Phylum Chordata Subphylum vertebrata

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Phylum Chordata Subphylum vertebrata

• Amphibians (Chapter 19)

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Early TetrapodsModern Amphibians
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Land Invasion

• Early invaders of land
• Vascular plants
• Pulmonate snails
• Tracheate arthropods
• Amphibians (or their ancestors) were likely the
  vertebrate invaders

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Challenges of life on land

• Animals are mostly made of water
• Moving to dry land is dangerous
• But the rewards were open niche space
• Air is 1,000 times less dense than water
• Endoskeleton must be evolved to support invasion
  of land

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A step in the right direction.

• Devonian (400 MYA) was unstable
• Floods, droughts
• Ephemeral waters
• Only species that could survive are fish with
  lungs

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Evolution of land dwellers

• Number of blood vessels increased
• Double circulation oxygenated blood flows
  directly into the heart
• Lobe fins slowly changed to adapt for walking

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Eusthenopteron

• Lungs
• Walking fins
• Likely could walk around mud

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Acanthostega

• Digits on all 4 limbs
• Body was still dragged

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Ichthyostega

• Walking muscles increased
• Still inefficient
• Retained fin rays and opercular bones

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Limnoscelis

• Finally 5 digits per foot
• This became the tetrapod standard

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A step in the wrong direction

• Carboniferous (3600 MYA)
• Climate was uniform
• Tetrapods radiated in water
• Swamps
• More adaptations to survive in water
• Slimmer bodies
• Legs weakened
• Webbing on hind legs

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Modern Amphibians

• 6,433 species (Frost et al., 2006) living
  species
• Most are tied to water
• Eggs aquatic
• Larvae depend on gills
• Thin adult skin looses water quickly
• Ectothermy restricts their range

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Amphibian Characters

• Tetrapods
• Three-chambered heart
• Eggs covered by membrane
• Respiration sometimes by gills
• Limbs usually with 4 digits
• 10 pairs of cranial nerves

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Class Amphibia

• O Gymnophiona
• O Caudata
• O Anura

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O Gymnophiona

• 174 species, tropical
• Snake-like
• Elongate
• Limbless
• burrowers
• Diet worms and other invertebrates
• Most are blind

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Parental investment by skin feeding in a
caecilian amphibian
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O Caudata

• 580 species, temperate regions
• Limbs are at 90 degree angle to body
• Some have lost limbs
• aquatic
• Carnivorous
• Ectoderms with low metabolic rate

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Reproduction

• Most are restricted to water due to aquatic
  larvae
• Few are completely terrestrial
• Undergo direct development and hatch as miniature
  adults
• Some newts change habitats
• Larvae aquatic
• Juveniles terrestrial
• Adults aquatic

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Salamander Sex!
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Spermatheca
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Ambystomatidae
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Breeding Mechanisms in Ambystoma

• General description of courtship using A.
  laterale as an example
• Courtship has 5 stages.

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Male Ambystoma laterale
Female Ambystoma laterale
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Stage 1 Awareness and Overtures
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Stage 2 Capture of the Female Phase I
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Stage 2 Capture of the Female Phase II
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Stage 2 Capture of the Female Phase III
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Stage 2 Capture of the Female Phase III
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Stage 3 and 4 Initiation of Spermatophore
Deposition and Spermatophore Deposition
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Stage 5 Insemination of Female
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Plethodontidae
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After Mating Female Lays Eggs
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Respiration

• Highly variable
• Cutaneous respiration vascular nets in skin
• Oxygen
• Carbon dioxide
• Gills and/or lungs
• Some loose gills at metamorphosis
• Some aquatic forms lose gills completely

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Mole Salamanders Family Ambystomatidae have
gills and lungs in the larval stage.
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Lung less Salamanders Family Plethodontidae
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Paedomorphosis

• The phenomenon of attaining reproductive maturity
  while retaining the larval external morphology
• Eliminating ancestral adult morphology is a trend
  in salamander evolution
• Retention of gills
• Metamorphosis
• Larval appendages
• Some can change based on environmental conditions

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The Big Picture

• Land dwelling tetrapods evolved from lobed finned
  fish
• Land was the next logical environment to invade
• Three orders
• Paedomorphosis has been important in salamander
  evolution

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Frogs and Toads
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O AnuraFrogs and Toads

• 5,679 species
• First appeared 150 MYA
• Restricted to aquatic environments
• Larva and adult are very different

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What is this Chorus Frog Doing?
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Life Cycle

• Most frogs are solitary
• Vocal during mating season
• Hibernate on bottom of streams
• Live off stored glycogen and fat
• Frost-Tolerant
• Adding chemicals to body fluids
• Lowers freezing temperature
• Protection by poison gland

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Poison darts of Colombian Indians
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Reproduction
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Reproduction

• After maturing of the eggs, females move into
  water
• Amplexus male grabs the female from behind
• As eggs are discharged, male discharges sperm
  over them
• Development starts immediately

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Frogs in Amplexus
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Frogs in Amplexus
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Tadpoles Larval Stage

• Initially have gills only.
• Later have gills and lungs.

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Tadpoles of 4 Species. Pawnee Lake, Lancaster
County Nebraska. Tadpoles are Herbivores that
feed on alga!
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Bullfrog pollywog
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Intestine of a 4 cm svl bullfrog tadpole is 120
cm long!
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Intestine
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Tadpole Mouth Parts
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Tadpole Mouth Parts
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Tadpole and Adults

• External structure
• Adults loose long finned tails
• Adults gain legs
• Internal anatomy
• Gills replaced by lungs
• Intestine shortens
• Behavior
• Feeding
• Movement
• Habitat

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Tadpole and metamorphosed frog digestive system.
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Adult Frogs are Predators

• Most are Gape Limited Sit and Wait Predators.
• Some are Active Foragers (toads).

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The North American Bullfrog Rana catesbeiana
biggest frog in North America
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Adult North American Bullfrog and Northern
Leopard Frog
M. Bolek
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What is the Biggest Frog in the World?
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Goliath frog, Conraua goliath
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Frogs and Toads of Oklahoma and USA.
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True Frogs Ranidae
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Leopard Frog Complex

• Rana pipiens group
• These are Semi-terrestrial Frogs

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Plains Leopard Frog
Northern Leopard Frog
Southern Leopard Frog
Pickler Frog
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Males have Nuptual Pads to hold the Female during
amplexus
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Rana pipiens Eggs
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Bullfrog group Aquatic Frogs
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Female Green Frog Male
Green Frog
Female Bullfrog
Male Bullfrog
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Green Frog Eggs
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Wood Frog Terrestrial True Frog
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Toads Family Bufonidae
These are Terrestrial Anurans
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True Toad Anatomy
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American Toad
Great Plains Toad
Southern Toad
Oak Toad
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Toad Eggs
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Woodhouses Toad
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Tree Frogs Family Hylidae

• These Frogs are Predominantly arboreal with
  sucker like toe pads.

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Cricket Frog
Spring Peeper and W. Chorus Frog
Green Treefrog
Copes Gray Treefrog
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Spadefoots Family Pelobatidae

• Predominantly fossorial

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Reproductive strategy of anurans
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Eleutherodactylus sp.
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Pipidae The Tongueless Frogs
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Darwins Frog
Rhinoderma darwinii Duméril and Bibron, 1841
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Darwins Frog
Rhinoderma darwinii Duméril and Bibron, 1841
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The Cane Toad

• The cane toad (Bufo marinus) is native to South
  and Central America
• Cane toads can grow up to 24 cm and can weigh up
  to 1.8 kg (4 lbs)
• Introduced into Queensland in 1935
• Toads were introduced to get rid of the cane
  beetles

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A 861-gram male is the biggest caught anywhere in
the Northern Territory, Measuring 20.5cm
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Native to S. America
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World Distribution of Cane Toad
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Good idea gone very bad

• Cane toads turned out to be worthless at
  controlling the cane beetle
• No natural predators in Australia
• Spread over large area
• They are poisonous
• Secrete bufotoxin from the glands behind their
  head
• Dogs and cats that bite these giant toads die
  within a few minutes

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Problems caused by CT

• Poisonous
• Decline in most other amphibians populations
• Eat everything that will fit into their mouths

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What to do with Cane Toads?
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The Big Picture

• Many Anurans go through extreme morphological and
  life style changes through their life cycle
• The introduction of animals for biological
  control can result in environmental disaster