AmphibiansAmphibiansare transitional in different ways between the plenary aquatic and fishesamniotes. But, they are not simply transitional in their morphology, lifehistory, ecology, and comportment. In the prosperous procurement ofindependence from water and colonization of land, amphibians have undergone aremarkable adaptive radiation, and the living groups reveal a countlessdiversity of modes of life history than any other group of vertebrates (Duellman,1994). Figure 1: Amphibians Theirshell-less eggs have been studies extensively by developmental biologists, andmuch of the basic understanding of vertebrate embryology is predicated onamphibians. The metamorphosis from aquatic larvae to terrestrial adults hasbeen the subject of intensive studies, and much of what is kenned about theaction of thyroid and pituitary hormones has originated from endocrinologystudies on amphibians. Likewise, the facileness of breeding amphibians in thelaboratory and their relatively simple chromosomes complements have providedbases for consequential advances in studies of hybridization andspecialization. The vocalizations of frogs have provided an expedient forstudying acoustic communication and, together with other aspects of courtshipand mating, have presented and evolutionary biologist with a wealth of materialfor studies on sexual cull. These are a few culled examples of the exhilaratingways in which studies of amphibians are contributing to erudition of biologyand out understanding of biological phenomena (Duellman, 1994).
Theterm amphibian can be interpreted in two ways-either as an animal spending partof its life in water and then transmuting to an aquatic adult, or as an animalthat alternates life in and out of water, such as pond frogs.Accordingto Duellman, W. (1994), amphibians can be defining as quadrupedal vertebrates havingtwo occipital condyles on the skull and no more than one sacral vertebra. Theskin is glandular and lacks the epidermal structures (scales, feathers, hair) featuresof other groups of tetrapod’s. Yet, some Paleozoic amphibians were large,plated quadrupeds, most living amphibians are small. The most astronomicallyimmense salamander procures a total length of about 1500mm, whereas the mostimmensely colossal frog is about 300mm. caecilians reach a length of about1500mm. Caecilians and some salamanders lack limbs and girdles, and in someother salamanders these structures are reduced.
In frogs the post sacralvertebrae are fused into a single rod like element, the coccyx, the tail isabsent, and the hind limbs are elongated and modified for jumping. Albeitepidermal scales are absent in amphibians, dermal scales are present in theskin of most caecilians. A highly glandular skin contains both mucous andgranular glands.
True claws are absent, but horny tips are present on the toesof some frogs and salamanders.Within,the structure of living amphibians is intermediate between that of fishes andamniotes. The heart has to atria, a single ventricle, and a distinct conusarteriosus with numerous valves. The aortic arches are proportioned. Usually,amphibians have two lungs, but the lungs are reduced in some salamanders andabsent in one entire family.
The left lung is greatly reduced in most of theelongate caecilians. Living amphibians also have some distinctive characters.They all have pedicellate teeth and specialized papillae in the inner ear, andsalamanders and anurans have green rods in the retina of the eye.Thelife histories of amphibians are highly diversified. Most species of frogs haveexternal fertilization, where internal fertilization occurs in the bulk ofsalamanders and probably in all caecilians.
The classic amphibian life historyof aquatic eggs and larvae, where typically of many frogs and some salamanders,is only one of the many modes of reproduction, which consist of directdevelopment of terrestrial eggs, ovoviviparity, and even viviparity. Allamphibian eggs must develop in moist situations, for although they have severalprotective mucoid capsules, these capsules are highly permeable. The eggs lacka shell and the embryonic membranes of higher vertebrates. In those amphibiansthat have aquatic larvae, the larvae undergo metamorphosis into the adult form;this is an especially dramatic change in frogs (Duellman, 1994). a. AmphibianNamesPeopleused three variants of names when verbalizing about amphibians, and alldescribe the animal to one degree or another. Colloquial designations are namesutilized by people within categorical areas of the country for an individualspecies or group of amphibians, but these have little or no apperception beyondthe area or immediate use. In the South, the terms “spring lizard,” forexample, is often used to refer to salamanders that are utilized as allurement,regardless of the species involved, or whether “the lizard” is not a reptile atall, but an amphibian.
Other colloquial names include waterdog, puppy canine,hop toad, and tree toad. In herpetology, reptiles customarily receive the morecolorful colloquial denominations (Dodd, 2004). Figure 2: Spring Lizard Prevalentdenominations are utilized by the general public and biologists kindred toidentify species.
Some common names are often used incorrectly, sometimes todifferentiate frogs from toads or salamanders from nets. Prevalent names oftenare descriptive of the animal, such as “Spotted Salamander” for the salamanderAmbystoma maculatum. This species has harge, bright orange, yellow or red spotson its dark back, thus making the common name very opportune. Sometimescolloquial designations, such as mudpuppy, can even become accepted commondesignations. Figure 3: SpottedSalamander in Orange Spot Figure 4: SpottedSalamander in Yellow Spot Moreover,Dodd, K. (2004), explained the terms Urodela and Apoda are sometimes used insteadof Caudata and Gymnophiona for salamanders and caecilians. However, in someliterature Salientia is utilized interchangeably with Anura for frogs.
Even commonEnglish names become obscure. It is not (‘unusual’, ‘eccentric’, ‘unorthodox’,’unwonted’) in the literature to find “salamanders and newts” or “frogs andtoads.” Newts are aquatic members of the family Salamandridae, and aresalamanders. Similarly, at least in the narrow sense, toads are members of thefamily Bufonidae, and are frogs in the broad sense. Thus, all newts aresalamanders, but not all salamanders are newts, and all toads are frogs, but notall frogs are toads. To avoid misperception, the terms new and toad areutilized in their narrow sense; in referring to all frogs and toads, theordinal derivative anuran is utilized.
b. AmphibianRichness and BiogeographyAccordingto Dodd, K. (2004), throughout the world, there are approximately 4,700 speciesof amphibians currently describe: more than 440 are salamanders, 165 arecaecilians, and the rest are frogs. More than 240 amphibian species are foundin North America. The greatest number of amphibian species occurs in thetropics, particularly among the frogs of South America, Australia, South Asia,and Africa, including Madagascar. There are no frog families that have theircenters of species richness within the southern mountains, and only a fewgenera even have their greatest diversity within the southeastern UnitesStates. In many respects, frogs seem tobe peripheral lowland invaders of the high Appalachians.
The region oftemperate North America with the greatest species richness of frogs is theSouth Atlantic Coastal Plain.Thevery large salamander family Plethodontidae, on the other hand, has two centersof species richness, one of which is in the Southern Appalachian region; theother is in the highlands of southern Mexico to Panama. This family includes 67percent of the world’s salamanders and, in the Appalachians, contains specieswith a wide diversity of life histories. The remaining salamander families arerelatively small, often containing only a handful of species. The newts aremostly Eurasian; the primitive hynobiids occur only in Asia; the torrent andPacific giant salamanders are found in the pacific Northwest; and two of thethree species of giant salamanders occur in temperate Asia. The remaining foursalamander families have their greatest diversity in eastern, temperature NorthAmerica, albeit not in the southern mountains. These families are the molesalamanders, amphiumas, mudpuppies, and sirens.
The newt cryptobranchid, molesalamander, and mudpuppy families are all represented in the Smokies. A muchmore detailed of the biogeography of North American amphibians is given byDuellman and Sweet (1999). Figure 5: Plethodontidae Figure 6: Hynobiids Figure 7: Newt CryptobranchidFigure 8: Mole Salamander Figure 9: Mudpuppy Figure 10: Mudpuppyc. SpeciesRichness in the SmokiesThere are 31 species ofsalamanders and 13 species of frogs that have been reported historically fromthe Great Smoky Mountains National Park. The Green Salamander may be extirpatedfrom the park and likely never was abundant.
The Northern Cricket Frog wasreported from the park based on records from Chilhowee, Tennessee (Huheey andStupka 1967), but probably never happened within park boundaries. The NorthernLeopard Frog may be extirpated, though there was a possible sighting in 2000. Morehistorical information on these species is found in their respective speciesaccounts (Dodd, 2004). Figure 11: Cricket Frog The remaining 40species are not distributed evenly throughout the Great Smokies.
Somesalamanders customarily are found only in the higher elevations, although theyare not, perhaps, as exclusively confined to these habitats as previouslybelieved. Others are lowland species. A few salamanders (black-belliedSalamander, Spring Salamander) span a great range of elevations.
Likewise, afew salamanders are found only in Tennessee, whereas others essentially arefound only in North Carolina (Three-lines Salamander). Some salamanders haveprofoundly restricted distributions within the park, reflecting specializedhabitat requisites, whereas others are widespread and occur in many types ofhabitats (Dodd, 2004). Figure 12: Black-belliedSalamander Figure 13: SpringSalamander Figure 14: Three-linesSalamander Undoubtedly, (Dodd, 2004) researches said that the recentamphibian distribution patterns are the outcome of a complex interaction ofevolutionary divergence, historical biogeography, and specialized habitatrequirements, even without considering the influence of humans. The interplaybetween evolution, geography, and ecology has resulted in a high speciesrichness of salamanders within the park, but the same is not true of frogs. Frogsrequire aquatic breeding sites, and these are scarce in the mountains,especially on the south and southwestern sides of the park. Hence, few speciesof frogs are found in the Smokies relative to the Atlantic Coastal Plain or theTennessee Valley. Thereare three non-human-related historical and biological factors that contributeto the high species richness of salamanders within the plethodontids opted forlife and shallow flowing streams.
Such habitats are still centers of salamanderdiversity. Naturalselection probably favored lung loss by larval protoplethodontids, and theevolution of narrow heads, in order to exploit Coastal Plain. The cool watersof the leaks still permitted sufficient oxygen diffusion to compensate for thelack of lungs, and terrestrial mating progressed as a method to facilitatecourting and sperm transfer.
A combination of morphological, physiological, andecological changes allowed salamanders to exploit the specialized ravine. As theAppalachians were subjected to regional up warps and faulting during the lateCenozoic era and as erosion took its toll, these combined factors created thepresent topography. During this time, early plethodontid salamanders wereisolated, which allowed genetic differentiation.
As a result of thisdifferentiation, associated physical isolation, and changes in climate, theplethodontid salamanders have undergone a steady process of speciation in thesouthern mountains- a process that continues today. Consequently, there is ahigh level of species richness in the Smokies and elsewhere in the SouthernAppalachians among the lungless salamanders. In addition, the evolution andradiation of the lungless salamanders can be found in Ruben and Boucot (1989),Regan and Verrell (1991), Beachy and Bruce (1992), Bruce et al (1993) and,Meand (2000). Figure 15: LunglessSalamander