Amphibians!

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Amphibians!

• Review the general taxonomy and biology of
  amphibians, as well as global patterns of
  distribution and diversity.
• Discuss important groups of amphibians in North
  American freshwater systems life cycles,
  reproduction, habitat requirements, and patterns
  of diversity.
• For the amphibians, you are responsible for
  knowing the information on both the ORDERS and
  FAMILIES we discuss in lecture.

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Amphibians?

• These foul and loathsome animals are abhorrent
  because of their cold body, pale color,
  cartilaginous skeleton, filthy skin, fierce
  aspect, calculating eye, offensive smell, harsh
  voice, squalid habitation, and terrible venom
  and so their Creator has not exerted his powers
  to make many of them.
• - Linnaeus, 1758

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Amphibian Taxonomy

• Kingdom Animalia
• Phylum Chordata
• Class Amphibia

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Amphibian Evolution

• Of the living vertebrates, amphibians were the
  first to adapt to extended periods of time on
  land.
• Most still need fresh water at some point in life
  cycle.
• These multiple habitat requirements are reflected
  in the complex life cycle of most (but not all)
  species.

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The Complex Life Cycle
Costs and Benefits?
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Major Challenges of Life on Land

• Support and locomotion
• Respiration

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Support and Locomotion

• Vertebrae form a suspension girder, with weight
  hung beneath the vertebral column
• Weight transferred through pelvic and pectoral
  girdles to limbs
• Inefficient splay-legged instead of legs
  rotated beneath body

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Respiration

• Lungs, but no efficient way of filling and
  emptying
• To compensate, they have moist skin with
  embedded blood vessels
• CO2 released and O2 absorbed by diffusion across
  semi-permeable membrane (i.e., water layer).
• Semi-permeable membrane necessary for
  concentration gradient that directs movement of
  CO2 released and O2.

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The Living Orders of Amphibians

• Gymnophiona
• Salientia
• Caudata

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Order Gymnophiona(aka, Caecilians)

• 162 species
• Limbless
• Up to 1.5 m long
• Tentacle between eye and nostril sensory organ
• Oviparous and viviparous

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Global Distribution of Gymnophiona
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Gymnophiona Life History, Reproduction, and
Ecology

• We dont know much
• Extended breeding in tropics, across multiple
  seasons
• Primarily fossorial, but also aquatic

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Order Salientia

• 3438 species!!
• No scientific distinction between frogs and
  toads
• Frogs are typically smooth-skinned, have long
  hind limbs for leaping, and live in or near water
• Toads have warty, drier skin, with shorter hind
  limbs , and live on land but most still return
  to water to breed

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Global Distribution of Salientia
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Mechanics of Reproduction in Salientia

• Amplexus
• External fertilization

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Salientia Life History and Reproduction

• Tropics
• Reproduction throughout year, with rainfall as
  the primary cue
• Need water, but not necessarily ponds / streams
• High diversity of reproductive strategies

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Gastric Brooding FrogRheobatrachus vitellinus
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Poison Dart FrogsFamily Dendrobatidae
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Borneo Tree-Hole FrogMetaphrynella sundana
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Salientia Life History and Reproduction

• Temperate Zone
• Reproduction is seasonal and dependent on
  combination of temperature and rainfall
• Generally happens in ponds and lakes
• Explosive (i.e., during brief period of time)

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Salientia Life History and Reproduction
Explosive Breeding
Tadpoles scape algae and diatoms from substrate
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Salientia Ecology Environmental Controls on
Larval Development and Survival

• Hydroperiod
• Canopy cover
• Phenotypic plasticity

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Salientia Ecology Environmental Controls on
Larval Development and Survival

• Hydroperiod

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Hydroperiod

• Period of time a pond had standing water
• Species often matched to particular hydroperiods,
  ranging from days to permanent
• Adaptation to hydroperiod often represents a
  trade-off

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The Hydroperiod Trade-Off

• Long
• High competition / predation
• Slow development

• Short
• Low competition / predation
• Fast development

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Hydroperiod as Primary Filter of Amphibian
Community
Adults
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Salientia Ecology Environmental Controls on
Larval Development and Survival

• Hydroperiod
• Canopy cover

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Canopy Cover

• Affects light regime
• Affects temperature regime
• Affects algal community, abundance, and
  composition

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Yale Forest
(Skelly et al., 2002)
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Whole Pond Experiment

• Manipulate Canopy in 7 Wetlands
• Monitor Population Community Responses

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Canopy Experiment Species
Wood Frog Rana sylvatica
Spring Peeper Pseudacris crucifer
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Forest Canopy and Larval Performance
Open Canopy
Wood Frog
Spring Peeper
Closed Canopy
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Salientia Ecology Environmental Controls on
Larval Development and Survival

• Hydroperiod
• Canopy cover
• Phenotypic plasticity

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Phenotypic Plasticity

• Developmental rates often fine-tuned to avoid
  other species that use the pond (i.e.,
  competitors and predators)
• Tadpoles of some species can change shape to
  increase survival or development rate in pools
  when stuck with predators or too many competitors
• Phenotypic plasticity Ability to activate
  different phenotypes in response to environment

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Response to Predators

• Can fine-tune to respond to multiple predators
• Often reversible

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Environmental Cues

• Predator chemicals
• Dead conspecifics
• Dead heterospecifics

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Response to Competition

• Reduce investment in tail to accelerate
  metamorphosis
• Experiments control for food availability

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Salientia Ecology Some cool exceptions

• Foothills yellow-legged frog
• Tailed frog

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Stream-breeding frogs in North America

• Foothills yellow-legged frog (Rana boylii)
• Sarah Kupferberg studied breeding sites along Eel
  River, northern CA
• Timed egg-laying to avoid fluctuations in river
  stage and current velocity
• Attached eggs to stable substrate (i.e., cobbles
  and boulders)
• Selected wide, shallow reaches where depth would
  not change with discharge.

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Stream-breeding frogs in North America

• Rocky Mountain Tailed Frog (Ascaphus montanus)
• Found in small (1st - 3rd order), cold streams in
  the northern Rockies
• Males dont call
• Internal fertilization with cloacal tail
• Lay eggs under rocks
• Tadpoles develop for 3 yrs. suck onto rocks
  with mouth, scrape off diatoms and insect larvae
• Adults in stream during day, forage along bank at
  night

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Order Caudata

• 352 species
• North America is home to greatest diversity!

Salamandridae
Cryptobranchidae
Hynobiidae
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Global Distribution of Caudata
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Caudata Life History, Reproduction, and Ecology

• Ambystomatidae (30 species)
• Plethodontidae (376 species)

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Ambystomatid Characteristics

• 30 species
• Stout-bodied with short, rounded heads and
  conspicuous costal grooves
• Larvae have broad heads and 3 pairs of bushy
  gills
• Referred to as mole salamanders

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Ambystomatid Life History and Reproduction

• Mostly pond breeders with annual reproductive
  cycle
• Breed in spring, initiated by saturation of
  ground with melting snow and spring rains
• Males and females travel from uplands to
  congregate at semi-permanent to permanent pools

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The Mechanics of Reproduction in Ambystomatids

• Males deposit spermatophores, then females pick
  up with cloaca
• Females attach eggs to substrate sticks, logs,
  rocks
• Larval development highly variable weeks,
  months, multiple years in stable habitats

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Stream-Breeding Ambystomatid
Ambystoma barbouri Streamside salamander
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An Alternative Cycle
Ambystoma opacum (Marbled salamander)

• Mate on land in fall
• Female selects nest site in dry or partially-dry
  bed of temporary pond
• Make nest by burrowing cavities in ground
• Embryos hatch within 1-2 days after nest
  submerged in spring

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An Alternative Cycle
Ambystoma opacum (Marbled salamander)
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Ambystomatid Ecology

• Neoteny and Cannibalism
• Unisexual Populations

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Ambystomatid Ecology

• Neoteny and Cannibalism

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Ambystomatid Ecology Neoteny and Cannibalism
Ambystoma tigrinum
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Neoteny Retention of larval characteristics in
mature adults (aka, facultative metamorphosis)

• In cold, high-elevation ponds in CO, also in
  springs and cattle tanks in Mexico
• Favored in stable and productive habitats, or
  where low temps constrain full metamorphosis
• See this in other salamanders too, especially
  cave species

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Neoteny
Family Proteidae Proteus anguinus
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• Cannibalism
• 2 larval morphotypes in A. tigrinum
• Normal eats invertebrates and zooplankton
• Cannibal eats other salamander larvae

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Ambystomatid Ecology

• Neoteny and Cannibalism
• Unisexual Populations

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Ambystomatid Ecology Unisexual Populations

• Almost entirely female
• New England, Great Lakes and Canadian Maritimes
• Hybrids of 4 species
• Single individual can have genetic components of
  3 species (i.e., triploid, 3N)

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A. laterale
A. jeffersonianum
A. texanum
A. tigrinum
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Unisexual Ambystomatid populations

• Reproduce by gynogenesis and syngamy
• Reconstituted diploids (2N) dont survive, but
  need diploid males for reproduction
• Males supplied by immigration, or through
  successful reproduction with subpopulation of
  diploid females
• Believed to be result of past hybridization

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Plethodontid Characteristics

• 376 species
• LunglessWHY?
• Nasolabial grooves
• Males get cirri when sexually active
• Terrestrial and stream-associated

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Plethodontid Life History and Reproduction

• Biennial cycle (once every 2 years)
• Active at surface in forests and along streams
  from late spring to autumn
• Mating in late summer and autumn
• Oviposition in spring and early summer
• Most species have aquatic larvae and terrestrial
  adults, but some are only terrestrial.

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Crazy Plethodontid Courtship
Male ID sex and species via chemoreception
Male initiates tail-straddle walk, which can go
on for minutes to hours!
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Crazy Plethodontid Courtship

• Male uses cirri and head slap to deliver
  mental-gland secretions to female.

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Plethodontid Egg Sites and Parental Guarding
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Plethodontid Distribution and Diversity Southern
Appalachians

• Highest diversity in Southern Appalachians
• Southern Appalachians are geologically stable
• Diversity decreases moving northward
• Especially diverse stream salamander communities
  in Southern Appalachians

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Early species radiation among stream types
Ephemeral
Springs
Perennial
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Lateral Habitat Partitioning in Southern App.
Plethodontids
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Lateral Habitat Partitioning in Southern App.
Plethodontids
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Plethodontid Distribution and Diversity Central
America

• Second highest diversity in Central America
• Central America is geologically active
• Species are distributed along elevational
  gradient

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Distribution along Elevational Gradient
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Vertical Habitat Partitioning in Central American
Plethodontids