– 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.

“ 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

• Kingdom: Animalia
• Phylum: Chordata
• Class: Amphibia

• 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.

Costs and Benefits?

– Support and locomotion
– Respiration

• 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

• Lungs, but no efficient way of filling and emptying
• To compensate, they have moist skin with embedded blood vessels
• CO
2 released and O
2 absorbed by diffusion across semi-permeable membrane (i.e., water layer).
• Semi-permeable membrane necessary for concentration gradient that “ directs ” movement of
CO
2 released and O
2
.

– Gymnophiona
– Salientia
– Caudata

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

– We don ’ t know much
– Extended breeding in tropics, across multiple seasons
– Primarily fossorial, but also aquatic

– 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

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

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

Short
• Low competition / predation
• Fast development
Long
• High competition / predation
• 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

(Skelly et al., 2002)

• Manipulate Canopy in 7 Wetlands
• Monitor Population & Community Responses

Wood Frog
Rana sylvatica
Spring Peeper
Pseudacris crucifer

Open
Canopy
Spring
Peeper
Wood
Frog
• Light
• Temperature
• DO
2
• Periphyton
Closed
Canopy

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

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

Environmental Cues
• Predator chemicals
• Dead conspecifics
• Dead heterospecifics

• 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 (1 st - 3 rd 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

–
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

: 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

Family Proteidae
Proteus anguinus

• 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. jeffersonianum
A. tigrinum 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