PHYLUM CHORDATACLASS AMPHIBIA

“AMPHIBIOUS” – (1) able to live both on land and in water (2) combining two characteristics

Australiancane toad

Golden Toads in Costa Rica

Last seen: 1989

Oriental Firebellied Toad

Male American toad using his dewlap to produce a mating call

Asian horned toad

Q: Tetrapods did something remarkable … what??

A: They left water and invaded land

Why such a big deal??

- life originated in water- all phyla evolved in water- animals are mostly water- all cellular activities occur in water

Why leave water??

CLASS: List environmental differences between water & land that demanded change

1) Air is less dense … less supportive

New supportive skeletonsNew musculature to move the new bones

2) Land air temps fluctuate widely & quickly

Amphibs have limitations in latitudes and elevations (poikilotherms)

3) Air has much more O2 (20%) … but how to get it??

Needed: respiratory and circulatory change

4) Air is dessicating

Needed: new skin and new kidney

5) Air carries different “information”

Needed: new sensory systems

Lateral lines lost – Ears gained

Gas detection gained (olfaction)

Transition began during the Devonian … 400 mya

DEVONIAN: alternating floods and droughts…

Streams & ponds were subject to poor water quality … and disappearance

Fishes able to move short distances on land to another pond may have been favored

Devonian survivors were fishes with gills AND “lungs”

Suggested similarities in the locomotion of sarcopterygian fishes (a) and salamanders (b)

http://www.youtube.com/watch?v=SvRtOYGMWV8

Eusthenopteron – lobe-fined fish from the late Devonian Period. Note pectoral fin attached to the skull. Acanthostega – early Devonian

tetrapod – Note forelimb bones (nota strong walker)

Ichthyostega – Devonian tetrapod. Note limbs (probably a walker)

Limnoscelis – Carboniferous tetrapod - Note pentadactyl limbs

Unpredictable Devonian led to the stable CARBONIFEROUS

Warm-swampy-mosses-ferns (amphibian friendly)

Large tetrapod radiation in the Carboniferous

CHARACTERISTICS OF AMPHIBIANS

1) Bony endoskeleton – variable number of vertebrae

2) Usually 4 limbs – forelimb usually with 4 digits

3) Smooth skin w/many glands – pigment cells common

4) Mouth large w/teeth on one or both jaws

5) 2 nostrils open into mouth cavity

6) Respiration by some combination of lungs, skin, and gills

7) 3-chambered heart with a double circulation through the heart

8) Predominantly oviparous – mesolecithal eggs w/gelatinous membrane coverings

MammalianSkin

Dead & Dry (keratinized)

MAMMAL

ToadSkin??

AntipredatorAntibiotic

Exocrine Glands

ChromatophoresColor intensifies when cytoplasm “streams” throughout the cell distributing pigment granules

Pigment Diversity: brown, green, red, yellow, blue

Alkaloid – 200X morepowerful than morphineas an analgesic

One of the most toxic knownsubstances - lethal dose forhumans < 200 μg (cardiac arrest)

AmphibianSkin Toxins

Mayoruna Indian

European fire-bellied toad

Hong Kong newtCryptic Coloration

Bright Coloration

Aposematic (warning) Display – showing off colorful, conspicuous skin which reminds experienced predators about toxicity (dorsal skin is camouflaged)

Newton’s Law of Universal Gravitation applied to amphibians on earth

9.8 m/s/s

Why is gravity so “punishing” to terrestrial animals??

Life on LandMusculoskeletal Demands

Pectoral Girdle & Forelimb

Pelvic Girdle &Hindlimb

salamander

Ventral Dorsal

TriassicFossil

Modern Anuran

+ SKIN

Amphibian Respiration

Surface of Gill or Skin or Lung

(Air or Water)

Surface AreasFrog – 20 cm2/cm3

Human – 300 cm2/cm 3

Positive-Pressure Breathing(muscular glottis & naris)

+

gasexchange

BLOOD FLOW??

O2

CO2

Blood Route in Fish

Red – oxygenatedPurple – partially oxygenatedBlue - deoxygenated

NITROGENOUS Waste Products of Animals

Ammonia Urea Uric Acid

Cost of Synthesis none low high

Toxicity high moderate low

Solubility high high very low

Diffusion Coefficient high intermediate low

N per osmotic particle 1 2 4

(bugs)

HydratingEnvironment

Review Nephron

The Freshwater Problem

Frog vs Toad??

Amphibian Nephron(uncoiled)

pre-urineresembles

plasma

Na+ and Cl- are reabsorbedTubule is water permeable

Na+ and Cl- are reabsorbedTubule is water impermeable

DiluteUrine

Class AmphibiaOrder Anura (without tail)

- > 5000 species of frogs & toads- radical metamorphosis- tailed larval stage- jumpers- toads: dryer skin & shorter legs

bullfrogRana catesbeianna

leopard frogRana pipiens

American toadBufo americanus

http://www.youtube.com/watch?v=bjKB4rWayb8&NR=1&feature=fvwp

(stapes)

Low-frequency hearing(< 4000 hz …usually much less)

Rods and Cones (good vision)

Relaxed eye is set for distance … lens moved forward for near vision

HolometabolousInsects?

Class AmphibiaOrder Urodela (w/tail)

-Salamanders (~ 500 species)- 4 legs of ~ equal size- carnivores- internal fertilization- terrestrial species use a direct

development

Northern dusky salamanderDesmognathus fuscus fuscus

Spotted salamanderAmbystoma maculatum

Redback salamanderPlethodon cinereus

Japanese GiantSalamander

Life Cycle of the Red-spotted Newt

29 mm- 7 mm- ? mm

mudpuppy