Exploring Amphibians: Taxonomy, Evolution, and Environment

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 O2absorbed 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 don’t 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. Sp.Y Sp.X Hydroperiod Larvae Other Conditions Metamorphosis 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. Light • Temperature • DO2 • Periphyton Forest Canopy and Larval Performance Open Canopy Spring Peeper Wood Frog 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 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

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

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)