Devo Lect 20 - Amphibian Meta. Flashcards Preview

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Flashcards in Devo Lect 20 - Amphibian Meta. Deck (18):
2

Metamorphosis definition

Reprogramming of the body, changing from young body to adult body. Requires changes in gene expression. Examples: lose tail, gonad matures, etc

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Main control of metamorphosis

Hormones play key role

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Table 18.1 comparison

yeah

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Lateral line

Pressure sensors found in fish and in tadpoles

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Mauthner neurons

neurons in fish and tadpoles responsible for reflex to get away from predators

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Early Experiments in metamorphosis

powdered horse thyroid glands: induced early metamorphosis; remove thyroid gland: no metamorphosis, giant tadpoles!

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Thyroxine experiments

Cut off tail, add thyroxine: induced lots of cell death. Add to a live tadpole: much faster metamorphosis

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Thyroid hormone pathway

T4 (thyroxine) and T3 (active); bind to receptor (TRa or ß) then transported into nucleus to bind

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Intestinal remodeling in metamorphosis

Stromelysin: degrades ECM; turned on by TH in the intestine; makes more space (in situ). Apoptosis: lots of cells die (TUNEL)

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Stromelysin signaling

Turned on by TH; acts as an initiator of apoptosis; if you inhibit stromelysin you get lots less apoptosis

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Environmental endocrine disruptors and amphibians

Used as test subjects because they absorb through skin. Estrogen, DDT, dioxins (industrial), Atrazine (herbicide), Bisphenol A

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BPA and amphibians

Low [BPA]: no big effect; BPA and TH: inhibits the effect of TH! blocks metamorphosis

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Atrazine and xenopus

Atrazine promote aromatase, causes testosterone to become estradiol; results in feminization of males: find oocytes in testes, feminine behaviour, can’t produce sperm properly - pseudofemales

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Neoteny

Animal which fails to undergo metamorphosis and attains sexual maturity in its “larval” form (eg mexican axolotl)

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Mexican axolotl

Doesn’t complete metamorphosis (neoteny) because it have no active TSH (pituitary defect); Retains external gills. If you add TH, they become more salamander like - undergo metamorphosis

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Mud puppy

Necturus; Salamander that does neoteny; no receptor (TRß). Cannot be tricked into metamorphosis

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Direct Development

Amphibians that don’t go through a larval stage; eg Puerto Rico little frog; develops legs in the egg; not a lot of water there, so it probably evolved to avoid that

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Gastric brooding frogs

Normal development, except that females swallow the fertilized eggs and they develop in the stomach, then are vomited out when froglet; turn off digestive system; extinct