Bio II

Rupp

Background

Evolved 370 mya from sarcopterygii Name means “double” “life”

Adaptation to Land Bad hypothesis

Movement overland from shrinking pools of water to larger pools

Short overland crossing do not allow time for change

Better hypothesisEscape from predation and competition to

land where resources were plentiful—insects and plants

Characteristics of Early Amphibians

Similar to sarcopterygiiSkullLimbsShape

Icthyostega continued

Four strong limbs—homologous to pectoral fins

Lung breather Teeth for eating fish Seven toes on hind foot—today’s

amphibians have five

Diversification

Evolutionary split in the Devonian and Carboniferous period

One line became modern amphibians

Diversification continued

Other line was forerunner to modern reptiles

Approximately 4500 species of amphibian todayAnura—3000 speciesUrodela—400 speciesApoda—160 species

Modern Characteristics

Aquatic Larva to Terrestrial Adult--Metamorphosis

Moist, thin, scaleless skin

Claw-free feet, typically webbed

Gills, lungs, and skin for respiration

No multicellular egg membranes

Large mouth with upper and lower teeth

Three-chambered heart

Ectothermal

Paired kidneys

Ten pairs of cranial nerves

Separate Sexes

Order Anura Name means “without

tail” Frogs and toads Found worldwide

except polar regions Toads = rough and

bumpy skin Frogs = smooth and

moist skin

Spend at least part of their life in water, some are totally aquatic

Built to jump Long, strong hind legs Short, shock absorbing

forelimbs Eat almost anything Return to water for

fertilization and mating Larval tadpole stage

Toad versus Frog

Order Urodela Tailed amphibians Elongate body, long

tail, moist skin, four limbs

Few centimeters to 1.5 meters long

Carnivorous Typically nocturnal Found in the

Americas, Africa, Asia, and Europe

Many lay eggs in water—metamorphosis

Family Plethodontidae is the largest group—lungless, gas exchange through skin

Terrestrials hatch into mini adults—direct development

Internal fertilization—spermatophore

Some females retain eggs until hatching

Necturus

Urodelans

Urodelans

Urodelans continued

Paedomorphosis—retention of pre-adult structures

Non-metamorphic species are termed perennibranchiate

Apodans Name means “without

feet” Typically called

caecilians Resemble snakes Average 30cm in

length some reach 1.5m

Small eyes located under skin or bone—typically blind

Burrowers

Relatively little is known

Teeth for prey capture Chemosensory

tentacles on head Believed to have

internal fertilization Some females stay

with eggs until hatching

Some are viviparous Found in Asia, Africa,

and S. American tropical regions

Apodans continued

External Covering

Two major functionsRespirationProtection

Gas exchange is aided by mucous glands to keep the skin moist

External covering continued

May secrete poisons May desiccate

quickly if not near water

Nocturnal to avoid desiccation

Internal Anatomy

Strong vertebral column to support weight on land

Strong limbs Pectoral and pelvic

girdles Cervical vertebrae

for neck movement

Internal Anatomy—circulatory system Double circulation—two loops Pulmonary circulation—carries

deoxygenated blood from heart to lungs Systemic circulation—carries

oxygenated blood to body Faster blood flow than a single loop

system like fish

Internal Anatomy—circulatory system continued

Internal Anatomy—circulatory system continued

First division in pulmonary and systemic pumping

Deoxygenated blood enters sinus venosus of right atria

Oxygenated blood enters left atria

Blood enters the ventricle—structure minimizes mixing of bloods

Conus arteriosus valve separates blood and sends to lungs or body

Respiration Larval amphibians

use skin and gills Adults use skin and

lungs Cutaneous

respiration is important due to small surface area of lungs

Positive pressure breathingThe mouth changes

the pressure in the airway

Nostrils control direction of the airflow

Respiration continued

Digestive system Adults are

carnivorous Larvae are typically

herbivorous

OrgansPharynxEsophagusStomachLiverGall bladderSmall intestineLarge intestineCloaca

Digestive system continued Elastic stomach and

esophagus allow swallowing of large prey

Stomach secretes gastric juices

Pyloric sphincter allows digested food to move to the small intestine

Upper portion of small intestine is the duodenum

Middle portion of the small intestine is the ileum

Digestive system continued Mesentery holds the

small intestine together

Digested food, urinary wastes, and eggs and sperm pass into the cloaca before exiting the vent

Liver produces bile stored in the gall bladder

Pancreas secretes enzymes to help break down food in the small intestine

Excretory system Kidneys are the

primary organ One located on each

side of the spine Filter nitrogenous

wastes, mix with water, and excrete as urine

Kidneys to urinary ducts to urinary bladder

Bladder can serve as a water reservoir organ in dry times

Larval amphibians excrete ammonia which is toxic

Adults transform ammonia into urea, which is less toxic and conserves water

Excretory system continued

Nervous system Brain is divided into lobes

OlfactoryCerebrum—behavior and learningOptic lobesCerebellum—muscular coordination, not well

developedMedulla oblongata—involuntary muscle control,

heart and breathing Ten pairs of cranial nerves Spinal cord and PNS

Sense organs

Larval amphibians have a lateral line system like a fish—it is lost during metamorphosis

Sense organs continued

EyesCovered by nictitating

membraneLarge optic lobes

Sense organs continued Hearing

Tympanic membrane—external eardrumColumella—small bone between typanum and

internal earInner ear fluid carries vibrations from columellaSounds are converted to electrical impulses by

small hair cellsElectrical impulses are transmitted to the brain

Reproduction—life cycle Males have bean-shaped testes near the

kidneys During breeding the sperm cells pass to

kidneys, then urinary ducts, then the cloaca Females have thin-walled ovaries located

near the kidneys Eggs mature, burst through the ovaries,

move towards oviducts, become coated in jelly-like material, and exit the cloaca

Reproduction—courtship and fertilization Mating calls are species unique—caused

by forcing air back and forth from lungs to mouth over vocal sacs

Amplexus—males climb onto female and embrace her

When the female releases the eggs the male coats them in sperm—direct external fertilization

Frog calls

Reproduction-courtship and fertilization

Reproduction--metamorphosis A few days after

fertilization tadpoles hatch

Tadpoles survive using an attached yolk sac

Develop three pairs of gills Development of

operculum Spiracle on left side

Mouth eventually opens, legs grow, and tail and gills disappear

Thyroxine is the hormone responsible for causing the physical changes

Reproduction—metamorphosis continued

Reproduction—metamorphosis continued Some species do not lay eggs in water, but

they find a moist place or construct small nests

Some salamanders remain in a larval stage their entire lives (Mexican axolotl—paedomorphosis) (Necturus—perrenibranchiate)

Some amphibians bypass metamorphosis and hatch as miniature adults (metamorphosis in egg) (Longtail salamander)

Reproduction—metamorphosis continued

Reproduction—parental care

Some species offer protection to their young

Many times the father is the protector

Male Darwin frog, Rhinoderma darwinii, takes young into his vocal sacs—they hatch and go through metamorphosis in his body (found in Chile)

Reproduction—parental care continued

Female gastric-brooding frogs (probably extinct) Swallow the eggs Development in stomach Stomach stops producing

acids during brooding

Some females sit on their eggs, typically poison dart frogs

Reproduction—other parental care strategies

Reproduction—other parental care strategies