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.

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: splay-legged 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 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

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 Low competition / predation Fast development Long High competition / predation Slow development

Hydroperiod as Primary “Filter” of Amphibian Community Adults Hydroperiod Sp.X Sp.Y Metamorphosis Other Conditions Larvae

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 Photos are of the same pond before and after overstory removal along S shore. Enclosures are shown in left hand photo. White pvc pipe in foreground of left hand photo can be seen sticking out of ice in lower right of right hand photo.

Canopy Experiment Species Photos are of the same pond before and after overstory removal along S shore. Enclosures are shown in left hand photo. White pvc pipe in foreground of left hand photo can be seen sticking out of ice in lower right of right hand photo. Wood Frog Rana sylvatica Spring Peeper Pseudacris crucifer

Forest Canopy and Larval Performance Open Canopy Spring Peeper Wood Frog Light Temperature DO2 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

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 Salamandridae Cryptobranchidae Hynobiidae North America is home to greatest diversity! Salamandridae Cryptobranchidae Hynobiidae

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 semi-permanent 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 Streamside salamander 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. 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