By what process does a caterpillar change into a butterfly?
Simplified overview: 1) The caterpillar and the butterfly are for the most part made of different cells. In the embryo, certain cells are set aside that will develop into adult structures, whilst the rest of the cells go on to make the caterpillar. The cells that were set aside form structures called “imaginal discs” (“imago” being a term for the adult stage), and they undergo their own developmental program inside the caterpillar. Inside the chrysalis, these imaginal disc cells replace the caterpillar cells. 2) Positional information is provided to cells in the embryo, and informs subsequent development. When the mother butterfly lays her eggs, they already have in them proteins that are positioned in particular places to define which end is the head and which is the tail, and which is the dorsal (back) side and which is the ventral (belly). This system of axes allows each imaginal disc to “know” where it is in the animal, and this information influences the development of the cells i
Thanks to Toekneesan for pointing to my site! There are some better photos of the intermediate stage, HERE about 3/4 down the page. I know that a lot of the caterpillar’s body dissolves and re-forms, but it’s certainly not “just goo” inside. By the time it slipped off its caterpillar skin, this pupa already had distinct buds that would become wings, legs, abdominal segments, etc. I was quite surprised to see that the wings and legs were separate at this point, and then stuck down to the pupa afterward; I had always thought they were inside a solid shell that didn’t alter. It’s my understanding from my reading, that many of the parts stay the same – eyes are still eyes, legs are still legs (although the caterpillar prolegs go away) and many of the muscles remain muscles. Of course, these are MOTH images, not butterfly – but I’m betting that the process is very similar, just with a chrysalis instead of a cocooned pupa.
It is actually not clear. So far, it looked like as you said, there is a complete break down of the cells during the Metamorphosis and any part of the Butterflies Remember What They Learned as caterpillar could become any part of the butterfly. But, it may not be the case because recent research shows that butterflies remember what they learned as caterpillars. This would mean that at least some cells that are part of the neural system are in fact not broken down and keep their functions during the metamorphosis phase.
Some links to get you started on further reading: Imaginal disc on wikipedia. Homeotic genes help to specify what part of the butterfly each imaginal disc forms.
