Question

Metamorphosis in 3 different species and why?
Metamorphosis should include developmental cycle
Phases of the middle stages - transition points
Hormones - major signaling molecules responsible
1 insects species
2 protochordata / eurochordata -- tunicates and amphibians

3 amphibian

Answer 1

Answer

1. Metamorphosis is defined as the change in form i.e nothing but transformation from immature larval form to the mature adult form which involve one or more than one larval stages.
2. in animal kingdom few phyla shows this interesting phenomenon, it is mainly observed in Arthropods , protochordates and amphibians.
3. The main reason behind the metamorphosis is both juvenile and adult occupy different niches and hence there is no competition for the food and place. Even if we observe both this form they also differ in their size, habitat. They can also prevent themselves from being predated because they are in different niches & habitat hence there resources are distributed. These are some of the advantages of metamorphosis.
4. In insects there are 3 types of metamorphosis is observed a) ametabolous b) hemimetabolous c) holometabolous
5. in case of insects two hormones are found 1) Juvenile hormone- which keeps juvenility of animal 2) Ecdysone hormone- which develop from juvenile to adult 3) PTTH i.e. prothoracicotrophic hormone which stimulate corpora allata to produce Juvenile hormone
6. In case of urochordate we have a very good example i.e herdmania in which retrogressive metamorphosis is observed. Here the larva possesses a characters like chordate but eventually when it gets adult the notochord is only persist in the tail hence such type of metamorphosis is called retrogressive type. The reason behind this is larva require additional or advanced feature for the swimming but adult not. Hormonal mechanism in Urochordates is unknown
7. Amphibian include salamander, frog and caecilians like animals. Amphibians require Thyroid hormone for the development from tadpole to adult conversion. Scientist showed that if water not contain enough iodine then the development of amphibians is ceased. There are two forms of thyroid hormone 1) T4 ( Thyroxine) and 2) T3    ( Triiodothyronine) among this two T3 is most important