istics, and habitat associations of amphibians have the potential to impact susceptibility to ranaviruses. . relationship with host characteristics and phylogeny. Genomic evidence for cryptic speciation in tree frogs from the Apennine . Phylogeny of map frogs, Boana semilineata species group, with a new .. Scinax ) with description of a novel species-habitat association for an aquatic breeding frog. relation to environmental niche and phylogenetic history. We quantified many frogs works well in a wide variety of habitats. Introduction.
Terrestrial salamanders are usually found on the forest floor under rocks or logs, from which they emerge at night to feed.
Aquatic forms live on the bottoms of streams or ponds, often under stones. Salamanders are usually seasonal in their activity and are easily found only during their active season, which differs among species. Salamanders are unusual among animals in having very large amounts of DNA in their nuclear genomes reviewed by Morescalchi, ; Larson, ; Raff and Kaufman, Genome size measured as C-value mass of DNA in a haploid, unreplicated nucleus ranges from approximately pg.Speciation
Much of this DNA is repetitive and may constitute retrotransposons Marracci et al. Large genomes may limit rates of differentiation during development Sessions and Larson, See Duellman and Trueb for detailed coverage of the biology of salamanders, and Estes for treatment of fossil salamanders.
For reviews of various aspects of salamander reproductive biology and phylogeny, see Bruce et al. Characteristics In addition to presence of a tail and usually two pairs of limbs of approximately equal size, salamanders are distinguished from other amphibians by a combination of several technical features of the skeleton and musculature. These include 1 absence of an otic notch and middle ear, 2 presence of a large footplate and short stylus on the columella in most taxa, 3 absence of postorbital, postparietal, tabular, supratemporal, jugal, quadratojugal present in Karauridaesupraoccipital, basioccipital and ectopterygoid bones, 4 presence of ribs, 5 presence of true teeth on both jaws, 6 gill slits and external gills in aquatic larvae when present7 origin of the adductor mandibulae internus superficialis muscle on the top and back of the skull except Karauridae and small size of the levator mandibulae posterior.
See Duellman and Trueb for further coverage of these characters. Living salamanders are divided taxonomically into ten taxonomic families based upon phylogeny and anatomical features: Ambystomatidae mole salamandersAmphiumidae amphiumasCryptobranchidae hellbendersDicamptodontidae Pacific giant salamandersHynobiidae, Plethodontidae lungless salamandersProteidae mudpuppiesRhyacotritonidae torrent salamandersSalamandridae true salamanders and newts and Sirenidae sirens.
Some extinct species known only from fossils are grouped into the families Batrachosauroididae, Karauridae, Prosirenidae and Scapherpetontidae. Each extant family of salamanders is described in more detail on further pages. These families are grouped into four taxonomic suborders as follows: A few Mesozoic fossil salamanders genera Comonecturoides, Galverpeton and Hylaeobatrachus, each containing a single species have not been assigned to taxonomic families or suborders. See FrostDuellman and Trueb and Duellman for further information on classification of salamanders.
Discussion of Phylogenetic Relationships Monophyly of each of the 10 extant salamander families is well established. Evidence for monophyly of the families is discussed on the separate Tree of Life pages devoted to each family.
The phylogenetic relationships among the different families of salamanders have been somewhat difficult to resolve Larson, ; Larson and Dimmick, ; Larson et al. Larson and Dimmick investigated salamander relationships based on an analysis of phylogenetically informative characters from aligned ribosomal RNA sequences [both large and small subunit], 20 from structures of the head and trunk, and 12 from anatomy of the cloaca.
Gao and Shubin investigated higher-level salamander relationships using combined morphological and molecular nuclear ribosomal RNA from Larson and Dimmick, data, placing three of four families comprised of paedomorphic species in a single clade. In contrast, previous phylogenies e.
Their molecular data consisted of 1, characters: It is thought they may have propelled themselves with their forelimbs, dragging their hindquarters in a similar manner to that used by the elephant seal.
Extensive swamps developed with mossesfernshorsetails and calamites. Air-breathing arthropods evolved and invaded the land where they provided food for the carnivorous amphibians that began to adapt to the terrestrial environment. There were no other tetrapods on the land and the amphibians were at the top of the food chain, occupying the ecological position currently held by the crocodile. Though equipped with limbs and the ability to breathe air, most still had a long tapering body and strong tail.
They still needed to return to water to lay their shell-less eggs, and even most modern amphibians have a fully aquatic larval stage with gills like their fish ancestors. It was the development of the amniotic egg, which prevents the developing embryo from drying out, that enabled the reptiles to reproduce on land and which led to their dominance in the period that followed. According to the fossil record, Lissamphibiawhich includes all modern amphibians and is the only surviving lineage, may have branched off from the extinct groups Temnospondyli and Lepospondyli at some period between the Late Carboniferous and the Early Triassic.
A molecular phylogeny, based on rDNA analysis, suggests that salamanders and caecilians are more closely related to each other than they are to frogs. It also appears that the divergence of the three groups took place in the Paleozoic or early Mesozoic around million years agobefore the breakup of the supercontinent Pangaea and soon after their divergence from the lobe-finned fish. The briefness of this period, and the swiftness with which radiation took place, would help account for the relative scarcity of primitive amphibian fossils.
In the water, the sideways thrusts of their tails had propelled them forward, but on land, quite different mechanisms were required. Their vertebral columns, limbs, limb girdles and musculature needed to be strong enough to raise them off the ground for locomotion and feeding.
Terrestrial adults discarded their lateral line systems and adapted their sensory systems to receive stimuli via the medium of the air. They needed to develop new methods to regulate their body heat to cope with fluctuations in ambient temperature. They developed behaviours suitable for reproduction in a terrestrial environment. Their skins were exposed to harmful ultraviolet rays that had previously been absorbed by the water.
The skin changed to become more protective and prevent excessive water loss. It has an average length of 7. Their metabolic rate is low and as a result, their food and energy requirements are limited. In the adult state, they have tear ducts and movable eyelids, and most species have ears that can detect airborne or ground vibrations.
They have muscular tongues, which in many species can be protruded. Modern amphibians have fully ossified vertebrae with articular processes. Their ribs are usually short and may be fused to the vertebrae.
Their skulls are mostly broad and short, and are often incompletely ossified. Their skin contains little keratin and lacks scales, apart from a few fish-like scales in certain caecilians. The skin contains many mucous glands and in some species, poison glands a type of granular gland. The hearts of amphibians have three chambers, two atria and one ventricle. They have a urinary bladder and nitrogenous waste products are excreted primarily as urea. Most amphibians lay their eggs in water and have aquatic larvae that undergo metamorphosis to become terrestrial adults.
Amphibians breathe by means of a pump action in which air is first drawn into the buccopharyngeal region through the nostrils.
These are then closed and the air is forced into the lungs by contraction of the throat. They usually have long hind limbs that fold underneath them, shorter forelimbs, webbed toes with no claws, no tails, large eyes and glandular moist skin. The difference is not a formal one taxonomically and there are numerous exceptions to this rule.
Members of the family Bufonidae are known as the "true toads".
They are found worldwide except for polar areas. Future molecular studies should provide further insights into their evolutionary relationships. These are AscaphidaeBombinatoridaeDiscoglossidae and Leiopelmatidae which have few derived features and are probably paraphyletic with regard to other frog lineages.
These have certain characteristics that are intermediate between the two other suborders. Ninety-six percent of the over 5, extant species of frog are neobatrachians. This is a symplesiomorphic trait and they are no more closely related to lizards than they are to mammals. They range in size from the Chinese giant salamander Andrias davidianuswhich has been reported to grow to a length of 1. The family Plethodontidae is also found in Central America and South America north of the Amazon basin ;  South America was apparently invaded from Central America by about the start of the Miocene23 million years ago.
They may be terrestrial or aquatic and many spend part of the year in each habitat. When on land, they mostly spend the day hidden under stones or logs or in dense vegetation, emerging in the evening and night to forage for worms, insects and other invertebrates.
A number of fossil cryptobranchids have been found, but there are only three living species, the Chinese giant salamander Andrias davidianusthe Japanese giant salamander Andrias japonicus and the hellbender Cryptobranchus alleganiensis from North America. These large amphibians retain several larval characteristics in their adult state; gills slits are present and the eyes are unlidded.
A unique feature is their ability to feed by suction, depressing either the left side of their lower jaw or the right. As well as breathing with lungs, they respire through the many folds in their thin skin, which has capillaries close to the surface.
They differ from the cryptobranchids by having fused prearticular bones in the lower jaw, and by using internal fertilisation. In salamandrids, the male deposits a bundle of sperm, the spermatophoreand the female picks it up and inserts it into her cloaca where the sperm is stored until the eggs are laid.
The family Salamandridae includes the true salamanders and the name " newt " is given to members of its subfamily Pleurodelinae. Members of this order are eel -like aquatic salamanders with much reduced forelimbs and no hind limbs. Some of their features are primitive while others are derived. Despite this, the eggs are laid singly, a behaviour not conducive for external fertilisation.
These are long, cylindrical, limbless animals with a snake- or worm-like form.
The adults vary in length from 8 to 75 centimetres 3 to 30 inches with the exception of Thomson's caecilian Caecilia thompsoniwhich can reach centimetres 4.
A caecilian's skin has a large number of transverse folds and in some species contains tiny embedded dermal scales. It has rudimentary eyes covered in skin, which are probably limited to discerning differences in light intensity. It also has a pair of short tentacles near the eye that can be extended and which have tactile and olfactory functions. Most caecilians live underground in burrows in damp soil, in rotten wood and under plant debris, but some are aquatic.
Others brood their eggs and the larvae undergo metamorphosis before the eggs hatch. A few species give birth to live young, nourishing them with glandular secretions while they are in the oviduct. Local thickenings often called warts are common, such as those found on toads. The outside of the skin is shed periodically mostly in one piece, in contrast to mammals and birds where it is shed in flakes. Amphibians often eat the sloughed skin. The similarity of these to the scales of bony fish is largely superficial.
Lizards and some frogs have somewhat similar osteoderms forming bony deposits in the dermis, but this is an example of convergent evolution with similar structures having arisen independently in diverse vertebrate lineages.
Granular poison gland, D: Connective tissueE: Stratum corneumF: Dermis Amphibian skin is permeable to water. Gas exchange can take place through the skin cutaneous respiration and this allows adult amphibians to respire without rising to the surface of water and to hibernate at the bottom of ponds. The secretions produced by these help keep the skin moist. In addition, most species of amphibian have granular glands that secrete distasteful or poisonous substances.
Some amphibian toxins can be lethal to humans while others have little effect. These three cell layers consist of the melanophores occupying the deepest layerthe guanophores forming an intermediate layer and containing many granules, producing a blue-green colour and the lipophores yellow, the most superficial layer.
Amphibian - Wikipedia
The colour change displayed by many species is initiated by hormones secreted by the pituitary gland. Unlike bony fish, there is no direct control of the pigment cells by the nervous system, and this results in the colour change taking place more slowly than happens in fish.
A vividly coloured skin usually indicates that the species is toxic and is a warning sign to predators. They all have four limbs except for the legless caecilians and a few species of salamander with reduced or no limbs. The bones are hollow and lightweight.
The musculoskeletal system is strong to enable it to support the head and body. The bones are fully ossified and the vertebrae interlock with each other by means of overlapping processes. The pectoral girdle is supported by muscle, and the well-developed pelvic girdle is attached to the backbone by a pair of sacral ribs. The ilium slopes forward and the body is held closer to the ground than is the case in mammals.
Some salamanders have fewer digits and the amphiumas are eel-like in appearance with tiny, stubby legs. The sirens are aquatic salamanders with stumpy forelimbs and no hind limbs. The caecilians are limbless. They burrow in the manner of earthworms with zones of muscle contractions moving along the body. On the surface of the ground or in water they move by undulating their body from side to side. In the walkers and runners the hind limbs are not so large, and the burrowers mostly have short limbs and broad bodies.
The feet have adaptations for the way of life, with webbing between the toes for swimming, broad adhesive toe pads for climbing, and keratinised tubercles on the hind feet for digging frogs usually dig backwards into the soil.
In most salamanders, the limbs are short and more or less the same length and project at right angles from the body. Locomotion on land is by walking and the tail often swings from side to side or is used as a prop, particularly when climbing.
In their normal gait, only one leg is advanced at a time in the manner adopted by their ancestors, the lobe-finned fish. Adult frogs do not have tails and caecilians have only very short ones.
Certain species in the Plethodontidae have a weak zone at the base of the tail and use this strategy readily. The tail often continues to twitch after separation which may distract the attacker and allow the salamander to escape.