In-Depth Notes on Class Amphibia

Overview of Class Amphibia

  • Amphibia represents a critical class within the phylum Chordata, distinguished by their dual life stages: aquatic larvae and terrestrial adults.

Phylogeny of Chordates

  • Ancestral Deuterostome: The common ancestor of chordates.

  • Key Features of Chordates:

    • Notochord

    • Vertebrae

    • Jaws and mineralized skeleton

    • Lungs or lung derivatives

    • Lobed fins

    • Limbs with digits

  • Major Clades:

    • Echinodermata (sister group to chordates)

    • Subphylum Cephalochordata (lancelets)

    • Subphylum Urochordata (tunicates)

    • Superclass Myxini (hagfishes)

    • Superclass Petromyzontida (lampreys)

    • Class Chondrichthyes (sharks, rays, chimaeras)

    • Class Actinopterygii (ray-finned fishes)

    • Class Actinistia (coelacanths)

    • Class Dipnoi (lungfishes)

    • Class Amphibia

    • Class Reptilia (including turtles, snakes, crocodiles, birds)

    • Class Mammalia (mammals)

Amphibian Diversity

  • Three Major Clades:

    • Order Gymnophiona (Apoda): Caecilians

    • Legless, burrowing amphibians not found in BC.

    • Order Anura: Frogs and toads

    • Tailless, with 12 species found in BC.

    • Primarily external fertilization.

    • Order Caudata: Salamanders and newts

    • Tailed, with 9 species reported in BC.

    • Primarily internal fertilization.

  • Global species count: 49 families, ~5,800 species (~41% threatened by extinction, source: IUCN 2011).

Key Characteristics of Amphibians

  • Physical Traits:

    • Lacks fur, scales, feathers, claws, or beaks.

    • Skin is highly permeable to water and gases, necessitating moist environments.

    • Ectothermic (cold-blooded), relying on environmental temperature for body heat regulation.

  • Reproductive Features:

    • Non-amniotic eggs that require water or moist conditions for development.

    • Various reproductive methods:

    • External vs. internal fertilization

    • Oviparous, ovoviviparous, or viviparous development.

Breathing Mechanisms

  • Frogs breathe using:

    • Gills during larval stages

    • Lungs during adult stages

    • Skin for gas exchange (transcutaneous breathing).

  • Certain species, like the Western Red-backed Salamander, can also utilize skin for breathing (lungless).

Metamorphosis

  • Life Cycle:

    • Typically involves an aquatic larva transforming into a terrestrial adult.

    • Some exhibit neoteny, retaining juvenile features while becoming sexually mature.

    • Example species with no aquatic phase:

    • Western Red-backed Salamander, Coeur d’Alene Salamander.

Behavioral Adaptations and Parental Care

  • Many amphibians exhibit unique mating rituals and calls.

  • Parental care occurs in some salamanders, while frogs generally do not show this behavior.

  • Notable examples include:

    • Brood piracy among salamanders.

    • African Bull Frogs demonstrate problem-solving abilities in parental care.

Ecology and Conservation

  • Habitat diversity includes aquatic (ponds, lakes, streams) and terrestrial (moist woods, desert breeding ponds).

  • Amphibians are crucial links in food webs, playing roles as both predator and prey.

  • Global concerns:

    • Habitat loss, introduced species, pollution, and diseases (e.g., chytridiomycosis).

Amphibians of British Columbia

  • Local Species:

    • Boreal Chorus Frog: Found in Omineca and Peace; status: Yellow (of concern).

    • Bullfrog: Exotic species found in Vancouver Island and Lower Mainland. Amphibia, a class in the phylum Chordata, includes diverse species that undergo metamorphosis. Major clades encompass Echinodermata, Cephalochordata, Urochordata, Myxini, Petromyzontida, Chondrichthyes, Actinopterygii, Actinistia, Dipnoi, Reptilia, and Mammalia. Key amphibian features include: - **Diversity**: Three major orders: Gymnophiona (caecilians), Anura (frogs and toads), and Caudata (salamanders and newts). - Gymnophiona: Legless, not in BC. - Anura: 12-tailed species in BC, mainly external fertilization. - Caudata: 9 species in BC, primarily internal fertilization. Global count: ~5,800 species, with ~41% threatened. - **Characteristics**: No fur, scales, or claws; skin is permeable, requiring moisture; ectothermic; eggs need a moist environment for development with various reproductive methods. - **Breathing**: Larval frogs use gills, adults use lungs and skin. - **Metamorphosis**: Changes from aquatic larvae to terrestrial adults, some species retaining juvenile features. - **Behavior**: Unique mating rituals, parental care seen in some salamanders. - **Ecological Role**: Important in food webs; face threats from habitat loss, pollution, and diseases. - **BC Species**: Boreal Chorus Frog (Yellow status of concern).

    • Northern Leopard Frog: Endangered status in BC; recognized by its distinct rings.

    • Pacific Tree Frog: Notable for its size and climbing adaptations.

Summary

  • Amphibians are diverse vertebrates with unique adaptations to their environments, facing numerous challenges that threaten their existence. Conservation efforts are crucial to preserve the diverse amphibian populations in regions like British Columbia.