Amphibians PDF

Amphibians These foul and loathsome animals are abhorrent because of their cold body, pale color, cartilaginous skeleton, filthy skin, fierce aspect, calculating eye, offensive smell, harsh voice, squalid habitation, and terrible venom; and so their Creator has not exerted his powers to make many...

Amphibians These foul and loathsome animals are abhorrent because of their cold body, pale color, cartilaginous skeleton, filthy skin, fierce aspect, calculating eye, offensive smell, harsh voice, squalid habitation, and terrible venom; and so their Creator has not exerted his powers to make many of them. Carl von Linne (Linnaeus) Systema Naturae (1758) Amphibians Long hind limbs  Lissamphibia – smooth Short, stiff bodies skin + double life Equal-sized  First vertebrates adapted limbs to land Long, slender bodies  After plants, insects, snails No limbs salamander  Not completely land Long, slender bodies adapted  Cannot be far from water?  Structurally between fish and reptiles  Food is protein-rich – do not store great quantities of fat or glycogen  Ectotherms, low metabolic rate – low food demand Amphibians – movement to land  1) O2 content of air greater than water (less effort to take up O2 from air)  2) air less dense (lack of body support)  3) greater temperature fluctuations (unpredictable temperature extremes)  4) greater habitat variety (cover, shelter, breeding areas)  Gills vs lungs? Advantages vs Shared characteristics  1) Smooth moist skin  Absence of bony or keratinized scales (except caecilians) Cool, wet nights Warm, dry nights  Absence of claws  Mucous glands or granular glands Prevent desiccation, predation, and can shed diseases Ways to prevent water loss? Behavioral modifications Pelvic patch Permeable bladder Skin  1.1 Poison glands  Concentrated on dorsal surface (top)  Diverse array of chemicals  Most sequestered from diet  Associated with mucous glands?  Tarichatoxin (newts) Water-soluble alkaloid, blocks NA+ channels  Epibatidine (frogs) Lipid soluble alkaloid, blocks Ach receptors, non-addictive painkiller  Batrachotoxin (frogs) Lipid soluble alkaloid, blocks closing of NA+ channels, sequestered via diet  2 - Multiple methods of  3 – Teeth respiration  Not present in all, but if they are special type  Cutaneous breathing thru skin  Pedicellate – crown and base of tooth  Buccopharyngeal cheek breathing separated by uncalcified dentine or  Pulmonary lungs fibrous tissue  Allows for “flex”  Gills  4 – Eye structures  Most dominant sense, if present.  Lachrymal glands and eyelids bulgelevator  Green rods present  Levator bulbi muscle  5 – Reduction in skull bones  6 – Biphasic lifestyle  7 – Hearing  Operculum – columella complex Two bones in middle ear that transmit sound to inner ear Also hear low frequencies via scapula Lungs & Circulation  Improved on efficiency of simple lung  Supplied it with capillary network to improve O2 uptake  Double circulation  Systemic – blood to body  Pulmonary – blood to lungs lungs  Frogs and toads are the best amphibians at lung breathing  Amphibians may employ cutaneous respiration  Several disadvantages of cutaneous respiration  Skin must be kept thin and moist  Gas exchange rate is nearly constant lungs  Positive-pressure breathers  All higher vertebrates use negative-pressure system feeding  Snap at prey with protrusible tongue  Attach at front, free behind, 99% of the time  Free end very glandular, produces sticky secretion, adheres to prey Order Gymnophiona  Caecilians - Body long, slender, wormlike, limbs absent. “vermiform”  Many vertebrae, long ribs, and tail absent  Small, mostly degenerate eyes (mostly blind as adults)  Sensory tentacles on snout  Burrowers, tropical forests of S. Amer., Africa, SE Asia  Feed on worms, small invertebrates  Fertilization internal, eggs deposited in moist soil near water Order Caudata – tailed ones  Salamanders and newts  Least specialized amphibians  Diversity associate w/ cool, wet forests  Most species in N. America Japanese giant salamander  Well developed limbs, 2 pairs equal, right angles, can regenerate lost limbs via blastema, medical research?  Most have internal fertilization (most)  Lack tympanum and middle ear Order Caudata  Some species have rudimentary limbs  Why? Lost thru time visual trait Order Caudata -  Paedomorphosis widespread  Adults retain laterally compressed tail, flattened head, lateral line system, external gills (not always)  Prey capture  Mouth gape to pull prey in via suction in water  Terrestrial – thick sticky tongue. No lungs led to hyoid bone  Nasolabial grooves –  Aids in collection of chemicals, again no lungs. Order Caudata -  Respiration primarily gills but can vary to cutaneous  Cryptobrachidae – lungs 50%/ skin 50%  Plethodontidae – skin 10% / buccopharynx 90%. No lungs?! Why? Order Caudata - Hellbender  Aka snot otters, lasagna lizard, devil dog  IUCN redlisted and FWS protection Order Caudata - Newts  All rough skinned  Unken reflex  Aposematic – coloration  Tarichatoxin – very poisonous, can lead to paralysis Order Caudata - reproduction  Eggs of most salamanders fertilized internally  No direct copulation  Female picks up packet of sperm (spermatophore) previously deposited by male onto some substrate Order Caudata - development  Larvae which hatch are not tadpole-like  Resemble parents  Still must undergo metamorphosis to attain adult form Order Caudata - development  Size and type of gills dependent on larval habitat  Larger in lake, pond, smaller in stream habitat  Some keep gills into adult stages  Neoteny – retaining larval characteristics into adulthood  Facultative vs obligative neoteny Order Caudata - no lungs  Some salamanders don’t bother developing lungs when they lose gills  Family Plethodontidae - lungless salamanders - most of familiar N. Amer. Salamanders  Only adult vertebrates with neither lungs nor gills!  If they had lungs – they would provide to much buoyancy and float away! Order Anura  Frogs & toads, >3400 species  Obvious, common characteristic - lack of tail in adult  All pass through tailed larval stage  Specialized legs for jumping  Skull much lighter than in fishes  Toads poses parotid gland Order Anura  No visible neck  Caudal vertebrae fused (to form urostyle)  Ribs generally absent  Why?  Hindlegs much enlarged Order Anura  Mating systems  Explosive breeders – temporary aquatic habitats, large aggregations, limited mate choice  Prolonged breeders – males defend territories, males out-number females; strong mate choice  Amplexis can range from hours to days Order Anura  Tadpole  Long, finned tail  Both internal, external gills  No legs  Specialized mouthparts for herbivory (salamander larvae are carnivorous)  Highly specialized internal anatomy  Neoteny never exhibited in frogs or toads Order Anura  21 different families  Common North American frogs  Ranidae - grass frogs  Hylidae - tree frogs  Bufonidae - true toads Cane toad and bullfrog  One of the top 10 worst invasive species worldwide. (cane toad)  Prolific breeders (all year)  Tolerance for temperature / salinity  Life stages  Diet  100 released in 1935 Green frog Here, we use sex-linked molecular markers to discover sex reversal in wild populations of green frogs (Rana clamitans) inhabiting ponds in either undeveloped, forested landscapes or in suburban neighborhoods. Our work here begins to suggest that sex reversal may be common within and across green frog populations, occurring in 12 of 16 populations and with frequencies of 2–16% of individuals sampled within populations. Additionally, our results also suggest that intersex phenotypic males and sex reversal are not correlated with each other and are also not correlated with suburban land use. While sex reversal and intersex are often considered aberrant responses to human activities and associated pollution, we found no such associations here. Our data perhaps begin to suggest that, relative to what is often suggested, sex reversal may be a relatively natural process in amphibians. Wood frog freezing