Naked Science Forum
Life Sciences => Plant Sciences, Zoology & Evolution => Topic started by: Kryptid on 10/12/2006 10:21:10
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I've been taking an entomology course this semester. We discussed the hormonal balances required to initiate certain stages of metamorphosis in caterpillars. Here's the sum up as I understand it:
A caterpillar has high levels of juvenile hormone (JH) which prevents it from becoming an adult, and the presence of the hormone ecdysone causes it to molt. The pupa stage has low levels of JH and high levels of ecdysone. Finally, the emerging butterfly has low levels of both JH and ecdysone. According to my learning, a caterpillar can be induced to undergo premature metamorphosis into a tiny adult by manipulating these hormones. So we know that hormonal manipulation has an effect on metamorphosis.
My question: If we manipulate the hormone levels in the adult stage (the butterfly) so that its body now has high levels of JH and ecdysone (the same as a caterpillar's), will the butterfly molt back into its caterpillar stage? How about the pupal stage?
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Hi,
I see your question hasn't been answered yet, so I'll add one thought and bring it back up to the top and maybe someone who knows insects can give you a good answer.
My understanding is that most developmental switches in animals are a one-way trip. For example increasing amount of ecdysone may cause a gene to be transcribed, the RNA translated into a protein, and that protein performs a function which causes the cell to differentiate and become a specialist cell (say an adult eye cell). In most cases this is a one-way process, once you're an eye cell, you normally don't become a liver cell (thank goodness). However, if you add ecdysone to some adult insects you can get them to go through an additional adult molt- but not back to a larvae.
This is one reason for the interest in stem cells. These cells retain their ability to differentiate into different cell types when given the correct stimulus.
Of course if you are thinking of stem cells you should think of plants and fungi- almost all plant cells are "totipotent" so if you take almost any cell from a plant, and give it the correct combination of hormones you can generate a new plant. So far, no one has figured out how to do this with just any animal cell.
Colleen
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Hi,
If you simulate the presence of high JH in immature insects, they stay immature. So for example a 3rd instar larva treated with JH (or a JH analogue), will remain as a larva and even go through supernumary moults to become a giant larva, which eventually is unsustainable and the insect dies. This is the basis of a number of "novel" insecticides such as methoprene. It works fine on insects where the larva is not a pest, (eg mosquitoes) but clearly if you want to control caterpillars eating your cabbages, then giant larva are not desirable. If you treat larval insects with an anti-JH such as precocene, you can induce an immature larva to moult to a tiny non viable pupa. As with most biological processes however, you cannot reverse the developmental process, (ie you can't "persuade" a pupa to revert to a larva). Paradoxically the application of exogenous ecdysone or analogues does not have such dramatic effects on metamorphosis as far as I'm aware.