bio ii rupp. background evolved 370 mya from sarcopterygii name means “double” “life”
TRANSCRIPT
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