Newts
Newts
Newts are lizard-shaped animals with a tail in the amphibian order Caudata (or Urodela), in the suborder Salamandroidea, which also includes the salamanders. The distinction between newts and salamanders is not always obvious since both have a tail in the larval stage and the adult stage. However, newts do not have costal grooves on the sides of their body, they are less slippery than salamanders, they have a unique dentition on the roof of the mouth, and they tend to be more aquatic than salamanders.
Biology of newts
Like salamanders, newts have a complex life cycle, the stages of which are egg, larva, and adult. Some species of newts can be distinguished from salamanders in that the newts have two distinct adult stages.
In the case of the red-spotted newt (Notophthalmus viridescens ) of North America, the red eft is the stage that occurs after transformation of the aquatic larva. The red eft is bright red or orange, and is a pre-reproductive adult stage. The red eft wanders widely in forests, sometimes for several years, and is most commonly found on moist nights. Eventually, the red eft migrates to an aquatic habitat, changes to a yellowish color, develops a broad, adult tail fin, and becomes a sexually mature, breeding adult. The migration of red efts to water has been shown to be stimulated by the presence of the pituitary hormone prolactin.
Not all populations of red-spotted newts display this type of life cycle, for some coastal populations bypass the terrestrial red eft stage, and produce breeding adults directly from larvae. These adults may retain some larval characteristics, such as gills, which is an example at neoteny, or paedomorphosis.
Courtship in some species of newts involves elaborate aquatic displays by the male. These displays are designed to entice the female newt to pass over sperm-containing spermatophores that the male has previously deposited onto the surface of the sediment. If the male is successful, the female newt picks up the spermatophore with her cloacal lips and stores the spermatophore internally, which then fertilizes her ova as they are laid singly on surfaces in the aquatic habitat.
The red eft stage of the red-spotted newt contains toxic, bad-tasting chemicals in its skin. As a result, many potential predators learn to avoid this animal, and will not eat red efts. The range of the red salamander (Pseudotriton ruber ) overlaps part of the larger range of the red-spotted newt in the eastern United States. It appears that the superficially similar but non-toxic red salamander may be a mimic of the color of the red eft, taking advantage of the fact that many predators avoid this animal as food.
Newts have been shown to have a keen ability to find their way home to their natal or home pond. After they were displaced during an experiment, red-bellied newts (Taricha rivularis ) studied in California proved to be capable of returning to their home stream within only one year, over a distance of up to 5 mi (8 km).
Species of newts
Newts in the genus Notophthalmus are found in eastern North America, while species of Taricha are found in the western United States. The most common of the eastern newt is the red-spotted newt (Notophthalmus viridescens ), which has a wide distribution in the eastern United States and southeastern Canada. The striped newt (N. perstriatus ) occurs only in northern Florida, while the black-spotted newt (N. meridionalis ) occurs on the Gulf coast of Texas and northern Mexico. The most widespread species of western newt is the rough-skinned newt (Taricha granulosa ) of the coastal states and British Columbia. The California newt (T. torosa ) occurs in coastal California and southern Oregon, while the red-bellied newt has a relatively restricted distribution in northern, coastal California.
The most common newts of temperate parts of Eurasia are animals in the genus Triturus, for example, the smooth newt (Triturus vulgaris ), the crested newt (T. cristatus ), and the alpine newt (T. alpestris ). These newts do not have an eft stage, although the adults may spend some time on land. The mountain newts (Euproctus spp. ) are another European group of newts.
Newts and people
Newts have little direct economic value, other than sometimes being kept as unusual pets. The value of newts derives from the fact that they are ecologically important in their natural communities and that they have an interesting biology.
Although little is known about the conservation status of newts, most species of newts in North America are not endangered. However, the amount and quality of their habitat in many places has declined greatly because of human influences, and this has caused local populations to decrease. Like so many other aspects of our natural, ecological heritage, it is important that the population status of newts be monitored to ensure that they do not become endangered as a result of the activities of humans.
KEY TERMS
Complex life cycle —A life marked by several radical transformations in anatomy, physiology, and ecology.
Metamorphosis —This refers to the great anatomical and physiological transformations that occur during the life of some animals.
Neoteny —The retention of juvenile characteristics in sexually mature adult animals.
Resources
BOOKS
Bishop, S.C. Handbook of Salamanders. New York: Cornell University Press, 1994.
Conant, Roger, et al. A Field Guide to Reptiles & Amphibians of Eastern & Central North America. Boston: Houghton Mifflin, 1998
Hofrichter, Robert. Amphibians: The World of Frogs, Toads, Salamanders and Newts. Toronto: Firefly Books, 2000.
Zug, George R., Laurie J. Vitt, and Janalee P. Caldwell. Herpetology: An Introductory Biology of Amphibians and Reptiles. 2nd ed. New York: Academic Press, 2001.
Zweifel, R.G., H.G. Cogger, and D. Kirshner, eds. Encyclopedia of Reptiles and Amphibians. 2nd ed. Academic Press, 1998.
Bill Freedman.