Marine food triggering metamorphosis?

[Daniel]

Hi,

I have got a question I could not find an answer to although I searched the Internet and several papers on metamorphosis in axolotls.
In another (german) forum there is a rumor abroad that feeding an axolol with marine food (pieces of fish, shrimps, mussel etc.) may cause it to morph because of the iodine contained in this food.

As far as I know until now it is necessary to use several hormones to induce a metamorphosis and not just to feed them some iodine but I am not quite sure about it. Maybe someone of the members here could help me out with some information or even a paper looking into that topic.

And to make it clear from the start: I don't want to morph one of my axolotls, I want to prevent it. But I don't like baseless rumors neither

Thanks for your answers,

Daniel

 

[ryanhearps145]

Hello, metamorphais is a difficult topic, it is only normally done in labratories so it is very hard to get information. The only real way to is to ask someone who has experienced it. Hormones are given to the axolotl to cause morphing but it is said that iodine may cause this, I certainly wouldn't think mere seafood would contain enough iodine to have any affect but I would recommend if at all possible you would be better to feed them on non-marine food if you are worried.

How much water is in the tank and are you allowing them to be able to climb above water as this can also promt mutation. Morphing is very stressful and dangerous to axolotls so be careful and I wish you all the best.

 

[Daniel]

Hi,

it is not too hard to get information on metamorphosis (I am working at a university and so I read many of the papers published so far) but all the studies I know are dealing with hormomes.
What I know is that iodine is necessary to complete a metamorphosis (there are neotenic salamanders that do not metamorphose because of too low a level of iodine).

But the interesting fact for me is wether iodine itself can push axolotls into metamorphosis (I know that they certainly won't be able to complete it) or not.

I don't want to try to morph an axolotl I like them in der neotenic shape quite well. I am just curious wether these rumors are myth or fact.
This "iodine may trigger axolotl to metamorph" - rumor does not only cover feeding, but salt baths as well. John writes on his "Health"-page that iodized salt can be used for a salt bath. In contrast here (what means in this other forum) it is said that only salt without iodine should be used.

Greetings, Daniel

 

[Jennewt]

It's a very interesting question, Daniel. I don't know if there is a definite answer. I think people say to avoid marine foods and iodized salt as a kind of common-sense precaution. "Better safe than sorry." I don't think there is any clear scientific knowledge as the basis for these recommendations.

Somewhere in the archives of scientific literature, there was probably a titration experiment to find the exact concentration of iodine needed to cause metamorphosis in an axolotl. And we can probably find out the amount of iodine in marine foods and salt. However, this would require some serious research! (Additionally, there could be complications regarding the chemical form of the iodine; some forms may be more potent than others.) If anyone can find these pieces of information, I'd be happy to post the information somewhere permanent on Caudata.org.

 

[Ed]

The iodine content of sea food tends to be very variable both within and between species and individuals (for example see http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed&list_uids=11767171&cmd=Retrieve&indexed=google ). I suspect (and am too tired to go digging (but John may know something about dietary levels of iodine triggering metamorphosis) that the levels of iodine in the seafood are probably too small to really affect most axolotls. I suspect that the ones that do metamorph when fed small amounts of iodone containing foods may be from the lines that were crossed with A. tigrinum and if I remember correctly, axolotls do produce some levels of thyroxine but there appears to be something that prevents metamorphosis at the levels present in the body of the axolotl (see www.ijdb.ehu.es/web/contents.php?vol=40&issue=4&doi=8877439 for a decent discussion on it) . If I remember correctly, it takes a good dose of iodine as long term exposure to small amounts doesn't trigger it in axolotls. (also note that if I remember correctly bromine (see http://www.springerlink.com/content/j445kv1179358791/ for the abstract) can also trigger metamorphosis in amphibians if dosed at sufficient levels)

Also it isn't correct to say that axolotls do not normally undergo any metamorphosis as they apparently do undergo a cryptic metamorphosis (see Tompkins, Robert; 1978, Genie control of axolotl metamorphosis; American Zoologist 1978 18(2):313-319 (abstract at http://icb.oxfordjournals.org/cgi/content/abstract/18/2/313 (I thought I had remembered seeing something on it..)

Some rambling tired and probably useless comments.

Ed

 

[Daniel]

Thanks for your answers, the comments aren't useless at all (and I may so some more research by myself)!
The "better safe than sorry"-way is just the way I practice it (by actually not feeding any marine food) but I am still curious if there are any statistics about a rate of metamorphosis.
As far as I remember (and I hope not to mingle different papers) there was also a passage in "Developmental biology of the axolotl" describing a slight increase in the numbers of "spontaneous" metamorphoses at the Indiana colony when they started feeding pelletfood - and at least these pellets are containing a high amount of marine fish and also some level of iodine (I asked a german producer about it).
I will have a look into the links provided by Ed, thank you so far!

Daniel

edit: found the passage in "Developmental Biology...": Page 224 - and it was Ottawa, not Indiana Colony. Armstrong et al give no explanation as to why the rate of metamorphosis was slightly higer with salmon pellets

 

[Ed]

Hi Daniel,

I am going to begin and end this paragraph with the following statements... I am including a lot of qualifiers here as I am speculating and do not want to continue, start or otherwise support or fuel and anecdotal debate that may or maynot be true.

The problem with the quote is that there is no distinction to the axolotl line in use. If the line is one of the ones derived from the A. tigrinum x A. mexicanum hybridization experiments then it is possible that the level of iodine was sufficient to trigger metamorphosis in those animals while others were not affected.
I would also consider that as the pellets are made from whole fish (which is actually a better food source than pieces of meat or fish) that the forms of hormones affecting metamorphosis may be contained in the pellet as I do not now how stable they would be through processing and are a more potent metamorphic trigger for those axolotls that can undergo metamorphosis. (see http://www.pnas.org/cgi/reprint/94/24/13011.pdf?ck=nck for some discussion on it).
Instead of the iodine concentration, it maybe the actual hormones themselves inducing some metamorphosis in susceptiable animals (this could be dependent on the part of the fish being fed to the axolotls (for example, offering a lot of small fish heads..).
I am including a lot of qualifiers here as I am speculating and do not want to continue, start or otherwise support or fuel a debate that may or maynot be true. I suspect this occurs only to a very small minority of susceptiable animals and that people maybe linking it to sea food as opposed to determining if the axolotls came from the hybrid line which if they get both of the genes for metamorphosis can spontaneously metamorp...

Some precaffiene (awake) comments....

 

[Daniel]

Hi Ed,

nice statement...should be used more often in my opinion.

As for the lineage of axolotls: Well, I am from Germany/Old Europe and I am sure that there are nearly no "pure" axolotls left, at least not in the pet-sector - quite the contrary, there have been some new hybridization-experiments lately, pushing up the A. tigrinum part (unfortunately in my opinion they have even been left to hobbyists, nowadays mixing old and new hybrids without control, constraint or any records of breeding).

So there seems to be only one clear answer to my question "Does the feeding of marine food trigger metamorphosis?" and this answer is "Maybe..."

Daniel

 

[Ed]

Hi Daniel,

If there are more tigrinum x mexicanum hybridizations going on then more and more of that population will spontaneously metamorph as tigrinum will supply the needed genes (which are dominate so they will displace the recessives reducing the appearence of neotony).. If that is the case then it won't be long before you don't have axolotls anymore....

Ed

 

[Daniel]

Hi Ed,

I am completely with you at that point and therefore I do not use any of these hybrids for breeding (unfortunately I'm just part of a minority by not breeding with them because the have a weird look).
I only have one of this kind and I do not sell her because I fear that others will use them to get more uncommon colors - sad as it is for the axolotls - genetic pool.
As far as i was told they were "naturally" mated with a neotenic tigersalamander but I do not know if the neoteny of this animal is genetic or facultative.

All the best,
Daniel

 

[Ed]

Hi Daniel,

I would have to say that yes the tigers are providing the proper genes to allow for metamorphosis in the hybrids. This is due to the fact that in A. tigrinum (and other ambystomids) the metamorphosis is facultative and without the enviromental cues, the larva do not metamorph. There are a number of different theories on why it works this way, none of which to my knowledge have been fully excluded. This is where axolotls differ as axolotls are not facultative.

(see http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=dbio.box.4337 )
also see Shaffer HB, Voss SR. (1996). Phylogenetic and mechanistic analysis of a developmentally integrated character complex: alternate life history modes in ambystomatid salamanders. Am. Zool., 36: 24-35.

Voss SR. (1995). Genetic basis of paedomorphosis in the axolotl, Ambystoma mexicanum: a test of the single gene hypothesis. J. Hered., 86: 441-447.

Ed

 

[Daniel]

Thanks Ed,

I have read the papers of Voss some time ago (and to be true - I do not remember them in every detail but found them quite interesting) and I think that the "metamorphosis"-gene - theory supports some observations made by Humphrey in his first cross-"breeding" experiments (you know - creation of the albinos). I think in this case the maths don't fit because there was only a small (but maybe higher as normally) part metamorphosing (as far as I know - I did not do this breeding experiment).

Daniel