Why do caterpillars metamorphose?

[motorollin]

I can understand that caterpillars might have an evolutionary pressure to grow wings in order to evade predators or find food and mates. But normally when survival of the fittest is in play, the unfit members (in this case those without wings) will not survive or find food/mates. Either way, their genes will not be progressed. I would expect this to lead either to an extinction of the caterpillar species in favour of the butterfly/moth species, or a separation of the two in to separate species. So what is the advantage of the eggs hatching as caterpillars and then changing in to butterflies/moths? Why would this a metamorphic behaviour be evolved rather than an evolution to a different species?

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moto

[A4000_Mad]

Why do caterpillars metamorphose?

They get jealous when they see birds up in the sky :-D

But it is incredible how a skin full of pus can turn into legs and wings and start flying  8-)

 :popcorn:


A4000 Mad

[motorollin]

A4000_Mad wrote:
They get jealous when they see birds up in the sky :-D

:roll:

A4000_Mad wrote:
But it is incredible how a skin full of pus can turn into legs and wings and start flying  8-)

Well done, you just managed to make something beautiful and incredible sound totally revolting :lol:

A4000_Mad wrote:
 :popcorn:

Indeed. I am observing a Vapourer Moth which I am keeping in a glass with a breatheable cover and a load of leaves :-) It is starting to coccoon itself now. I'm thinking of setting up a webcam to take pictures every 10 seconds so I can make a high speed animation of the process.

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moto

[JaXanim]

motorollin wrote:
- - - - - - - - - I would expect this to lead either to an extinction of the caterpillar species in favour of the butterfly/moth species, - - - - - - - -

But that's not what evolution did. Your process says that at one time only caterpillars existed. Then, through evolutionary pressures some caterpillars evolved or branched out into a separate species (butterflies say). Evolution would require the existance at some point, of caterpillars and butterflies as two different animals, together with some 'intermediate' forms (stubby-winged caterpillars say), analogus to the 'missing link'. Each separate species would live and die separately with no interconnection between them. That's not what happened. Metamorphosis is a  mechanism used by thousands of species to develop from the infantile form into an adult. It's their life cycle. Of course evolution generated all these mechanisms. Where it got involved in your scenario was in the generation of lepidoptera from segmented worms, which in turn came from from molluscs. Next was the differentiation of caterpillars into moth and butterfly larva as separate families of insects.
Cheers, JaX

[mel_zoom]

If you think about it the metamorphosis from catepillar to butterfly or moth is just one particularly striking example of a process that occurs in very many living things.

I dont believe there was ever just a caterpillar species that evolved wings in order to overcome an environmental stress. As you say there would be a total divergence. Instead the caterpillar is just the infant larval form of the adult species. The vast majority if not all insects have a similar larval stage - the eggs are too small to allow for the growth of a fully fledged insect in the same way as many higher order egg-laying creatures.

[motorollin]

Ok I understand what happened, but why did they not evolve in to a different species? I still don't understand the evolutionary advantage of larvae which develop in to the mature adult rather than just being born as the butterfly in the first place.

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moto

[motorollin]

mel_zoom wrote:
The vast majority if not all insects have a similar larval stage - the eggs are too small to allow for the growth of a fully fledged insect in the same way as many higher order egg-laying creatures.

I think this is the answer to my question :-)

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moto

[bloodline]

Bear in mind that the evolution of the Catapillar and the butterfly are independant.

Natural selection of one does not affect the other. This process allows the same set of genes to function in different environments. As Mel satates all insects have a descrete larval stage so clearly at some point their common ancestor developed this trait, and since it allows better use of of the resources. It was clearly an advantage and has persisted, some highly social insects undergo their laval stage while still in the egg. This makes sense since if you think about it.

(pick up a few Richard Dawkins books on natural selection and that should give you a clear idea of what's happening)

What is weird to think though, is that inside the catapillar are a few cells that do nothing, but have been their since it hatched from it's egg... then when the catapilla enters its cacoon, these cells then secrete enzymes that digest the rest of the catapillar... and the butterfly grows from these cells which feed off the catapillar... weird huh!

[motorollin]

bloodline wrote:
What is weird to think though, is that inside the catapillar are a few cells that do nothing, but have been their since it hatched from it's egg... then when the catapilla enters its cacoon, these cells then secrete enzymes that digest the rest of the catapillar... and the butterfly grows from these cells which feed off the catapillar... weird huh!

Revolting :lol: Does the caterpillar die then?

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moto

[bloodline]

motorollin wrote:

bloodline wrote:
What is weird to think though, is that inside the catapillar are a few cells that do nothing, but have been their since it hatched from it's egg... then when the catapilla enters its cacoon, these cells then secrete enzymes that digest the rest of the catapillar... and the butterfly grows from these cells which feed off the catapillar... weird huh!

Revolting :lol: Does the caterpillar die then?

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moto

well the butterfly cells are genetically identical to the Catapillar ones, and have always been part of the catapillar... so technically no...

[motorollin]

I wonder why they evolved a larval phase rather than just laying bigger eggs with tiny, fully-formed butterflies inside?

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moto

[mel_zoom]

motorollin:
"I wonder why they evolved a larval phase rather than just laying bigger eggs with tiny, fully-formed butterflies inside"

Well the eggs are always going to be considerably smaller than the adult organism which implies the embryonic form would be smaller still. Producing a large enough egg would limit the number that can be produced due to the biological resources needed to produce them.

Even if they could lay a larger egg its also very unlikely that the resultant tiny infant insect would have a high probability of survival anyway. This is because it is unlikely that the principal benefit of their adult form - that is the ability to fly - is going to be effective when they would be perhaps a millimetre in size.

So you get a lot of effort in producing something with poor survival chances. Producing larger numbers of what amount to plant eating machines that can grow to a considerable size very quickly and then use the stored chemical energy to transform into the adult seems a better strategy for survival. Its obviously a strategy that works since all insects seem to use it. I cant think of any examples that follow your reptile-like pattern of producing perfectly formed minature offspring.

[bloodline]

motorollin wrote:
I wonder why they evolved a larval phase rather than just laying bigger eggs with tiny, fully-formed butterflies inside?

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moto

Note that the larval stage often (though there are exceptions, see dragon flys etc...) lacks an exoskeleton, thus allowing the organisim to grow from a convenient birth size (i.e. the adult needs to lay 10's of eggs, thus they have to be much smaller than the adult) to a convenient adult size. Adults often do have an exoskeleton which is prety much set in size and unless the organism is able to molt (not something insects do, unlike spiders and woodlice etc...) then the adult is of a fixed size (the largest size the larva got to before metamorphosis).

[motorollin]

My Vapourer moth has emerged :banana: It's wingless so is a female. She has laid some eggs on one of the leaves. Is it usual for moths/butterflies/insects to lay eggs whether they are fertilised or not?

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moto

[motorollin]

Well regardless of why it happened, here is what emerged from the cocoon created by the caterpillar I caught. I have released her in to the garden now, so she is free to lay useless unfertilised eggs, and lie helplessly as predators consume her wingless body. Ahhh, the beauty of nature.

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moto