Download Chapter 10. Lissamphibia Amphibian Characteristics Salamanders

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?)