Inducing Neoteny

Nowicki418

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Wow, finally. I've been researching this for months and I think Caudata.org may finally have the experts I've been looking for!

For an independent study in High school I really want to do an experiment on neoteny in larval tiger salamanders (Ambystoma tigrinum tigrinum). I will get the larvae from a pair I am in the process of breeding.

Although I may end up just doing an activity on causing a temporary state of neoteny, My real goal is to raise sexually mature neotenic adults ( which could be easily bred ). The experiment is still under work but here is the basics of what I am planning.

  • Three different 20 gallon tanks
  • Each tank holds four larval salamanders ( the age in which the larvae will be separated for this experiment is to be determined )
  • Each tank receives an activated carbon filter to remove iodine from the water
  • Each tank is equipped with a water chiller and maintained at 10 degrees Celsius.
  • One tank acts as a control group
  • The other two receive a different amount of a hormonal influencing treatment.
I don't know what the "hormonal influencing treatment" is going to be yet. As I have been researching salamander endocrinology for some time now I'm not going to go into the specifics. I know that the thyroid hormones are a major contributor in causing the climax stages of metamorphosis. Of the thyroid hormones thyroxin is one of the big ones. One of my theories is to remove as much iodine from the salamanders environment so they are unable to produce thyroxin. However this could have other side effects I don't want to risk.

My new lead is to inhibit the interpretation of thyroxin and other important hormones. I believe prolactin is a hormone that counters the effects of thyroid hormones. But how would I increase prolactin levels? What other side effects could this cause?

One of the things I fear is that I will have to continue giving the salamanders a special treatment for there entire lives or they would transform. Perhaps by breeding these sustained neotenes I could breed them many many times until a gene for permanent neoteny is isolated. They are closly related to A. mexicanum after all!

It is possible, but not necessarily easy. Despite becoming a senior in high school and being new to this website I really know my stuff. But digging for information through the internet and college textbooks can be slow work.
 

Azhael

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I don´t think removing iodine from the environment is going to have much of an impact, if at all, since they will be receiving iodine from their diet.
Are the parents neotenic? If so, their offspring will inherit the predisposition to remaining neotenic under the right conditions. If the parents are not, your chances of inducing neoteny on their offspring are very slim indeed. Very low densities, cool temps, deep water and abundant food are the factors that might induce neoteny.

I´d personally discourage you from selecting offspring for neoteny if you succeed in breeding them for several generations, as you have no way of knowing which other traits you are selecting for, and those could be very undesirable. Many people disagree, but my personal opinion is that artifitial selection only causes problems (to the animals, certainly not to people´s wallets).
 

Nowicki418

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Well removing iodine from the environment is just a side effect of installing a filter. They don’t need much iodine to make those hormones and it is unlikely that I could completely cut off the source. ( not to mention the consequences of a depletion of iodine ) And no, the parents are not neotenic. I’ve never even seen a neotenic tiger salamander before. As I said before I probably will only postpone metamorphosis but the real goal is sexually mature larva. The key has something to do with regulatory hormones but I’m still trying to figure out what. Does anyone out there have any knowledge of the salamander endocrine system?

By the way I don’t have the time or resources to selectively breed. Just an idea, and I thought it could help gain insight into axolotl phylogeny.
 

Azhael

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Not to spoil your plans, but if you have normal adults, breeding them is going to be very difficult. Very few people ever succeed, chances are not good. Good luck, though, i hope you do succeed.
 

Nowicki418

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Well the experiment aside. Neoteny is still an interesting topic and I want to know the details.

By the way, I know believe that neoteny is caused in the wild by a gland not doing what it is supposed to. If this is caused genetically then it is impossible to raise neotenic individuals. But I still believe that environmental factors can cause it. Any thaughts?
 

Nowicki418

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The more I look into this the more it seems that neoteny is caused by environmental factors. Although the breeding of neotenic salamanders may cause a genetic race, such as the axolotl, I do not belive this is how it begins.

Neotenic tiger salamanders seem to be a rare occurance. There also seems to be a trend where neotenic populations are located. If neoteny was caused by a faulty gland gene then you would see the mutation occur all over the place not just in a few areas.

I also have a new lead ( in addition to interfering with the interperetation of thyroid hormones ). Rather than prevent "growth horomones" from being recognized I increase the level of growth hormones myself. If this were done in to a salamander that has reached the age where it is capable of changing but cannot due to a cold temperatures, I believe it may cause incomplete metamorphosis. There wouldn't be enough hormone to cause a complete change but it would be enough to cause them to become sexually mature.

I kind of realize now that the information I was hoping to recieve through this post is something only a Herpetologist would know as I am trying to find advanced information on the physiology behind metamorphosis. I would like to state again that I do not expect to raise neotenic salamanders, only that through this it will give me a great backround on the subject and help me gain experience on how to put a formal experiment together. If raising neotenic salamanders was practical I'm sure hobbyists would already know how to do it.

By the way, even if I am unable to breed tigers myself I am still willing to look elsewhere for them, ( Only need 4 or 6 ) I'd also like to remind readers that I'm still looking into ideas for an independent vairable.
 

Azhael

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If neoteny was caused by a faulty gland gene then you would see the mutation occur all over the place not just in a few areas.

Why?

A mutation affecting hormonal expression or sensitivity and causing physiological consequences is certainly possible but is an exception, it´s not, largely, how caudate neoteny works at all.
Neoteny is caused by genetic factors under certain environmental pressures and conditions. Both are critical. You can´t have neoteny without the genetic and physiological mechanisms that control development, and you can´t have neoteny if the environment is clearly selecting against it. Most tiger salamanders are not neotenic because they inhabit water masses which select for non-neotenic behaviour. When conditions permit, or select for neoteny, then populations can easily adapt to that because the underlying physiological mechanisms are already there. It´s called facultative neoteny. It´s only expressed under a particular set of conditions, some of which i mentioned in the previous response. Recreating those conditions in captivity is very difficult.
The environment provides a set of conditions, those conditions affect the hormonal levels and that in turn has an effect on physiology.
When conditions are selecting for neoteny for many generations, it´s possible that the mechanisms become more or less fixed to different degrees and what you get is obligate neoteny as is the case of axolotls.

Injecting hormones alone may or may not work. Forcing metamorphosis in obligate neotenic animals like axolotls, generally causes problems (reduced life-span, deformities, etc..). Forcing an hormonal invalance that prevents physiological development in an otherwise "normal" individual may well have very similar consequences.
 
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Nowicki418

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This is exactly what I mean when I say research is slow. The stuff I read before usually talked about mutations causing neoteny or environmental conditions causing it, not both. Azhael, you seem to know a lot about this and I'm glad you’re returning to post on here.

When I said that the information on metamorphosis regulating hormones was something only a Herpetologist would know, I meant myself included. Influencing things on a hormonal level is beyond my level. It is far more complex than I originally realized. But even saying that, I am not aborting things completely. Neotenic individuals occur in different kinds of water than the traditional vernal pools (obviously). So why not design something that compares growth in a vernal pool and growth in a permanent body of water. As I said in the first post, this is for an experiment at school, not an attempt to raise neotenic tigers ( which wouldn’t make great pets if that’s what you thought ) It will most likely concentrate on pH, water level, temperature, density, and dissolved oxygen. With this design it would also not have to be salamander larvae, tadpoles could also be used.

The other option is to see what the effects of brumation are on developing larvae ( Caudate and Anuran ). Essentially it would be raising a batch normally and putting another through brumation. Then comparing to see if there are any differences.

Do either of these seem like a better idea than “Inducing Neoteny”? If so which one do you like better?

( On a side note: I did read about a large pond that is because of its geography receives low temperatures. Tiger salamanders are known to take three or four years to change into adults in this area. Although the text referred to this as neoteny the larvae were not sexually mature. Fascinating isn't it? Even with all that time something else is needed to cause sexual maturity in larvae. )
 

Azhael

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Well, let me assure you that i don´t know that much xD But I´m happy to contribute with what i know.
It is problematic finding reliable sources of information, there´s so much out there and most of it is incorrect to different degrees...But you are on the right track! Researching extensively and not taking the first answer you are offered is a wise choice, hehe.

Let me say i think it´s FANTASTIC that you are curious and you want to investigate and experiment, i really think it´s a wonderful thing :)

Personally i think a study about the characteristics of the aquatic environments that this species (or others) inhabits is a much more realistic subject and it would actually be very helpful information. The subject of the effects of brumation on larvae is also an equally interesting topic. Choose that which you find more practical for you or more interesting.
The problem with the subject of induced neoteny is that i sincerely think it´s unrealistic for your situation and the species of choice is not the best candidate, that´s why i raised some objections, nothing more.

Actually, many people would love to have neotenic tiger salamanders! Aquatic animals are generally consider easier to keep and feed. Neotenic individuals are sought after, specially since they are far easier to breed than terrestrial adults. Neotenic tiger salamanders are essentially the same as axolotls and people go crazy for those xD

About the last comment. It sucks that the media gets those things wrong, but hey, most people are grossly ignorant about caudates, what are you going to do...They are one of those animal groups that get overlooked.
The effects of temperature on caudate development are rather well researched and it´s something most of us are quite familiar with. It is very interesting to see how lower temps cause them to develop much slowlier and attain maturity later on. It can be pretty striking sometimes like for example in some high altitude populations of Notophthalmus viridescens which can take up to 7 years to reach maturity.
 

Nowicki418

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I am currently working on the specifics to putting together a brumation experiment. Unfortunatly caudates are not out this time of year and are difficult to find for sale as larvae. It looks like it will be frog tadpoles instead, but thats ok. While I was doing LOTS AND LOTS of research on neoteny I learned a lot about it. Maybe I can still do something with it when I'm working on a Masters in 8 years or so. :D
 

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I came into this thread rather late, but...

If you are looking for more reliable information on any of the topics previously mentioned, look for the following book:
Environmental physiology of the amphibians
By Martin E. Feder, Warren W. Burggren.

Google books lets you see a good bit of the book online, including what looked like all of Chapter 10, "Estivation and Hibernation," which you'll want to read if you are going to pursue an overwintering experiment (brumation is included in that category of behaviors).

Environmental physiology of the ... - Google Books

Just brainstorming here:
An interesting question in this area is whether larvae that overwinter and larvae that hatch during the spring metamorphose at the same time/size? I haven't looked in to this, but a colleague has remarked that in the species of ranid he and I work with, everyone emerges around the same time (May), regardless of whether or not the larvae overwintered. This is likely due to shared environmental conditions triggering metamorphosis (something that has also been well studied). Consider that time may be an issue if you're trying to finish this before you graduate. Ranids, which are the only tadpoles that I know of that overwinter in the US, can take a while to get the job done. Spring peepers (Pseudacris crucifer) are winter breeders, but I suppose that if there is a cold snap in the fall and eggs were laid, the larvae would technically overwinter. Not sure about that. The other hylids, toads, microhylids that we have in MS are all spring/summer breeders, and they emerge before the winter sets in. As for caudates, I'm more familiar with the reproductive/metamorphic cycles of plethodontids than ambystomatids. Many of our plethodontids in MS require nearly or more than a year to metamorphose, providing that the stream they are in isn't ephemeral. Generally, they also oviposit in the fall/early winter, so the hatchlings typically go through at least 1 winter season. If I were to look in to this type of question, I'd likely use ranid tadpoles.

If you've already considered these questions, then you're on the right track. Keep the questions and updates coming!
 
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Nowicki418

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Funny, I got a book called "Environmental Physiology of Amphibians" from the library. At the time I was concentrating on Neoteny so I was mostly reading the section on development and hormone regulation. I'll have to check it out again. Thanks for the tip.

Yes it has been narrowed down to Ranids, speciffically R. pipiens and R. catesbeiana. As there may not be enough time for tadpoles to transform I am considering sub-adults instead of tadpoles.

I don't have much to say as far as inducing netoeny so this is getting off topic. I started a new one.

http://www.caudata.org/forum/newthread.php?do=newthread&f=1181
 

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Well for your Masters, you might consider changing your specimen to Ambystoma mavortium. I've heard and personally seen friends keeping examples of neotony in them, although I'm entirely unimformed about it in tigrinum.:happy:

I am currently working on the specifics to putting together a brumation experiment. Unfortunatly caudates are not out this time of year and are difficult to find for sale as larvae. It looks like it will be frog tadpoles instead, but thats ok. While I was doing LOTS AND LOTS of research on neoteny I learned a lot about it. Maybe I can still do something with it when I'm working on a Masters in 8 years or so. :D
 

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I have also interest in this field and hope I will soon join its course and might need your help also.
 

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This thread is ancient but I can't help chiming in. You are looking for prolactin, or at least that seems like the obvious choice when it comes to metamorphosis suppressing endocrinological hanky panky. And by all means experiment away - even an amateurish scientific experiment is more ethically defensible than keeping animals in captivity for idle amusement (pets).
 
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