Amphibians I BIOL 4270

Amphibian Diversity & Adaptations Goals: 1)Examine the adaptations that have made amphibians so successful 2)Examine some of the diversity in life histories 3)Examine the characteristics of amphibians that have led to their current distributions 4)Discover some of BC’s amphibians 5)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 1)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, Aneides vagrans Coastal tailed frog, Ascaphus truei Dermophis mexicanus

Characteristics of Modern Amphibians 3) Usually quadrupedal in 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 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, conus arteriosus; 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 Rana temporaria

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

Rough-skinned Newt (Taricha granulosa) 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, Ambystoma tigrinum

Characteristics of Modern Amphibians 7) Ectothermic, body temperature dependent upon environmental temperature and not modulated by metabolically generated heat Great basin spadefoot toad, Spea intermontana

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 FrogCoastal 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 protrusible copulatory 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, Plethodon idahoensis

BC Salamanders Northwestern salamander (Ambystoma gracile) Western long-toed salamander (Ambystoma macrodactylum)* Tiger salamander (Ambystoma tigrinum)* Coast giant salamander (Dicamptadon tenebrosus) Wandering salamander (Aneides vagrans) Coeur d’Alene salamander (Plethodon idahoensis)* Western redback salamander (Plethodon vehiculum)* Ensatina (Ensatina eschscholtzii) Roughskin newt (Taricha granulosa) *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 Axolotl – a neotenic salamander that fails to undergo metamorphosis; adults are gilled Tiger salamander adult that has undergone metamorphosis

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