Devo Lect 20 - Amphibian Meta.

Question 2

Metamorphosis definition

Answer 2

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

Question 3

Main control of metamorphosis

Answer 3

Hormones play key role

Question 4

Table 18.1 comparison

Answer 4

yeah

Question 5

Lateral line

Answer 5

Pressure sensors found in fish and in tadpoles

Question 6

Mauthner neurons

Answer 6

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

Question 7

Early Experiments in metamorphosis

Answer 7

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

Question 8

Thyroxine experiments

Answer 8

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

Question 9

Thyroid hormone pathway

Answer 9

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

Question 10

Intestinal remodeling in metamorphosis

Answer 10

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

Question 11

Stromelysin signaling

Answer 11

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

Question 12

Environmental endocrine disruptors and amphibians

Answer 12

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

Question 13

BPA and amphibians

Answer 13

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

Question 14

Atrazine and xenopus

Answer 14

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

Question 15

Neoteny

Answer 15

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

Question 16

Mexican axolotl

Answer 16

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

Question 17

Mud puppy

Answer 17

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

Question 18

Direct Development

Answer 18

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

Question 19

Gastric brooding frogs

Answer 19

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