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Amphibians I. BIOL 4270. Amphibian Diversity & Adaptations. Goals: Examine the adaptations that have made amphibians so successful Examine some of the diversity in life histories Examine the characteristics of amphibians that have led to their current distributions

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Amphibians I

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Amphibians I

BIOL 4270


Amphibian Diversity & Adaptations

Goals:

  • Examine the adaptations that have made amphibians so successful

  • Examine some of the diversity in life histories

  • Examine the characteristics of amphibians that have led to their current distributions

  • Discover some of BC’s amphibians

  • Paper discussion


>100 million years of experimentation


Modern Amphibians

3 living amphibian orders, > 6000 species

  • Larvae use ancestral lateral-line systems, but adults use olfactory epithelium to sense airborne odors

  • Ancestral lifestyle

    • eggs aquatic, hatch to form aquatic larvae that use gills for respiration

    • Metamorphosed adults use cutaneous respiration; many have lungs


Alternative example


Derived lifestyles

  • Some salamanders lack a complete metamophosis and retain a permanently aquatic, larval morphology throughout life

  • Some caecilians, frogs, and salamanders live entirely on land and have no aquatic larval phase

  • Some frogs, salamanders, and caecilians metamorphose, but remain in water as adults


Characteristics of Modern Amphibians

  • Skeleton mostly bony – varying numbers of vertebrae; ribs present in some, absent or fused to vertebrae in others


Characteristics of Modern Amphibians

2) Body forms vary greatly among species: salamanders usually have distinct head, neck, trunk and tail; adult frogs have a compressed body with fused head and trunk and no intervening neck; caecilians have an elongated trunk not strongly demarkated from the head and a terminal anus

Wandering salmander, Aneidesvagrans

Coastal tailed frog,

Ascaphustruei

Dermophismexicanus


Characteristics of Modern Amphibians

3) Usually quadrupedalin two pairs associated with shoulder/hip girdle, although some forms have a single pair of limbs and others no limbs (e.g., caecilians); webbed feet often present; no true nails; forelimb usually with four digits, but sometimes five and sometimes fewer

Rough-skinned Newt, Taricha granulose


However….

Blackburn, D.C., Hanken, J. and Jenkins Jr., F.A. 2008. Concealed weapons: erectile claws in African frogs. Biology Letters.


Not surprisingly, the Camaroonians knew about the claws all along…


Characteristics of Modern Amphibians

4) Heart with a sinus venuosus, two atria, one ventricle, conusarteriosus; double circulation through the heart in which pulmonary arteries and veins supply lungs (when present) and return oxygenated blood to heart; skin abundantly supplied with blood vessels.


Characteristics of Modern Amphibians

5) Skin smooth, moist, and glandular; integument modified for cutaneous respiration; pigment cells (chromatophors) common and of considerable variety; granular glands associated with secretion of defense compounds

Photomicrograph of stomach skin from Ranatemporaria


Strawberry poison dart frogs (Dendrobatespumillo) – colour variation from different islands in Panama


Rough-skinned Newt (Tarichagranulosa)

Most poisonous BC amphibian

Many dead birds and snakes are found with rough-skinned newts in their stomachs; however, common garter snakes appear unaffected

Newt contains enough poison to kill 25,000 mice

Poison itself is a tetrodotoxin, similar to that created by puffer-fish


Characteristics of Modern Amphibians

6) Respiration by skin and in some forms by gills and/or lungs, presence of gills and lungs varies among species and by developmental stage of some species; forms with aquatic larvae lose gills at metamophosis in frogs; many salamanders retain gills and an aquatic habitat throughout life

Larval tiger salamander, Ambystomatigrinum


Characteristics of Modern Amphibians

7) Ectothermic, body temperature dependent upon environmental temperature and not modulated by metabolically generated heat

Great basin spadefoot toad, Speaintermontana


Characteristics of Modern Amphibians

8) For vision in air, cornea rather than lens is principal refractive surface for bending light; eyelids and lachrymal glands protect and wash eyes


Characteristics of Modern Amphibians

9) Separate sexes; fertilization mostly external in frogs and toads, but internal via a spermatophore in most salamanders and caecilians; predominantly oviparous, some ovivivparous or viviparous; metamorphosis usually present; moderately yolky eggs (mesolecithal) with jellylike membrane coverings


Rain frogs

Even in species that are primarily terrestrial, there is always a strong reliance on water for reproduction.

video


The success stories


Modern Amphibians

Caecilians: Order Gymnophiona (Apoda)

Salamanders: Order Urodela (Caudata)

Frogs and Toads: Order Anura (Salientia)


BC Amphibians

  • 13 species of frogs and toads

  • 9 species of salamander

  • 0 caecilians

Columbia Spotted Frog

Coastal Giant Salamander


Caecilians: Order Gymnophiona (Apoda)

~173 species of elongate, limbless, burrowing creatures

0 in BC


Caecilian adaptations and characteristics

  • Long, slender body, small dermal scales in the skin of some, many vertebrae, long ribs, no limbs, and a terminal anus

  • Eyes are small, most species are blind

  • Special sensory tentacles on the snout

  • Almost entirely burrowing or aquatic

  • Food mostly worms and small invertebrates, which they find underground.

  • Fertilization is internal and males have protrusiblecopulatory organ.

  • Deposit eggs in the ground or near water, some have aquatic larvae larval development occurs within the egg in others.

  • Some exhibit parental care, others vivparity.


Caecilian adaptations and characteristics

video


BC species


Salamanders: Order Urodela (Caudata)

553 species, widespread

9 species in BC

Coeur d’ Alene Salamander,

Plethodonidahoensis


BC Salamanders

Northwestern salamander (Ambystomagracile)

Western long-toed salamander (Ambystomamacrodactylum)*

Tiger salamander (Ambystomatigrinum)*

Coast giant salamander (Dicamptadontenebrosus)

Wandering salamander (Aneidesvagrans)

Coeur d’Alene salamander (Plethodonidahoensis)*

Western redback salamander (Plethodonvehiculum)*

Ensatina (Ensatinaeschscholtzii)

Roughskin newt (Tarichagranulosa)

*Found in Southern Interior


Salamander Adaptations

  • Life Cycles

  • Respiration

  • Paedomorphosis


Salamander Life Cycles

Aquatic or terrestrial throughout entire life cycle, but ancestral condition is metamorphic (aquatic larvae, terrestrial adults)

Eastern Newts are slightly different…

3 life stages

Aquatic – terrestrial – aquatic


Salamander Life Cycles

Eggs fertilized internally


Salamander Respiration

Diverse array of respiratory mechanisms

  • extensive vascular nets in skin for gas exchange

    - may also have lungs, gills, both, or neither

  • Aquatic larvae have gills, but lose them after metamorphosis (but some have fully aquatic life)

  • Some have lungs fully present from birth

    - Some aquatic forms breathe primarily with lungs


Amphiuma respiration

Completely aquatic life history with reduced metamorphosis; lose gills before adulthood, breath through lungs by pointing nostrils above surface of the water to get air


Plethodontid respiration

-All species of Plethodontidae are lungless, many strictly terrestrial

-Cutaneous respiration, supplemented by pumping air through the mouth

-Likely evolved in ancestor that occupied swift streams

Some retain permanently larval, gilled form

*only group of vertebrates to have a form that has neither gills nor lungs at any stage of life history.


Salamander Paedomorphosis

Perennibranchiate mud puppies


Conditional Paedomorphosis

  • Under some conditions, will reach sexual maturity in larval forms, but under other conditions will tranfsorm

  • Ambystoma spp. (like tiger salamanders) include naturally non-transforming types, and others that can be experimentally induced to transform

Tiger salamander adult that has undergone metamorphosis

Axolotl – a neotenic salamander that fails to undergo metamorphosis; adults are gilled


Bolitoglossaplethontid salamanders halt the growth of digits and retain pad-like feet and hands that produce adhesion and suction to attach to vertical surfaces


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