F - Metamorphosis 09

F - Metamorphosis 09 - Metamorphosis: Some generalizations...

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Metamorphosis: Some generalizations § Often accompanies a change in habitat and/or feeding behavior § Hormonal Controls: Thyroid hormones – primary controllers Corticosteroids – generally synergize with and enhance the effects of TH (more well documented in amphibians) Prolactin – acts as a metamorphic inhibitor (better studied in amphibians) Leptin – appears to act as a limb growth signal in amphibians (not yet studied in fish).
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Metamorphosis: Some generalizations § Adult structures must develop/grow at the same time as larval structures are destroyed via apoptosis This requires a tremendous level of coordination at the cellular and whole organism levels § Regulation of the TH, corticosteroid, and PRL axes may occur at all the levels we’ve previously discussed
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Metamorphosis: Developmental Stages § Premetamorphic – Larval stages (early tadpoles) No TH influence yet Limited developmental changes do occur § Prometamorphosis TH are on the rise Noticeable growth & development of external and internal organs § Metamorphic Climax TH levels peak Rapid reorganization (differentiation) of existing organs, and development of new adult organs Rapid resorption of the larval organs (e.g. tail)
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Metamorphosis: Anurans (tadpole to frog) § Tremendous flexibility in timing of metamorphosis § Environmental influences on metamorphosis? Temperature water availability Crowding Daylight hours Diet and food availability Environmental iodine levels § How/why do these factors affect anuran development?
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Metamorphosis: Anurans (tadpole to frog) § Anuran metamorphosis includes changes in: Behavioral changes – switch feeding modes Habitat and ecological changes – many go from aquatic to terrestrial habitats External and Internal anatomy & adult organs are created before larval organs are destroyed
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Thyroid hormones control metamorphosis § Figure 1 from Brown and Cai
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Hind limb development in X. laevis tadpoles Brown D. D. et.al. PNAS 2005;102:12455-12458
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F - Metamorphosis 09 - Metamorphosis: Some generalizations...

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