Vertebrate Zoology Chapter 11 Amphibians PDF

Chapter 11 Amphibians  “Alpha taxonomy” is still in an active discovery phase: since 1985 the number of species recognized...

Chapter 11 Amphibians  “Alpha taxonomy” is still in an active discovery phase: since 1985 the number of species recognized has increased by 60%!! November 14, 2018 - 7,948 February 2, 2021 – 8,275 extant species 7,301 toads and frogs 760 newts and salamanders 214 caecilians Global distribution except for the most isolated oceanic islands Species diversity highest in Subclass: LISSAMPHIBIA tropical regions Anurans (frogs), Urodelans (salamanders), & He Spent His Career Studying a Frog. Then He Gymnophionans (caecilians) Discovered Its True Identity. | Short Film Showcase - YouTube  Amphibian Synapomorphies Short, straight ribs Highly specialized integument, thick dermis with highest gland concentration and diversity of any group of tetrapods Skin often highly vascularized for gas exchange (cutaneous respiration) Dentition pedicellate (teeth set on stalks) Eyes lifted by levator bulbi muscles Many details of ear structure (salamanders, frogs) Adults are carnivores Green rod cells in their eyes  ~ 760 species in 10 families Order URODELA – New species are still being Salamanders & Newts discovered in American tropics & southern Appalachia Species diversity is highest in North America More salamanders in Tennessee than in Europe and Asia combined Distribution is Holarctic, but “recent” entry into South America via Panamanian land bridge Paedomorphosis is widespread in salamanders Salamanders Smallest species: Thorius pennatulus Minute, or pygmy, salamanders Mexico: 3 cm total length Largest species: Andrias davidianus Chinese Giant Salamander China: 1.5 m total length Largest in US: Cryptobranchus alleganiensis Hellbender 60 cm  Lungs completely lost in all species (rely solely on cutaneous & buccopharyngeal respiration) Nasolabial grooves (transfer chemical cues to nostrils from substrate) Hyobranchial apparatus modified for tongue projection (in highly derived taxa) Happy #SalamanderSaturday! - Family Plethodontidae (>50% of YouTube all extant salamander species)  Order ANURA – Frogs & Toads Diversity ~ 7,301 species, 50 families, new species still being discovered Distribution – everywhere but highest altitudes, hottest deserts, & Antarctica Size is variable Largest = “goliath frog” of West Africa 30 cm snout-vent length, up to 1 m with outstretched legs Up to 4+ kg, eats animals as large as rats & ducklings Smallest = “leaf climber” frog from Cuba (genus Eleutherodactylus) – can hide under a dime  More Frogs and Toads The most obvious morphological feature is that frogs & toads are almost universally modified for jumping (saltation) Most of the synapomorphies are in some way associated with this function Elongated hindlimbs, and tibia and fibula are fused Powerful pelvis and stiffened vertebral column Urostyle and pelvis make the back half of the trunk rigid Short vertebral column with little lateral movement Forelimbs absorb impact of landing Large eyes forward on the head, providing binocular vision Possess nictitating membrane to protect eyes How Frogs Got Their Vertical Leap | ScienceTake - YouTube  Types of Frogs Frogs have long legs and move by jumping Usually ambush predators Avoid their own predators with quick, evasive hops Semiaquatic frogs are streamlined and have webbed feet Use suction to engulf food in water  More Frog Types Toads usually have blunt heads, heavy bodies, and relatively short legs, and little webbing in their toes Usually, wide-ranging predators Conspicuous to their own predators, so they usually have potent defensive chemicals that they release from their skin when attacked Arboreal frogs have large heads and eyes and slim waists with long legs Have toe pads with a layer of polygonal plates separated by deep channels Mucus glands secrete polymers that allow them to stick to smooth surfaces by wet adhesion  Adult frogs are all carnivorous, and feed on arthropods, worms, Terrestrial snails, and sometimes small Anurans vertebrates (mice, birds, lizards, other frogs, etc.) Project Their All snap at prey with a slightly protrusible tongue, that is Tongue to attached at the front and free in Capture Prey the back The free end is glandular and produces an adhesive compound that sticks to prey Reversible saliva makes frog tongues sticky - YouTube  Anuran Skin Thin & moist, loosely attached to the body at some points Stratified epidermis with soft keratin, which provides limited protection; epidermal layer is shed periodically (animal usually eats the shed) Thicker dermis characterized by a very high gland concentration and diversity Glands of 2 general types: mucous (water- proofing function) and serous (secrete toxins, usually as whitish, watery fluids) Toxins in skins of some of the species of ‘poison dart frogs’ (Dendrobatidae and Mantellidae), are among the most lethal animal secretions known  Diversity ~ 214 species in 10 families Order Gymnophiona - ~3% of known species of Lissamphibia Caecilians Poorly known From < 20 cm to > 1 m in size Distribution – “pan-tropical” But absent from Australia & Madagascar Eyes reduced & covered with skin or bone Left lung vestigial (reduced, non-functional) Skull extensively reinforced (for burrowing) All have internal fertilization Folds (annuli) in their skin that mark locations of the ribs Protrusible tentacles  Most lay eggs Become larvae or miniatures Amphibian Reproduction of adults Some carry the eggs on their back or in pockets on their bodies Some females keep the eggs in the oviduct and give birth to live young Some provide parental care Transport tadpoles from the nest to water Some stay with the tadpoles Some feed their tadpoles Salamander Reproduction Fertilization is internal in most, but accomplished via interesting courtship rituals Unique structures associated with reproduction: Hedonic glands – gland(s) of “seduction”; usually on chin of ♂ Spermatophore* – sperm packet deposited by ♂ on substrate Spermatheca – sperm “pocket” in dorsal wall of ♀ cloaca Can store viable sperm for a period of 12 days – 1 yr Salamander Courtship Most male salamanders secrete pheromones from their hedonic glands Apply them to the nostrils or body of the female Many species of newts perform elaborate courtship displays These species generally have extreme sexual dimorphism https://www.youtube.com/watch ?v=VEadfTqtkSg https://www.youtube.com/watch ?v=vVqqdgrsJDk  Salamander Offspring Most that breed in water lay their eggs in the water Eggs are single or in a mass of transparent gelatinous material In some species, there is female parental care A few species are viviparous The European alpine salamander (Salmandra atra) gives birth to 1-2 fully developed young (who then consume the unfertilized eggs), about 1/3 of the adult body length Gestation is 2-4 years  Axolotls (Ambystoma mexicanum) are amphibians belonging to the Paedomorphosis in single living genus of the family Ambystomatidae Salamanders More than 30 salamander species in the Ambystoma genus, known as the mole salamanders Wild axolotls live exclusively in the swampy remnants of Lake Xochimilco and the canals leading to it on the southern edge of Mexico City Carnivores - Mollusks, fish and arthropods like insects and spiders Mating “dance” Male and female nudge and stroke one another's cloaca Step in a circle in a sort of waltz The male then struts away while shimmying his tail like a hula dancer, luring the female to follow As the two dance partners step together, the male drops a small white capsule full of sperm called a spermatophore, and the female picks it up with her cloaca Axolotls exhibit neoteny, meaning that they reach sexual maturity without undergoing metamorphosis https://www.youtube.com/watch?v=Eo50ctoOTWs Anuran Reproduction Explosive Breeders - Breeding season is very short Toads and other anurans that breed in temporary aquatic habitats All males and females arrive to the breeding location simultaneously Breeding is equal for all males and females Prolonged Breeders - Breeding season may last for several months Males arrive first, and females arrive gradually, a few at a time Males vocalize to attract females, may indicate the quality of the male Females leave after mating Mating success for males is skewed  Male advertisement call – usually a simple note, purpose is to attract females, proclaim “ownership” of Frog Calls a territory 2 components to most calls – advertisement call and then an added more complex part (quality indicator for females) Chorus formation/cacophony – group calling increases volume & carries sound farther Females choose partners Nostrils must be closed to channel air through vocal sacs as sound is being made Both sexes have vocal cords, but these are usually better developed in males Vocal sacs = resonators that amplify volume Contraction of vocal sacs pushes air back into lungs https://www.youtube.com/watch?v=MubdT4yMat0  Frog Calls (cont’d) Costly in terms of energy and attracting predators Male túngara frogs use whines and chucks Only whine when alone in a pond Use chucks when other males are around https://youtu.be/RMJedhmhUnY Anuran Reproduction External fertilization may have extended amplexus until female lays eggs Internal fertilization may be widespread if frog lays eggs on land and for viviparous species Arboreal frogs lay eggs on leaves overhanging water, tadpoles drop into water; tungara frogs construct floating foam nest Many tropical frogs lay eggs near water and wait for rain to release tadpoles Direct development involves large eggs that develop directly into little frogs Parental Care in Frogs (A) and (B) - Male Bornean guardian frog guarding his eggs, then transporting tadpoles to a stream (C) Both parents care for the eggs and tadpoles of strawberry poison frogs. The male guards the clutch, and when the eggs hatch the female transports tadpoles and deposits them one at a time in water-filled leaf axils of plants. She returns to each tadpole several times during the 6- to 8-week period of development to deposit trophic eggs for the tadpoles, which are obligate egg-eaters (D) Females of some species of treefrogs carry the eggs on their backs, either adhering the surface of the skin or within a pouch of skin (E) The male Darwin’s frog picks up the eggs as the female deposits them and transfers them to his vocal sacs, where the eggs develop through metamorphosis (F) A female Surinam toad carries eggs on her back The https://www.youtube.com/watch?v eggs of this species complete development and hatch as =SgROaJY6Xnk tiny frogs, whereas other species hatch as tadpoles (G) Male African bullfrogs guard the eggs, and then accompany the tadpoles, eventually digging a channel to allow the tadpoles to reach deeper water General Anuran Life-History Strategy Generalized tadpole features: Long tail with a complete fin Both internal & external gills No legs (initially) Mouth-parts specialized for herbivory (salamander larvae are carnivorous) Highly specialized internal anatomy Striking metamorphosis from tadpole to adult No cases of paedomorphosis in anurans Metamorphosis of a Tadpole Frequently distinguished by a 2-stage life cycle, consisting of a free-swimming fully aquatic larval tadpole (or polliwog) stage, followed by metamorphosis into a completely different looking terrestrial adult Changes are stimulated by increased thyroxine; controlled by TSH Anuran Life-History Strategy Eat different things and live in different habitats New Mexico spade foot toads can become carnivores Breeding takes place in temporary pools left by the rain Eggs laid in large masses, often hatch in as little as 48 hours. The tadpoles are forced to metamorphose quickly, before the water dries up Spea multiplicata tadpoles exhibit phenotypic plasticity. Tadpoles that ingest fairy shrimp, when present, may express a novel carnivore phenotype This novel phenotype increases the rate of development, helping the tadpoles to escape drying ponds more rapidly  Internal fertilization Male intromittent organ that Caecilian protrudes from the cloaca Reproduction About 75% of species are viviparous and matrotrophic In some species, after the yolk supply has been used up, they emerge from the egg membranes and stay in the female’s oviducts Scrape fatty cells in a thick, white, creamy substance (uterine milk) from the walls of the oviducts Dermatophagy is a feeding method for some species https://www.youtube.com/watch?v=DMvL4zOLSeM  All amphibians depend on Respiration cutaneous respiration for most of their gas exchange Cutaneous respiration has some disadvantages compared to lung respiration: – Skin must be kept moist in salamanders, a condition too “delicate” for a fully terrestrial life – Gas exchange across skin is constant, it cannot be increased with an increase in activity Anurans are more heavily dependent on lung respiration than are salamanders  While completely submerged a frog's respiration takes place through the skin only The skin is composed of thin membranous tissue that is very permeable to Respiration water and contains a large network of blood vessels When the frog is out of the water, mucus glands in the skin keep the frog moist, which helps absorb dissolved oxygen from the air A frog may also take air in through their nostrils and down into their lungs To draw air into its mouth the frog lowers the floor of its mouth, which causes the throat to expand Then the nostrils open allowing air to enter the enlarged mouth The nostrils then close and the air in the mouth is forced into the lungs by contraction of the floor of the mouth To eliminate the carbon dioxide in the lungs the floor of the mouth moves down, drawing the air out of the lungs and into the mouth The nostrils are opened, and the floor of the mouth moved up pushing the air out of the nostrils Frogs also have a respiratory surface on the lining of their mouth on which gas exchange takes place readily Dominant form of breathing while at rest The lungs, which only adults have, are poorly developed Blood Flow with Lung Respiration Atrium of the heart is divided into left and right chambers by a septum Ventricle is not divided Deoxygenated blood enters the right atrium, then to the dorsal part of the ventricle, then leaves through the pulmocutaneous arch to the lungs Oxygenated blood from the lungs flows into the left side, and deoxygenated blood flows into the right side Oxygenated blood returning to the heart from the pulmonary veins enters the left side of the atrium, then to the left side of the ventricle Carotid and systemic aortic arches branch off from this side, so oxygenated blood flows out to the tissues Blood Flow with Cutaneous Respiration When a frog is breathing through its skin, most of the oxygen is coming from the systemic veins that drain the skin Most of the oxygen does not go through the heart Any oxygen that does, goes into the right atrium and floods the undivided ventricle Blood is then pushed out into the tissues of the head and body  How Do Frogs Survive in Dry Conditions? Many stay underground for 9-10 months each year and only come out when it rains Feed, grow, and reproduce in only a few weeks Some bury themselves in cocoons of their own skin layers that is impermeable to water Many arboreal frogs have skin that is less permeable to water, so they lose less of it Behavioral modifications Only active at night Less active on dry night (postural control) Water Intake Amphibians do not drink water Aquatic amphibians face osmotic influx of water controlled through urine production Terrestrial amphibians have a pelvic patch that absorbs water quickly Aquaporins are tubular proteins in the plasma membranes of cells in this area that act as channels for water absorption  Mucus, Toxins, and Venom Some species have mucus that makes them slippery and hard for predators to grab Others have mucus that makes them sticky Some salamanders have sticky mucus glands on their tails, and they hit predators with it so that debris sticks to them Other salamanders will secrete sticky mucus that makes snakes get stuck in a coil  Mucus, Toxins, and Venom Many amphibians secrete toxins from their granular glands (see previous slide for these glands) Usually on the dorsal surface, and both frogs and salamanders present the glands to potential predators Often get their toxins from foods Dendrobatidae (poison dart frogs) get theirs from ants, beetles, and millipedes that they eat Strawberry poison dart frog females feed their tadpoles trophic eggs that contain alkaloids Most have aposematic coloration Mucus, Toxins, and Venom Some salamanders have ribs that extend through the body wall and carry toxins from the granular glands If a predator bites them, they get poked and toxins are released, making some amphibians venomous Some frogs have bony spines on their skulls that have concentrations of granular glands Some caecilians are venomous Skin covers bony spikes  Teaching/Research: biphasic life cycle (tadpole ecology, community ecology), acoustic communication, ecosystem structure/function Toxicology: exposure to poisons, pesticides, etc., at land/water interface; used extensively to assess ecosystem health (“canary Important Roles of in the coal mine”) Amphibians to Medicine: basic research on hormones of Human Welfare thyroid/pituitary glands, frog skin toxins as pain- killers, limb regeneration in salamanders  More than 40% of amphibian species are classified as at some level of risk Declining Amphibian Diseases from invasive species Diversity Ranaviruses are double stranded DNA viruses that can cause severe infections in amphibians, reptiles, and fish First noted in the late 1980s Mortality rate of 90%-100% Outbreaks can affect multiple species at the same time and are often associated with acute die- offs and population declines of wild amphibians Declining Amphibian Diversity Chytridiomycosis Caused by the fungus Batrachochytrium dendrobatidis (Bd) Has caused the decline or complete extinction of over 200 species of frogs and other amphibians. Chytrid disease is known to affect over 350 species of amphibians, though it appears to be impacting frog species most severely Does not infect all frog species Bd infects the keratin layer of the skin, where it multiplies by producing zoospores, which are shed into the environment The zoospores can live for weeks in water depending on the temperature Batrachochytrium salamandrivorans (Bsal) recently discovered in fire salamanders in the Netherlands 90% population reduction in 6 months, completely extinct in 2 years https://theconversation.com/a-skin-eating-fungus-from-europe-could- decimate-appalachias-salamanders-but-researchers-are-workingto- prevent-an-outbreak-149418