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Chapter 10. Lissamphibia Smooth (Liss-Gr) skin (derived) – Unlike dermal scales of older nonamniotes Earliest fossils of modern forms Permian (vertebrae – salamander and frog likeness) – Earliest complete fossil – Triadobatrachus Stem anuran (frog) – Triassic – Other modern lineages Jurassic fossils Independent evolutionary history for a long time – Salamander form ancestral – frog and caecilian derived Amphibian Characteristics Skin Structure – mucus and poison glands – Moist for gas exchange Carnivorous adults Anamniotic egg (like fishes) Columella (= stapes) modified to transmit sounds to inner ear Green rods in retina (unusual) – Salamanders and frogs (caecilians reduced eyes) Often have two-phase life history – Larvae/adult Salamanders - Urodela Generalized body form – Probably ancestral locomotion 10 families – 515 species – Confined to N. Hemisphere – Peak diversity in N. and Central Am. Paedomorphosis common – retention of juvenile characteristics – Lateral line, no eyelids, external gills Most terrestrial, some aquatic and legless Urodela (cont.) Largest – Andrias (asian) – 1 meter – Largest N.A. - Cryptobranchus – 60cm – Aquatic, members of Cryptobranchidae Lost external gills Other aquatic groups – Proteidae (Necturus) – mudpuppy – Sirenidae (Siren) – front legs only – Amphiumidae (Amphiuma) – lost gills, 4 legs Many forms are cave-dwellers Urodela (cont.) Other families of note – Ambystomidae (mole salamanders) N.A. – large, terrestrial, aquatic larvae Tiger salamanders in MT – Salamandridae (newts) Most European – many aquatic – Plethodontidae (lungless salamanders) Most diverse group Plethodontidae No lungs – most are terrestrial – Cutaneous respiration – Hyobranchial apparatus (used for buccal pumping in species with lungs) used for tongue protrusion – Along with this is forward placement of eyes (depth perception) – Many forms have lost aquatic larvae Eyes on sides, use suction feeding as larvae Plethodontidae (cont.) Social Behavior – Bob Jaeger – Males territorial – mark with pheromones – Nasolabial grooves used to pick up pheromones – Recognize “normal” neighbors Dear enemy phenomenon – New neighbors cause aggressive displays Lower feeding rates Anurans 29 families – 4800 species (worldwide) Body modified for jumping (saltation) – Elongated pelvis (ilium) and fused vertebrae (urostyle) – Eyes forward (depth perception) Locomotor types – – – – Jumpers (e.g. Ranidae – “frogs”) Swimmers (webbed toes, streamlined) Arboreal forms (narrow waist, long legs, toe pads) Hoppers/walkers (“toads”) Toe Pads Peglike projections with canals – Mucus glands – Capillary action and viscosity hold frog on Lifted from back to front – Resting frogs face upward Ecological Correlates Hoppers – wide ranging predators – Potent defensive chemicals Some aposomatic Jumpers – ambush predators – Cryptically colored, flee to avoid predation Feed with tongue (flip out) Most tadpoles herbivorous Some Anuran Families Bufonidae - toads – primarily terrestrial (400 sp) Hylidae – mostly arboreal – small, treefrogs (760 sp) Dendrobatidae – poison arrow frogs (185 sp) – central and south am. Ranidae – typical frogs – many aquatic (700 sp). Gymnophiona - Caecilians Number of families and species ? Aquatic, burrowing – legless Eyes reduced or missing Dermal folds (annuli) and some have dermal scales (unique) Tentacles beside snout (chemosensors) Some brood eggs, some viviparous Amphibian Life Histories Highly diverse Caecilians – most viviparous – Internal fertilization – Offspring eat secretion and cells of oviduct – Oviparous forms brood eggs – Embryos have long gills Amphibian Life Histories (cont.) Salamanders – All except Cryptobranchidae and Sirenidae have internal fertilization – Spermatophores used – Elaborate courtship displays Males use pheromones – Aquatic species – enlarged fins, water currents – Terrestrial species – apply directly (some abrade females with teeth) Amphibian Life Histories (cont.) Salamanders (cont.) – Eggs and larvae Aquatic forms lay eggs in water – gilled larvae Some terrestrial forms lack aquatic larvae – Embryos have gills though 4 species give live birth Amphibian Life Histories (cont.) Anurans – Explosive breeders – short period E.g. toads – often ephemeral habitats – Prolonged breeders – longer Males establish territories – females arrive continuously High variance in male mating success Amphibian Life Histories (cont.) Anuran Vocalizations – Attract females, frequency inversely correlated with body size – Costs Energetic – can be more than locomotor Predation – tungara frogs – whine/chuck – Predators (bats) home in Amphibian Life Histories (cont.) Anuran Reproduction – Most external fertilization Amplexus (axillary or inguinal) – Many small eggs – left to hatch – Few large eggs – parental care Foam nests, guarding, carrying offspring Provisioning offspring – Mouth brooders, back brooders, gastric brooders Tadpole Ecology Most tadpoles are herbivorous filter feeders – Strain material in gills Some become carnivorous (e.g. spadefoots) Use different resources than adults Completely metamorphose into adults – Short, vulnerable period – Stimulated by thyroxine Amphibian Gas and Water Exchange Thin, glandular skin for gas exchange and cooling – Circulatory system has 6th arch as “pulmocutaneous artery” Shunt blood to lungs or skin – 2 atria – 1 ventricle Pulmonary and systemic circuits Ventricle avoids mixing of blood Water absorbed by skin – stored in bladder (20-30%) Poison glands Proteins and alkaloids – many with pharmacological uses Often associated with aposomatic coloration – Some have ribs that pierce sides and stab predators Mimicry often present Amphibian Declines In 1989 herpetologists realized that amphibians were in trouble – Declining all over world – cause still unknown Habitat destruction, introduced species Acid precipitation Increased UV Pathogens (viruses and chytrid fungus) – spread more easily by humans (scientists?)