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Old 28th October 2008   #103
Erin
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Default Re: Metamorphed Axy...

Quote:
Originally Posted by Tim S View Post
Has anyone considered that some of the metomorphing Axolotls that have been reported may be mutations. Neoteny in Ambystoma mexicanum is controlled by a single recessive gene. So, a single mutation back to the ancestral gene (for metamorphosis) will cause the Axolotl to metamorphose.


I believe it's more complicated than that. I actually worked (as an undergraduate) in the lab where most of this research was done. Without re-reading all of the literature and as far as I can remember, when they originally did the experiment, they crossed lab stock A. mexicanum with A. tigrinum. The ratios of paedomorphic individuals among the offspring of such crosses indicated that a single gene might be involved. Here's a ref for the paper if you want to look it up:

Voss, S.R. & H.B. Shaffer. 1997. Adaptive evolution via a major gene effect: Paedomorphosis in the Mexican axolotl. Proceedings of the National Academy of Sciences of the United States, 94(25): 14185-14189.

However, when they later did crosses using wild caught A. mexicanum and A. tigrinum, the offspring ratios indicated that more than one gene was controlling metamorphosis. I think that's all detailed here:

Voss, S.R. & J.J. Smith. 2005. Evolution of salamander life cycles: A major-effect quantitative trait locus contributes to discrete and continuous variation for metamorphic timing. Genetics, 170(1): 275-281.

Anyway, they explained the discrepancy as probably being the result of strong selection against paedomorphic individuals in laboratory strains. Animals that undergo spontaneous metamorphosis are generally destroyed and certainly arenít being used as breeding stock for the available lines. In natural populations, itís a more complicated story, but in the lab strain axolotl it could be a single gene mutation that leads to metamorphosis. However, I think it's much more likely that environmental factors are the cause of most of these cases.

If anyone canít access the papers, just send me a pm and Iíll try to get you a PDF
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