Diversity of Living Amphibians and Reptiles

Modern Reptiles and Amphibians

• Modern reptiles and amphibians are not sister taxa.

• Historically, they have been confused and studied together because they are often found in similar habitats.

• Linnaeus (1758), the father of biological nomenclature and classification, described them as "the worst and most horrible of animals," highlighting their cold bodies, dirty complexion, foul skin, grim faces, brooding gaze, foul smell, hoarse voice, squalid habitats, and horrible poison.

Differences between Amphibians and Reptiles

Amphibians

• Egg: Shell-less, non-amniote egg, requiring water for reproduction.

• Larval Stage: Often have a larval stage.

• Skin: Moist skin plays a major role in gas exchange.

• Habitat: Diverse mostly in humid habitats.

• Keratinous Structures: Lack keratinous structures.

Reptiles

• Egg: Shelled amniote egg, self-contained and independent of water.

• Larval Stage: No larval stage.

• Skin: Dry skin with little role in gas exchange.

• Habitat: Often successful in dry habitats.

• Skin: Covered in scales, often with complex structures.

Features of Living Amphibians

• Live on land and water (amphi = both, bios = life).

• Reproduction often tied to water: aquatic larval life stage followed by metamorphosis. However, there are many exceptions, which will be discussed in later lectures.

• Skin is moist and generally permeable, which is important for gas exchange but also makes them vulnerable to water loss.

• Most species are tied to humid environments, with the greatest diversity in tropical forests.

• Species inhabiting dry areas shelter in humid microhabitats and are often inactive for most of the year.

Diversity of Living Amphibians

• Three major groups:

  • Anura – frogs and toads – 7806 species

  • Caudata – salamanders and newts – 826 species

  • Gymnophiona – caecilians – 225 species

Gymnophiona - Caecilians

• Limbless, burrowing amphibians.

• Mostly small, a few species grow to > 100 cm.

• Distribution: tropics, worldwide excluding Australia.

• Fossorial or aquatic.

• Live-bearing or egg-laying.

• Feed on invertebrates.

• Reduced or absent eyes.

• Unique sensory tentacles.

• Often pronounced parental care.

Unique Features of Caecilians

• Hydrostatic "tube in a tube" movement, unique in vertebrates, which generates greater forward force than standard longitudinal muscles.

• Fossoriality: constraint on head size.

• Large muscle and posterior projection of the mandible ensure adequate bite force.

• Maternal nutrition for offspring: Skin feeding in oviparous Boulengerula taitanus.

• Parental care of oviparous Siphonops annulatus includes cloacal "milk" secretion that supplements skin feeding.

Caudata – Newts and Salamanders

• Limbed (usually), tailed amphibians.

• Mostly small, some up to ~ 100 cm.

• Terrestrial or aquatic, few arboreal.

• Distribution: worldwide except Africa, Australia.

Evolutionary Trends

Family Plethodontidae – lungless salamanders – contains 67% of Caudata

*   Lunglessness – more than 50% of caudates are functionally lungless, breathing through skin only.
*   Paedomorphosis – retention of larval characters in adults – e.g. permanent aquatic life, gills; evolved multiple times.

UK Species

• Triturus cristatus – Great crested newt

• Lissotriton vulgaris – Smooth newt

• Lissotriton helveticus – Palmate newt

Palmate Newt – Lissotriton helveticus

• Smallest UK newt – to 9 cm.

• Most common in north and west of UK.

• Most common newt in montane and acid soil areas – including much of NW Wales.

• Common in Bangor and on Anglesey (e.g., Treborth, Newborough Forest, throughout Snowdonia).

• Male: black, enlarged feet; tail filament; Both sexes: pinkish unspotted throat

Smooth Newt – Lissotriton vulgaris

• Small – to 10 cm

• Most common in Midlands and eastern England

• Rarer in northern and western hill and acid soil areas

• Very uncommon in NW Wales – often confused with palmate newt. Only reliable records from NE Wales W. to Llandudno

• Males: wavy crest, strongly spotted, feet not black, no tail filament. Both sexes: Throat yellow, clearly spotted

Great Crested Newt – Triturus cristatus

• UK’s largest newt – to 18 cm

• Most common in Midlands and eastern England

• Rarer in northern and western hill and acid soil areas

• Common on Anglesey (e.g., Newborough Forest), a few colonies along mainland coasts (Llanfairfechan, Pensychnant)

• Males: high, jagged crest. Females: no crest. Rough, warty skin. Males: silver “flash” on tail

• European Protected Species

  • Licence required to:

    • Disturb (including torchlight surveys!)

    • Handle

  • Habitats also protected

  • Hence: developers’ nemesis!

  • Delays could be avoided by taking ecology seriously from the start…

Anura – Frogs and Toads

• Tail-less amphibians with large heads, short bodies, well-developed limbs.

• Worldwide distribution.

• Extensive ecological and reproductive diversity.

• 88% of total amphibian diversity!

• Note: “frogs” and “toads” are not a natural evolutionary subdivision!

• “Frogs” (Ranidae), “Toads” (Bufonidae)

Important Morphological/Ecological Trends

• Arboreality, e.g. family Hylidae (tree frogs) – long fore- and hind limbs

• Burrowing (short limbs & snout) – various families, evolved multiple times

• Aquatic – long hind limbs, large webbed feet

• Jumping vs hopping/walking – long muscular hind limbs vs short hind limbs

• Toxic skin secretions +/-aposematic coloration

  • Dendrobatidae – C&S America

  • Mantella - Madagascar
    Bufo marinus – cane toad

• Key role of acoustic communication

• Diversity of modes of reproduction, usually involving shift away from water

  • Marsupial frog (Flectonotus sp.) incubates eggs under the skin of the back; the female then deposits tadpoles in the water.

  • Foam nest-building frogs avoid the need to deposit eggs in water.

UK Species

• Rana temporaria – Common frog

• Bufo bufo – Common toad

• Epidalea calamita - Natterjack

• Pelophylax lessonae – Pool Frog

Common Frog – Rana temporaria

• Widespread throughout Britain and Ireland, to over 1000 metres elevation.

• Remains common in gardens and the wider countryside.

• Breeds January – March.

• Eggs laid in clumps of spawn.

• Dark ear patch / mask

Common Toad – Bufo bufo

• Widespread throughout Britain, absent from Ireland.

• Widespread in Europe and western Asia.

• Declining severely in the UK and other parts of Europe.

• Breeds Feb-March in UK, depending on region

• Explosive breeder

• Spawn laid in strings

Natterjack Toad – Epidalea calamita

• Localised in Britain and SW Ireland

• Found in heathlands and dune ponds; often breed in brackish water.

• In severe decline

• European Protected Species

• light line along spine

Pool Frog – Pelophylax lessonae

• UK populations were long believed to be introduced from C. Europe

• Usually found in and around permanent pools – noisy!

• The last population in East Anglia died out in the 1990s

• Shortly thereafter, identified as having been native after all! (DNA, sound analysis)

• Now being reintroduced from Sweden to Norfolk.