pair being compared). Furthermore, the "species" L. mulitfora nests completely within the L. laevigata clade, such that L. laevigata from Thailand to South Africa are more closely related to L. mulitfora than they are to other L. laevigata found in Guam and throughout the Indo-Pacific.
Thus, either these animals need to be considered a single species (which Williams argues is the case because they appear to exchange genetic information, which is indirect evidence that there is currently, or has been recent interbreeding among these "species"), or there would need to be 3 species, and the seastars currently called L. laevigata would have to be split to reflect the fact that there is more difference between the Guam/Indo-Pacific and the Thailand/South Africa L. laevigata than there is between L. laevigata and L. multifora overall...
Rob
Thus, either these animals need to be considered a single species (which Williams argues is the case because they appear to exchange genetic information, which is indirect evidence that there is currently, or has been recent interbreeding among these "species"), or there would need to be 3 species, and the seastars currently called L. laevigata would have to be split to reflect the fact that there is more difference between the Guam/Indo-Pacific and the Thailand/South Africa L. laevigata than there is between L. laevigata and L. multifora overall...
Rob
A simply breeding study to give numbers of Physical genetic differences would soon prove the other side of things. Since there are 3 basicly the same variants, then they would have a 9,3,3,1 pattern, of say colour pattern, passing. It might be a simple test, but it world give about a 90% confidence in the out come.
Ash
Ash
Not really - it is very hard to hold free-spawning marine invertebrates to Mayr's Biological species concept (which is what you follow here - a species is defined by a group of potentially interbreeding organisms) that most scientists generally support for vertebrates. In the case of free-spawning marine inverts, however, we can often induce fertilization and viable offspring in the lab between two "species" but are then left with the qeustion of whether or not that ever happens in nature (e.g., it takes 10x more sperm in the lab to cross two GBR corals than is measured in the field after the egg bundles break apart).
Alternatively, if we fail to breed these animals successfully in the lab, can we really conclude that they are indeed separate species? The problem is that we fail to breed many more marine organisms in captivity than we have success with, and we know that animals which cannot be bred in the laboratory are reproducing just fine in the wild. Using laboratory breeding experiments makes a difficult metric for whether or not animals are interbreeding, because it may happen only under the special circumstances in the lab, or only at certain times that the researchers did or did not happen to test.
Even if we could do the breeding experiement in a convincing manner, the experiment that you suggest assumes that the traits you would measure, say color variants in this case, are under simple genetic control of one or a few genes, and that there is no biased transmission of traits among individuals, interaction of the few genes of interest with the genetic background in which they find themselves, or strong environmental effects. All of these things have been shown to occur within good Biological Species as well as between them, and could easily mess up the results for the experiment, and pose a real problem for the interpretation of whether or not the breeding experiment supported or rejected the Biological Species concept for these animals. Another bigger problem with marine organisms arises when we try to apply this species concept to obligate asexual organisms. If we define a species as a group of animals that are not capable of interbreeding, then every individual of an asexual "species" must be considered distinct from every other one, because they do not interbreed...
That is why many people have started to move away from this metric for defining a species, and prefer to use indirect genetic evidence for whether or not a given group of animals is interbreeding. If animals are reproducing in the wild (even only rarely), there will not be any consistent genetic differences detected among them, so this really is still using the same basic idea, it just comes at it from a different direction than traditional breeding experiments which suffer from a number of problems such as these that can make applying a species name quite difficult...
Rob
Alternatively, if we fail to breed these animals successfully in the lab, can we really conclude that they are indeed separate species? The problem is that we fail to breed many more marine organisms in captivity than we have success with, and we know that animals which cannot be bred in the laboratory are reproducing just fine in the wild. Using laboratory breeding experiments makes a difficult metric for whether or not animals are interbreeding, because it may happen only under the special circumstances in the lab, or only at certain times that the researchers did or did not happen to test.
Even if we could do the breeding experiement in a convincing manner, the experiment that you suggest assumes that the traits you would measure, say color variants in this case, are under simple genetic control of one or a few genes, and that there is no biased transmission of traits among individuals, interaction of the few genes of interest with the genetic background in which they find themselves, or strong environmental effects. All of these things have been shown to occur within good Biological Species as well as between them, and could easily mess up the results for the experiment, and pose a real problem for the interpretation of whether or not the breeding experiment supported or rejected the Biological Species concept for these animals. Another bigger problem with marine organisms arises when we try to apply this species concept to obligate asexual organisms. If we define a species as a group of animals that are not capable of interbreeding, then every individual of an asexual "species" must be considered distinct from every other one, because they do not interbreed...
That is why many people have started to move away from this metric for defining a species, and prefer to use indirect genetic evidence for whether or not a given group of animals is interbreeding. If animals are reproducing in the wild (even only rarely), there will not be any consistent genetic differences detected among them, so this really is still using the same basic idea, it just comes at it from a different direction than traditional breeding experiments which suffer from a number of problems such as these that can make applying a species name quite difficult...
Rob
I agree that we are moving away from these methods, but they still have there place. there is very little that we actually know (in the whole sceme of things) about genitics. Yes we know alot, but what we know is not enough in the areas we need. This simple experinment, though long and to some degreee hard to interprate (but then agian so was crystalography and mir's) at least in some cases it would give us a better overall indercation of what physical characteristics belong to who/what.
If you were to run this experinment, not only would you have them breed via sex, you would also produce clones (simply cut off feet). I know from other species you can find this Physical difference accour even in clones. If there was a physical change in any of the clones it in itself would prove there is no "multiple species" present in these starfish. One would also have to spend some years collecting all the species (or supposive) they colud find with a small deviation, then start the breeding,in the 3 main forms, clone, physical species-to-species and cross physical species.
Once again, if any of these physical species follow any of the chi-square test, then you can remove them from the collected group.
As with many organisums, the boarder of one species to another is slightly blurred. As for Asexual reproduction, even these organisums still pass genetic information from one to another (hence why we are having problems with antibiotic resistant disease and pesticide resilliant germs).
In alot of species we only have a good indication at best for there species type, but atleast it is an indercation. We don't in the end need a Straigh-down-the-line answer, but if we can do something to move a little closer to the real truth, then......
Ash
As a side to this. I have talk to a freind in Cairns, who works at James Cook uni (yes I know that JC is not in Cairns), and suggested such an experinment to be conducted. He has already started the work on it and hopes to introduce it as part of his second years students criteria next year.
If you were to run this experinment, not only would you have them breed via sex, you would also produce clones (simply cut off feet). I know from other species you can find this Physical difference accour even in clones. If there was a physical change in any of the clones it in itself would prove there is no "multiple species" present in these starfish. One would also have to spend some years collecting all the species (or supposive) they colud find with a small deviation, then start the breeding,in the 3 main forms, clone, physical species-to-species and cross physical species.
Once again, if any of these physical species follow any of the chi-square test, then you can remove them from the collected group.
As with many organisums, the boarder of one species to another is slightly blurred. As for Asexual reproduction, even these organisums still pass genetic information from one to another (hence why we are having problems with antibiotic resistant disease and pesticide resilliant germs).
In alot of species we only have a good indication at best for there species type, but atleast it is an indercation. We don't in the end need a Straigh-down-the-line answer, but if we can do something to move a little closer to the real truth, then......
Ash
As a side to this. I have talk to a freind in Cairns, who works at James Cook uni (yes I know that JC is not in Cairns), and suggested such an experinment to be conducted. He has already started the work on it and hopes to introduce it as part of his second years students criteria next year.
rob,
i´ve had my blue lynchia for about a week. it´s with some small white points in the body. what could be? in the same day i bought it, a friend of mine gave me an atlantic sea star, which i don´t know the species. after 2 days, it appeared with a white spot in it´s body and in the next day, the local was looking like dissolved. i take it of the tank and put it in a small bowl for 2 days. after this period, it was fully recovered so today, i put it back into the tank. i think the lynchia star is with the same thing that this atlantic star had. would you have any idea about it?
i´ve had my blue lynchia for about a week. it´s with some small white points in the body. what could be? in the same day i bought it, a friend of mine gave me an atlantic sea star, which i don´t know the species. after 2 days, it appeared with a white spot in it´s body and in the next day, the local was looking like dissolved. i take it of the tank and put it in a small bowl for 2 days. after this period, it was fully recovered so today, i put it back into the tank. i think the lynchia star is with the same thing that this atlantic star had. would you have any idea about it?
Eduardo, it is very hard to say what the tiny white spots that you see appearing on your star are from here. Hopefully it is not the result of dead tissue appearing from an osmotic shock, but the area that went from a while patch to "looking dissolved" sure sounds that way. Given that both of your stars have shown signs of it within a short period of time, it may be that they went through the same salinity change or other osmotic shock a few weeks ago. Were they introduced at the same time, or did your tank go through a large salinity change about then?
Osmotic shock is more of an issue for some stars than others. Many intertidal stars do not seem to suffer greatly from salinity changes, but subtidal stars often have this problem. Even among the subtidal stars, some seem able to lose a small portion to the shock, but recover on their own if left alone (such as it sounds that your unidentified Atlantic star has). Others, such as the blue Linckia do not seem so fortunate. For what ever reason, blue Linckia seem to be particularly sensitive to osmotic shock, and they often start to show these white patches of necrotic tissue a few weeks after their exposure. Frequently these white patches spread rapidly as the star begins to dissolve and soon dies. Unlike your Atlantic star, I have not heard of any cases of a Linckia which had begun to dissolve spontaneously recovering. Sadly, once a Linckia starts to dissolve, it is usally the beginning of the end for these beautiful animals.
In terms of treatment, many have been proposed, but none seem to work in even the majority of cases, and so the jury is still out on what to do about this event should you encounter it in your tank. The only uniformly useful treatment seems to be prevention -- make sure you do not shock your animal when transporting it or doing water changes, etc. Some people have reported success by amputating the effected area of the star and allowing the rest to recover. Again, this is unpredictable in its success, and some people feel that this rough treatment simply sped the inevitable and pushed the star over the edge, causing it to die more quickly. However, others argue that if there is any chance of saving the star, it is worth the risk, and this is one possibility. Iodine dips and various other treatments have been tried with about the same rate of failure - there is still no good answer for you in terms of what to do.
If you decide to amputate, there is a nice set of pictures by GobyGirl on her amputation of an arm from her Linckia with the patrasitic snail Thyca embedded in it online here, and some follow up on the subsequent recovery of the star here. If you decide that is a little drastic for you, then you may as well try your isolation in a bowl technique. Perhaps the star will recover, and if my guess is right about the cause, then you have nothing to lose by trying...
Good luck,
Rob
Osmotic shock is more of an issue for some stars than others. Many intertidal stars do not seem to suffer greatly from salinity changes, but subtidal stars often have this problem. Even among the subtidal stars, some seem able to lose a small portion to the shock, but recover on their own if left alone (such as it sounds that your unidentified Atlantic star has). Others, such as the blue Linckia do not seem so fortunate. For what ever reason, blue Linckia seem to be particularly sensitive to osmotic shock, and they often start to show these white patches of necrotic tissue a few weeks after their exposure. Frequently these white patches spread rapidly as the star begins to dissolve and soon dies. Unlike your Atlantic star, I have not heard of any cases of a Linckia which had begun to dissolve spontaneously recovering. Sadly, once a Linckia starts to dissolve, it is usally the beginning of the end for these beautiful animals.
In terms of treatment, many have been proposed, but none seem to work in even the majority of cases, and so the jury is still out on what to do about this event should you encounter it in your tank. The only uniformly useful treatment seems to be prevention -- make sure you do not shock your animal when transporting it or doing water changes, etc. Some people have reported success by amputating the effected area of the star and allowing the rest to recover. Again, this is unpredictable in its success, and some people feel that this rough treatment simply sped the inevitable and pushed the star over the edge, causing it to die more quickly. However, others argue that if there is any chance of saving the star, it is worth the risk, and this is one possibility. Iodine dips and various other treatments have been tried with about the same rate of failure - there is still no good answer for you in terms of what to do.
If you decide to amputate, there is a nice set of pictures by GobyGirl on her amputation of an arm from her Linckia with the patrasitic snail Thyca embedded in it online here, and some follow up on the subsequent recovery of the star here. If you decide that is a little drastic for you, then you may as well try your isolation in a bowl technique. Perhaps the star will recover, and if my guess is right about the cause, then you have nothing to lose by trying...
Good luck,
Rob
rob,
thanks for the reply. now i can´t see how the star is going because it´s on the back of the tank. i do see 4 of its 5 legs and all are fine, without any white spots. but there is still one i can´t see and it can be injured. as soon as i can see it all, i´ll tell you how the situation is going. thanks
thanks for the reply. now i can´t see how the star is going because it´s on the back of the tank. i do see 4 of its 5 legs and all are fine, without any white spots. but there is still one i can´t see and it can be injured. as soon as i can see it all, i´ll tell you how the situation is going. thanks
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