Question

For each of the three amphibian groups Caudata, Anura and Gymnophiona

generally summarize how they reproduce (calling? internal? external? eggs? metamorphosis? direct development etc., any parental care?).

Answer 1

Gymnophiona

Caecilians with long Body slender, wormlike .They are burrowers, found in tropical forests of S. America., Africa, South East Asia

Reproduction:

• Fertilization internal, eggs deposited in moist soil near water
• Some species guard eggs (body folds)
• May or may not have aquatic larval stage
• Complete larval development may occur in egg
• Viviparity common in more advanced forms
• Embryos eat oviduct wall

Caudata

Include Salamanders and newts . Found in almost all tropical and northern temperate regions of world. Most species in North America

Reproduction

• Little diversity of breeding habits
• Eggs of most salamanders fertilized internally
• Female picks up packet of sperm (spermatophore) previously deposited by male onto some substrate
• Ritualistic behaviors help ensure female receptivity
• Additional behaviors ensure recovery of sperm mass by female
• Aquatic species lay eggs in clusters or stringy masses in water
• Often attached to submerged objects
• Terrestrial species lay eggs in tiny, grape- like clusters under logs, in vegetation, or in excavations in soft earth

Development - Some species remain (female) and guard eggs until hatching

• Larvae which hatch are not tadpole-like, Resemble parents
• Still must undergo metamorphosis to attain adult form
• Gills generally lost and fin-like tail modified during metamorphosis
• Size and type of gills dependent on larval habitat
• Larger in lake, pond, smaller in stream habitat
• Lungs usually replace gills in adults (except in aquatic forms)
•   no lungs,Only adult vertebrates with neither lungs nor gills
• Skin highly vascularized - vascular net
• Extension of capillaries into epidermis OR thinning of epidermis over dermal capillaries

Metamorphosis- Most salamanders undergo metamorphosis, but some retain gills or other larval characteristics after becoming sexually mature ,

• Neoteny (young, to extend)
• Some retain characters for entire lifetime - permanent larvae
• Obligatory neoteny
• Either developing tissues fail to respond to thyroxin (metamorphosis hormone) OR pituitary gland doesn’t develop fully to produce thyrotropin that stimulates thyroid gland to produce thyroxin
• Others retain characteristics, but can change if conditions are favorable
• Facultative neoteny - Achieved by delaying somatic development, but not sexual maturation
• Example of facultative neoteny: Ambystoma species - Tiger salamander subspecies called American axolotl -Mexico and SW US
• Remains aquatic, gill- breathing, fully reproductive larval form unless water begins to dry up ,Metamorphoses to adult, loses gills, develops lungs, assumes appearance of ordinary salamander
• Can be artificially induced to metamorphose by treating then with thyroxin
• Essential for normal metamorphosis in all amphibians

Anura

Include Frogs & toads ,Most familiar, successful amphibians

Reproduction

• Most larger frogs are solitary except during breeding season
• Males call noisily for females
• Breeding is first desire after coming out of hibernation
• Males migrate to water first - olfactory cues
• Croak, call to attract females
• Females enter water when eggs mature and are clasped by males - amplexus
• Females lay eggs and males fertilize them
• Eggs laid in large masses, anchored to vegetation
• Jelly layer absorbs water and swells after fertilization
• Development occurs quickly
• Tadpole hatches from protective jelly coat within 6-9 days (temperature- dependent)
• Head and body, tail, ventral mouth with horny jaws, ventral adhesive disc, gills, etc.
• Length of tadpole stage is species- dependent
• Leopard frog completes metamorphosis within 3 months
• Bullfrog takes 2-3 years to complete process