h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Aztec words have a really great ring to them.

The lack of metamorphosis is really strange. It's apparently caused by the amount of iodine in the water; the volcanic lakes where they live don't have much iodine, but in other parts of Mexico iodine is readily available. In the iodine-deficient water they can't produce the hormone thyroxine (also called T4: it has 4 iodine atoms per molecule) so can't induce metamorphosis. This is fine because they're quite happy just splashing about without lungs. With iodine they can develope lungs and live on land but must breed in water.

Why these features are linked (iodine and lungs) I don't know, presumably there's a reason. Any suggestions?

I have no idea... the only organ I've heard iodine connected to is the thyroid gland, and I don't know if axolotls even have them.

I have also heard, though its truth is disputable, that drought conditions can also cause an axolotl to "grow up". That is, being confined to a small pool of shallow muddy water, basically. Maybe this is also related to the iodine, somehow.

Good idea. Perhaps the concentration of iodine rises as the pool dries, prompting metamorphosis so the axolotl has a means of escape to a deeper pool. Thanks for that - might help in exams.