Embryology Biology 441 Spring 2014 Albert HarrisMetamorphosis
MetamorphosisTadpole ----> Frogs & toads1* Self-destruction of tail - Apoptosis
Illustration of tail onto which the eye was grafted [Textbook Fig 16.6, page 555 (Schwind)]
2* Formation of legs
3* Change in retina: different light-detecting pigment
4* Movement of eyeballs to more anterior location 5* Formation of lungs 7* Degeneration of gills 8* Changed hemoglobin; different cells blood-producing stem cells for breathing air 9* Kidney changes - adult uses urea instead of ammonia 10* loss of lateral line system 11* Digestive tract herbivorous--> carnivorous (shorter in length) 12* Skin thicker epidermis and dermis -------------------------------------------------------------------------------------- Important that these changes occur in the right sequence: "Don't destroy your tail until you have formed your new legs"
Threshold theory Gilbert regards as an over-simplification --------------------------------------------------------------------------------------
Stimulation of amphibian metamorphosis by thyroxine : The thyroid gland evolved from a mucus-secreting groove, which then became separated from the floor of the throat Thyroxine is made from mucus inside epithelial spheres; covalent binding of iodine to tyrosines + binding of pairs of tyrosine. This polymerization occurs in the mucus inside the epithelial spheres. ? related to evolution of thyroid from the mucus-secreting gland used for filter-feeding by sea squirts and larval lampreys -------------------------------------------------------------------------------------- Salamanders also have larvae, with legs, that undergo metamorphosis, in a sub-group of salamanders called newts (common in this area: more in New England; very poisonous skin) Larva -> Eft --> Newt -------------------------------------------------------------------------------------- Neoteny - Axolotl Reach sexual maturity and breed when anatomically still larvae. -------------------------------------------------------------------------------------- Also there are species of frogs and salamanders with "direct development" -------------------------------------------------------------------------------------- Invertebrate examples of metamorphosis II) Ammocoetes larva ---> Lamprey III) Sea Squirt "tadpole" ----> Sea Squirt IV) Pluteus ----> Sea urchin (and star-fish, etc.) V) Sponges have a swimming larval form, whose cells then rearrange to form a sponge (in which cells keep on rearranging forever) VI) Trochophore larvae, Pilidium larva, and several other planktonic larvae VII) Larvae of barnacles look like shrimp, etc. -------------------------------------------------------------------------------------- VIII) Caterpillar ----> ----> ----> Butterfly, or moth Maggot ----> ----> ----> fly grasshopper -> grasshopper -> grasshopper -> grasshopper -> grasshopper silverfish -> silverfish -> silverfish-> -> silverfish -> silverfish
Metamorphosis by molting (shedding outer layer of skin) All arthropods molt. Some insects have a metamorphic molt. The new body surface is made by differentiation of imaginal discs. Hormonal control of arthropod molting
Juvenile hormone (a lipid) inhibits metamorphosis
Precor - chemical name methoprene - analog of juvenile hormone Eliminates fleas by preventing them from going through metamorphosis to become breeding adults *****************************************
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