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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 ... – PowerPoint PPT presentation

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Title: Amphibians!


1
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.

2
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

3
Amphibian Taxonomy
  • Kingdom Animalia
  • Phylum Chordata
  • Class Amphibia

4
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.

5
The Complex Life Cycle
Costs and Benefits?
6
Major Challenges of Life on Land
  • Support and locomotion
  • Respiration

7
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

8
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.

9
The Living Orders of Amphibians
  • Gymnophiona
  • Salientia
  • Caudata

10
Order Gymnophiona(aka, Caecilians)
  • 162 species
  • Limbless
  • Up to 1.5 m long
  • Tentacle between eye and nostril sensory organ
  • Oviparous and viviparous

11
Global Distribution of Gymnophiona
12
Gymnophiona Life History, Reproduction, and
Ecology
  • We dont know much
  • Extended breeding in tropics, across multiple
    seasons
  • Primarily fossorial, but also aquatic

13
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

14
Global Distribution of Salientia
15
Mechanics of Reproduction in Salientia
  • Amplexus
  • External fertilization

16
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

17
Gastric Brooding FrogRheobatrachus vitellinus
18
Poison Dart FrogsFamily Dendrobatidae
19
Borneo Tree-Hole FrogMetaphrynella sundana
20
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)

21
Salientia Life History and Reproduction
Explosive Breeding
Tadpoles scape algae and diatoms from substrate
22
Salientia Ecology Environmental Controls on
Larval Development and Survival
  • Hydroperiod
  • Canopy cover
  • Phenotypic plasticity

23
Salientia Ecology Environmental Controls on
Larval Development and Survival
  • Hydroperiod

24
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

25
The Hydroperiod Trade-Off
  • Long
  • High competition / predation
  • Slow development
  • Short
  • Low competition / predation
  • Fast development

26
Hydroperiod as Primary Filter of Amphibian
Community
Adults
27
Salientia Ecology Environmental Controls on
Larval Development and Survival
  • Hydroperiod
  • Canopy cover

28
Canopy Cover
  • Affects light regime
  • Affects temperature regime
  • Affects algal community, abundance, and
    composition

29
Yale Forest
(Skelly et al., 2002)
30
Whole Pond Experiment
  • Manipulate Canopy in 7 Wetlands
  • Monitor Population Community Responses

31
Canopy Experiment Species
Wood Frog Rana sylvatica
Spring Peeper Pseudacris crucifer
32
Forest Canopy and Larval Performance
Open Canopy
Wood Frog
Spring Peeper
Closed Canopy
33
Salientia Ecology Environmental Controls on
Larval Development and Survival
  • Hydroperiod
  • Canopy cover
  • Phenotypic plasticity

34
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

35
Response to Predators
  • Can fine-tune to respond to multiple predators
  • Often reversible

36
Environmental Cues
  • Predator chemicals
  • Dead conspecifics
  • Dead heterospecifics

37
Response to Competition
  • Reduce investment in tail to accelerate
    metamorphosis
  • Experiments control for food availability

38
Salientia Ecology Some cool exceptions
  • Foothills yellow-legged frog
  • Tailed frog

39
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.

40
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

41
Order Caudata
  • 352 species
  • North America is home to greatest diversity!

Salamandridae
Cryptobranchidae
Hynobiidae
42
Global Distribution of Caudata
43
Caudata Life History, Reproduction, and Ecology
  • Ambystomatidae (30 species)
  • Plethodontidae (376 species)

44
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

45
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

46
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47
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

48
Stream-Breeding Ambystomatid
Ambystoma barbouri Streamside salamander
49
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

50
An Alternative Cycle
Ambystoma opacum (Marbled salamander)
51
Ambystomatid Ecology
  • Neoteny and Cannibalism
  • Unisexual Populations

52
Ambystomatid Ecology
  • Neoteny and Cannibalism

53
Ambystomatid Ecology Neoteny and Cannibalism
Ambystoma tigrinum
54
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

55
Neoteny
Family Proteidae Proteus anguinus
56
  • Cannibalism
  • 2 larval morphotypes in A. tigrinum
  • Normal eats invertebrates and zooplankton
  • Cannibal eats other salamander larvae

57
Ambystomatid Ecology
  • Neoteny and Cannibalism
  • Unisexual Populations

58
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)

59
A. laterale
A. jeffersonianum
A. texanum
A. tigrinum
60
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

61
Plethodontid Characteristics
  • 376 species
  • LunglessWHY?
  • Nasolabial grooves
  • Males get cirri when sexually active
  • Terrestrial and stream-associated

62
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.

63
Crazy Plethodontid Courtship
Male ID sex and species via chemoreception
Male initiates tail-straddle walk, which can go
on for minutes to hours!
64
Crazy Plethodontid Courtship
  • Male uses cirri and head slap to deliver
    mental-gland secretions to female.

65
Plethodontid Egg Sites and Parental Guarding
66
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

67
Early species radiation among stream types
Ephemeral
Springs
Perennial
68
Lateral Habitat Partitioning in Southern App.
Plethodontids
69
Lateral Habitat Partitioning in Southern App.
Plethodontids
70
Plethodontid Distribution and Diversity Central
America
  • Second highest diversity in Central America
  • Central America is geologically active
  • Species are distributed along elevational
    gradient

71
Distribution along Elevational Gradient
72
Vertical Habitat Partitioning in Central American
Plethodontids
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