Metamorphosis

faculty.biol.ttu.edu

Metamorphosis

Metamorphosis


Amphibian

Metamorphosis


Body swim-posture changes

during flounder metamorphosis

as one eye migrates to the

opposite side of the head.

©2006 by The Company of Biologists Ltd

Schreiber A M J Exp Biol 2006;209:610-621


Metamorphosis

1. Change in form of non-reproductive

structures between embryo and sexual

maturity.

2. Different ecological niche for larvae.

3. Morphological changes at the end of larval

life depend upon some environmental cue,

either internal (hormone) or external

(temperature, photoperiod).


Amphibian Metamorphosis

• Anurans (frogs, toads)

– Most undergo metamorphosis with larval and adult

stages

– Some undergo direct development (no free living

larval stage)

• Urodeles (salamanders, newts)

– -most undergo metamorphosis, more subtle

– Neoteny- retention of larval features in breeding adult

• Caecilians- poorly studied with respect to

metamorphosis


Xenopus

laevis,

African

clawed frog

Photo Credit: David Bay, University of Michigan)


Very precise

changes in

anatomy allow

scientists to

stage

metamorphosis

in anurans.

Takes @ 45-90

days


Can take up to

three years in

bullfrogs!


http://aknhp.uaa.alaska.edu/herps/amph_life.htm


Urodele metamorphosis is much more subtle- legs already

formed in larvae


Direct Development

• No larval stage

• Embryos develop directly as small frogs


Direct Development

Eleutherodactylus coqui

http://locallytoned.wordpress.com/2009/08/27/elinsons-coqui-tones/


Factors affecting metamorphosis

• Environmental

– Temperature

– Photoperiod

– Food availability

– Density

– Dessication

http://www.whistlernaturalists.ca/?page_id=95


Wilbur and Collins, 1973


Wilbur and Collins, 1973

• “In our model the ranges of body sizes and

dates of metamorphosis are determined by a

minimum body size that must be obtained

and a maximum body size that will not be

exceeded at metamorphosis. Between these

two size thresholds the endocrinological

initiation of metamorphosis is expected to be

related to the recent growth history of the

individual larva”.


Richter et al., 2009


Density effects may be related to food

intake

• According to the Wilbur Collins model,

tadpoles must reach a minimum body size in

order to metamorphose

• In most experiments, density and resource

availability are necessarily linked

• Richter et al show that if food is not restricted

then density accelerates metamorphosis


Denver, 1998

http://www.flickr.com/photos/8334337@N03/3206893723/in/phot

ostream/

Copyright © 2005 Jack G


Cannibalistic

tadpole

morphology

Crossland et al., 2011, Cannibalistic cane

toad tadpoles

http://www.nwf.org/News-and-Magazines/National-

Wildlife/Animals/Archives/2006/Eating-Among-Friends.aspx


http://news.nationalgeographic.com/news/2009/06/090629-salamanders-hybrid.html


Image by David Pfennig and James Collins.


Factors affecting metamorphosis

• Hormonal

– Thyroid

– Glucocorticoids

– Prolactin

http://www.whistlernaturalists.ca/?page_id=95


I -

I -

I -

I -

lysosomes

TG uptake

I -

I -

TG iodination

TG

TG-R ?

ClO 4- :

•inhibits I - uptake

•blocks T 4 , T 3 synthesis

•causes enlarged thyroid

Na +

Na +

I -

I -

Na +

K +

T 4 , T 3

Blood

Na +

Na +

I -

I -

TSH-R

ClO 4

-


From Shi, 2000


Factors affecting metamorphosis

• Hormonal

– Thyroid

– Glucocorticoids

– Prolactin

http://www.whistlernaturalists.ca/?page_id=95


Neoteny

• Retention of larval characteristics in breeding

adult

• Not observed in anuran amphibians, only

urodeles


Axolotl

Ambystoma mexicanum

Facultative neoteny, can be induced to metamorphose with T3 or T4


Common mudpuppy

Necturus maculosus

Obligate neotene, cannot be induced with T4 or T3


Martinez GM, Bolker JA (2003) Embryonic and Larval Staging of Summer Flounder (Paralichthys dentatus) J Morph 255:162-176.


Okada N, Tanaka M, Tagawa M (2003)

Bone development during metamorphosis of

the Japanese flounder (Paralichthys

olivaceus): differential responses to thyroid

hormone. Proceedings of the 26th Annual

Larval Fish Conference, Browman HI,

Skiftesvik AB, eds. Published by the Institute

of Marine Research, Postboks 1870

Nordnes, N-5817, Bergen, Norway.


Galay-Burgos et al., 2008

Atlantic halibut (Hippoglossus hippoglossus)


A summary of changes in larval swimming and settling behaviors during spontaneous

development, and after metamorphic induction with thyroid hormone (100 nmol l-1T3) or

inhibition with methimazol (0.1 mol l-1) treatment.

Schreiber A M J Exp Biol 2006;209:610-621

©2006 by The Company of Biologists Ltd

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