Amphibians Lecture RNR 3018

General characteristics of amphibians:

• Glandular skin produces toxins and mucous

• True middle ear with columella for hearing

• One neck vertebra

• Lack of dermal bone and claws

• Eggs vulnerable to drying out

• Varied respiration methods (lungs, gills, skin)

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• Amphibian classification:

  • Caecilians, Salamanders, and Frogs

  • Various families and species within each group

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Amphibian diversity:

• Highest in wet tropical and temperate forests

• 135 species listed on Biodiversity Mapping.org

Class Amphibia Order Gymnophiona (Caecilians):

• 184 species globally, mainly tropical

• Unique characteristics and behavior

• Evolutionary history related to continental drift

• They evolved on the Pangea supercontinent before it broke up ~225 mya

Class Amphibia Order Caudata (Salamanders and Newts):

• 578 species worldwide

  • 6 families, 23 taxa in LA

  • 102 spp. in SE US (17% of the world’s species

• Diverged about 230 million years ago

  • Pre-date dinosaurs by 40 million years

• Move with lateral undulation

  • Aided by limbs, especially in adults

Caudata distribution:

• Salamanders absent from tropics but include species in most of the northern temperate zone

• Diversified in Laurasia and later moved to South America

Salamander skeleton features:

• Short neck (1 vertebra)

• Short ribs along entire trunk

• Little modification for attachment of pelvis to vertebral column
  

Salamander Vocabulary

• Nasolabial Grooves

• Costal Grooves

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Ambystomatidae - mole salamanders

• Endemic to North America

• 5 species in LA (~32 total)

• Adults with lungs

• Mate and oviposit on land

• Breed around temporary ponds

• Aquatic larvae with external gills

• Includes some all female populations!

• No nasolabial grooves

• Ambystomid larva- all have three pairs of external gills and a large caudal fin

Amphiumidae - Amphiumas

• 2 species in LA

• Aquatic

• Nocturnal

• Reduced pelvic and pectoral girdles and vestigial limbs

• Adults have lungs and a single pair of gill slits

Three-toed Amphiuma – Amphiuma tridactylum

• Use semi-permanent to permanently flooded swamps, sloughs, and ditches

• Active at night; in burrow during day

• Eat crawfish, earthworms, fish, and inverts

Plethodontidae – lungless salamanders

• Largest family (27 genera; 240 spp. worldwide, 12 spp. in LA)

• No lungs or gills in adults

• Nasolabial grooves

• Tail round in cross section

• Active in leaf litter all year

• Many can project tongue

Proteidae – Mudpuppies

• 2 species in LA

• Aquatic

• Paedomorphic (like many salamanders)

  • Adults retain larval traits associated with water:

  • External gills, short limbs, laterally compressed tail

Salamandridae - Newts

• 1 species in LA

• Lack nasolabial grooves and distinct costal grooves

• Terrestrial juveniles, aquatic adults

• Often bright (toxic) coloration

Sirenidae (Sirens):

• 1 species in LA

• Aquatic

• Laterally compressed tail

• External gills

• No rear legs or pelvic girdle

Cryptobranchidae (Huge Salamanders):

• Not found in LA

Order Anura: Frogs and Toads

• Order Anura includes various families and species of frogs and toads

  • Total >5000 species in 29 families with different species like salamanders, frogs, and toads

  • 31 species, 6 families in LA

Distribution of Anura

• Anura distribution is prominent in Neotropical wet forests, especially in Brazil

  • Brazil alone hosts around 1000 species of amphibians, mostly frogs

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• 6 frog families in LA represent much of the frog diversity

  • Notable families include Spadefoot, Treefrogs, Toads, Greenhouse, Chirping Spadefoots, Ranids, and more

Frog skeleton and metamorphosis

• Adult frog skeleton modified from the amphibian plan-

  • Much reduced trunk

  • No tail

  • Modified pelvis and hindlimb

Frog reproductive phenology in LA

• Why is this so well known?

• Frogs call! Vocal, rather than chemical, communication is critical in anurans compared to salamanders

  • Taxonomy changes may affect the naming of species like Spring Peeper

Bufonidae - True toads

• 500 species, 5 in LA

• Strongly glandular skin; can be toxic to predators

• No teeth

• Aquatic larvae (usually), terrestrial adults

Hylidae: Treefrogs and other Hylids

• Over 700 species worldwide, 15 in LA

• Most have toepads

• Some are arboreal

• Strongly visual- often brightly colored

Eleutherodactylidae - Southern frogs or rain frogs

• 1300 species, 2 species introduced to LA (see the forum for distinguishing the two species)

• Exclusively Neotropical

• No webbing or toe discs

• Foam nests, some with direct development (going from egg to tadpole to frog before hatching)

Microhylidae – Narrow-mouthed frogs

• 50 species, 1 in LA

• Not a toad or a hylid- related to ranids

• No tympanum

• Some with direct development or other mechanisms to avoid water

• Feed on ants; protected by toxic skin secretions •

• Fun fact- they walk rather than hop

Ranidae- True Frogs

• About 700 species worldwide, 7 species in LA

• Free-swimming tadpoles

• Adults generally terrestrial and aquatic

• LA species formerly in genus Rana
  

Scaphiopodidae (spadefoots)

• 7 North American species, sometimes lumped with ~150 Old World species

• Terrestrial, even subterranean adults

• Breed in shallow water, rapid larval growth

• Unique hardened spade on hind foot

Declines and Extinctions

• More species threatened than reptiles, birds, or mammals

  • 1,856 sp (32.5%) threatened

  • 43% decreasing, 1% increasing, 27% stable

• Causes:

  • Habitat loss/degradation

  • Overexploitation

  • Environmental contaminants

  • Climate change

  • Chytrid fungus & other diseases