Download Amphibians!

Amphibians!
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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.
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
Amphibian Taxonomy
•
Kingdom: Animalia
•
Phylum: Chordata
•
Class: Amphibia
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.
The Complex Life Cycle
Costs and Benefits?
Major Challenges of Life on Land
– Support and locomotion
– Respiration
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: splaylegged instead of legs
rotated beneath body
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.
The Living Orders of Amphibians
– Gymnophiona
– Salientia
– Caudata
Order Gymnophiona
(aka, Caecilians)
– 162 species
– Limbless
– Up to 1.5 m long
– Tentacle between eye and nostril – sensory organ
– Oviparous and viviparous
Global Distribution of Gymnophiona
Gymnophiona Life History,
Reproduction, and Ecology
– We don’t know much
– Extended breeding in tropics,
across multiple seasons
– Primarily fossorial, but also
aquatic
Order Salientia
– 3438 species!!
– No scientific distinction
between frogs and toads
– Frogs are typically smoothskinned, 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
Global Distribution of Salientia
Mechanics of Reproduction in Salientia
• Amplexus
• External fertilization
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
Gastric Brooding Frog
Rheobatrachus vitellinus
Poison Dart Frogs
Family Dendrobatidae
Borneo Tree-Hole Frog
Metaphrynella sundana
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)
Salientia Life History and Reproduction
Explosive Breeding
Tadpoles scape algae and
diatoms from substrate
Salientia Ecology: Environmental Controls on
Larval Development and Survival
• Hydroperiod
• Canopy cover
• Phenotypic plasticity
Salientia Ecology: Environmental Controls on
Larval Development and Survival
• Hydroperiod
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
The Hydroperiod Trade-Off
Short
Long
• Low competition / predation
• High competition / predation
• Fast development
• Slow development
Adults
Hydroperiod as Primary “Filter” of
Amphibian Community
Sp.X
Sp.Y
Hydroperiod
Larvae
Other
Conditions
Metamorphosis
Salientia Ecology: Environmental Controls on
Larval Development and Survival
• Hydroperiod
• Canopy cover
Canopy Cover
•
Affects light regime
•
Affects temperature regime
•
Affects algal community, abundance, and composition
Yale Forest
(Skelly et al., 2002)
Whole Pond Experiment
• Manipulate Canopy in 7 Wetlands
• Monitor Population & Community Responses
Canopy Experiment Species
Wood Frog
Spring Peeper
Rana sylvatica
Pseudacris crucifer
Forest Canopy and Larval Performance
Open
Canopy
Spring
Peeper
Wood
Frog
• Light
• Temperature
• DO2
Closed
Canopy
• Periphyton
Salientia Ecology: Environmental Controls on
Larval Development and Survival
• Hydroperiod
• Canopy cover
• Phenotypic plasticity
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
Response to Predators
• Can fine-tune to respond to multiple predators
• Often reversible
Environmental Cues
• Predator chemicals
• Dead conspecifics
• Dead heterospecifics
Response to
Competition
• Reduce investment in tail to accelerate metamorphosis
• Experiments control for food availability
Salientia Ecology:
Some cool exceptions
• Foothills yellow-legged frog
• Tailed frog
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.
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 don’t 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
Order
Caudata
– 352 species
– North America is home to
greatest diversity!
Salamandridae
Hynobiidae
Cryptobranchidae
Global Distribution of Caudata
Caudata Life History, Reproduction, and
Ecology
• Ambystomatidae (30 species)
• Plethodontidae (376 species)
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”
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 semipermanent to permanent pools
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
Stream-Breeding Ambystomatid
Ambystoma barbouri
Streamside salamander
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
An Alternative Cycle
Ambystoma opacum
(Marbled salamander)
Ambystomatid Ecology
• Neoteny and Cannibalism
• Unisexual Populations
Ambystomatid Ecology
• Neoteny and Cannibalism
Ambystomatid Ecology:
Neoteny and Cannibalism
Ambystoma tigrinum
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
Neoteny
Family Proteidae
Proteus anguinus
Cannibalism
• 2 larval morphotypes in A. tigrinum
• Normal eats invertebrates and zooplankton
• Cannibal eats other salamander larvae
Ambystomatid Ecology
• Neoteny and Cannibalism
• Unisexual Populations
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)
A. laterale
A. tigrinum
A. jeffersonianum
A. texanum
Unisexual Ambystomatid populations
• Reproduce by gynogenesis and syngamy
• Reconstituted diploids (2N) don’t 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
Plethodontid
Characteristics
• 376 species
• Lungless…WHY?
• Nasolabial grooves
• Males get cirri when sexually active
• Terrestrial and stream-associated
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.
Crazy
Plethodontid
Courtship
Male ID sex and species
via chemoreception
Male initiates tail-straddle
walk, which can go on for
minutes to hours!
Crazy
Plethodontid
Courtship
• Male uses cirri and
head slap to “deliver”
mental-gland secretions
to female.
Plethodontid Egg Sites and Parental
Guarding
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
Early species radiation among stream types
Ephemeral
Springs
Perennial
Lateral Habitat
Partitioning in
Southern App.
Plethodontids
Lateral Habitat Partitioning in Southern App.
Plethodontids
Plethodontid Distribution and Diversity:
Central America
• Second highest diversity in
Central America
• Central America is
geologically active
• Species are distributed
along elevational gradient
Distribution along Elevational Gradient
Vertical Habitat Partitioning in Central
American Plethodontids