Introduction

Breeding Behavior

During the breeding season, male newts of most species will actively seek out females, and may become more aggressive and territorial during this time. The males of many species also develop dimorphic characteristics during the breeding season, such as large crests and tail fins (Triturus), smooth and lighter colored skin (Taricha), laterally compressed tails (Cynops, Paramesotriton, Notophthalmus, Taricha, etc.), bluish-purple or white sheen on the tail and body (Paramesotriton, Cynops, Neurergus, Triturus, etc.), nuptial pads for gripping females in amplexus (Notophthalmus), and more. 

The photo at top-right depicts a male Triturus vittatus ophryticus in breeding attire. He has developed an impressive dorsal crest and tail fin, as well as a whitish sheen along the tail. All of these seasonal characteristics are developed to attract the attention of the female, or to aid in the mating process. During the breeding season, females do not portray any spectacular characteristics, although some may develop more laterally compressed tails and smoother skin to better adapt to the months in the water. 

The actual mating process varies for different species, and can consist of a very complex display, long hours of amplexus, or simply the deposition of a spermatophore by the male and collection by the female. Male Triturus species are probably the most noted for their elaborate and complex mating display. This can consist of hours of tail-fanning and tail-whipping to waft pheromones toward the female, and manipulative movements to enhance the size of the dorsal crest. Interestingly, the elaborate display performed by Triturus species does not include amplexus at any point. Other newts, such as Taricha, Notophthalmus, and Pleurodeles species do not partake in such elaborate displays, but may remain in amplexus for several hours, with or without tail-fanning. Males of such species may develop nuptial pads, black corneous pads, on the front and/or hind extremities used to grip the female in amplexus. Males of other species, such as Cynops, may become increasingly aggressive, often chasing females and erratically tail-fanning. The photo at left shows a male Cynops ensicauda popei tail-fanning a female. 

Elaborate displays and amplexus both end in the same way, with the male depositing a spermatophore, often times manipulating the female to to pass over it and collect it with her cloacal lips. One very notable exception to the rule is the species Euproctus asper, which reproduces through direct cloacal contact. For more information about this amazing species, see the Calotriton asper database entry.

After fertilization and a short incubation period, female newts will begin depositing their eggs over the following weeks or months. Eggs may be attached singly to submerged vegetation or other objects, or simply deposited on the substrate. Others may deposit several eggs contained in one gelatinous protective shell, and some may produce strings of eggs. Many species, including those of the genera Cynops and Triturus, will deposit eggs singly to small-leaved vegetation or leaf tips, usually folding a part of the leaf over the egg with the back feet for protection. This can be seen in the photo at at right of a female Triturus cristatus, who is carefully folding a leaf tip over a freshly deposited egg. 

Females will produce several dozen to several hundred eggs in one season, usually depositing them a few at a time over a period several weeks or months. They produce so many eggs to counteract the high mortality rate in the wild, for newt eggs and young larvae are an easy and abundant food source for fish, insects, other amphibians, and even adult newts. Other mortality factors affecting newt eggs include genetic deformities, unstable environments, possible food shortages, pollution, and desiccation caused from drying water sources. 

Some species also show a degree of parental care for their eggs. Pachytriton females are known to aggressively guard their egg clutches, as are some Paramesotriton species. Oddly, some eggs of the fore mentioned species may also be consumed by the guarding parents. Most species, including Cynops, Notophthalmus, and Triturus, do not show any signs of parental care, and may consume eggs and small larvae if given the opportunity.

Ovoviviparous species produce eggs that develop internally, i.e. inside the mothers oviduct. The internal egg casing is reduced to a thin membrane upon delivery, and is usually broken through by the emerging larvae, making the birth appear live. Ovoviviparous adults, such as Salamandra salamandra, typically deliver their offspring directly into a water source. 

Other caudate species are  viviparous. Viviparity occurs when the development of internal eggs is prolonged even further than with ovoviviparity, causing the larvae to emerge from their casings internally, and continue development to metamorphosis within the mothers oviduct. Viviparous young are able to exchange gases, waste products, and nutrients from the mothers blood, whereas ovoviviparous species are capable only of limited gas exchange across the egg membranes. A placental-like infolding of the oviduct and egg membranes may also develop in advanced viviparity. 

Viviparous amphibians, such as Salamandra atra, usually only produce one or two offspring out of a clutch of 20-30, which are delivered as fully morphed, miniature adults. The remaining, unfertilized eggs provide nourishment to the developing larvae when their yolk sacs have been exhausted. The larvae of Salamandra atra obtain further nourishment by scraping the mothers reproductive tract with specialized teeth, which provides them with enough nourishment to last through the 2-4 year gestation period.  Similar behavior is also observed in some populations of Salamandra salamandra, but with a slight twist; after all the unfertilized eggs have been consumed, some developing larvae may cannibalize other developing larvae within the mothers oviduct. All larval development occurs within the mother, making these species true terrestrials. 

Viviparity is also observed in the genus Mertensiella. M. luschani antalyana, in particular, produce young in a similar fashion to Salamandra atra, however, the gestation period is usually only one year. On the other hand M. luschani's close relative, M. caucasica, produce eggs on land after an aquatic courtship. *Note: Mertensiella luschani is often considered a member of the genus Salamandra, i.e. Salamandra luschani, and recently has been placed into its own genus, Lyciasalamandra, and some subspecies moved to species level under this genus.

Some would argue the validity and definitions of ovoviviparous and viviparous when applied to caudates, and often times only the terms oviparous and viviparous are used to differentiate between egg laying and "live-bearing". The existence of some ambiguity between viviparous and ovoviviparous amphibians is generally accepted in practice today.  

Ovoviviparity and viviparity, or whatever terminology is preferred, are thought to be adaptations to the extreme seasons encountered in mountainous regions. At high altitudes, suitable development periods for larval amphibians may simply be too short for survival. This problem is resolved with internal development by eliminating or reducing the time larvae develop in the external climate. The same can apply to those species found in very dry areas, where rainfall may be severely limited. Another factor to consider is the abundance of aquatic food supply for larvae, which may be inadequate in some areas, and the pressures of predation from other animals. In general, ovoviviparity and viviparity are associated with the climatic and geological surroundings, which may inhibit larval development for multiple reasons. However, there are some holes in this theory, as some species seemingly do not encounter such environments, and so the advantages of ovoviviparity or viviparity for such species are unknown. Also, the mother puts herself at considerable risk of predation by carrying around such a heavy load, and considerably less offspring are produced compared to the hundreds of eggs produced by oviparous species every season. In summary, the advantage of, and reason for viviparity and ovoviviparity are unknown for every species, but it is assumed that the advantages of such development practices outweigh the disadvantages in all cases.

Egg Development of Biphasic Species

Typical biphasic newts deposit eggs in water sources such as vernal pools, permanent ponds and lakes, streams, ditches, and ponds, depending on the species. Female newts may deposit one or more eggs at a time, over a period of several weeks or months. Some species attach eggs individually onto plant leaves, often folding the leaf over for protection, while others may produce clumps of 10-30 eggs and simply place them on the substrate. Stream-dwellers typically deposit eggs on the undersides of rocks and wood where they will not be swept away with the moving water. When eggs are first deposited, they will swell up with water within a few hours. Eggs may take anywhere from a few weeks to a few months to hatch, depending on the species and surrounding environment. In general, eggs deposited in sunlight typically possess melanin, a skin pigment that resists the effects of UV lighting, whereas those placed in the shade lack melanin. There are some exceptions, such as Euproctus asper populations at high elevations, whose eggs may also contain melanin, although they are typically placed in dark caves. The melanin found in eggs is thought to serve the same purpose as in adults; protection from UV exposure and heat retention. 

New amphibian eggs consist of several layers, with the outer layers comprised of a gelatinous envelope surrounding a core of undeveloped embryonic components. Freshly deposited eggs appear as little cream colored balls, and quickly swell with water. At later stages, near hatching, the embryo can be seen clearly through the egg casing. The photos above-right and above-left show eggs at different stages of development. The top-left photo shows a newly deposited Cynops orientalis egg, and the photo at right shows a near-hatching Triturus carnifex egg. The Cynops orientalis photo was take a few hours of deposition, when the egg has just swelled with water. In the Triturus carnifex photo, the tiny larvae can be seen clearly through the egg casing. When newt eggs hatch, the larvae have yolk sacs attached to their undersides, which will provide them with adequate nourishment for the first few days life. When the yolk sac is fully absorbed, the larvae will begin seeking out micro-foods such as daphnia, copepods, insect larvae, etc. The illustration below depicts a typical amphibian egg, one hour after deposition. 

Newts usually produce 100 or more eggs in a season to counteract their high mortality rate. Although some eggs may possess toxins, the eggs of most species are preyed upon by fish, crustaceans, other amphibians, and even members of the same species. T. cristatus, T. carnifex, T. dobrogicus, T. karelinii, T. marmoratus, and T. pygmaeus possess an abnormality in larval development that results in the termination of 50% of all eggs produced each season. In these species, half of the offspring produced stop developing around the time the tail begins to develop, or shortly after, and the embryo spontaneously aborts. This occurs as a result of the method in which chromosomes combine after fertilization. Of the twelve pairs of chromosomes in newt cells, the pair in Cell No. 1 differ from each other, and have been labeled 1A and 1B. These are the chromosomes that pass into the gametes (sex cells; eggs and sperm) of the parents. In the normal instance, one chromosome, either 1A or 1B, is contributed by each parent, so that the combination is always 1A + 1B. The chromosomal abnormality occurs when the chromosome contributed are of the same type, that is, when the combination is 1A + 1A, or 1B + 1B. The evolutionary aspects of this anomaly are as of yet undetermined.

For more information on egg development, see the Amphibian Biology section.

Most newt larvae are very small, and very quick in the water. Upon hatching, larvae are only a few millimeters in length, and lack front and hind extremities. Upon metamorphosis, larvae have developed distinct extremities, coloration, and caudal characteristics. Pond type larvae are physically adapted for slow moving, oxygen-poor waters, and possess long gills, tall tail fins, and longer digits. Stream type larvae are more streamlined, with shorter gills, low tail fins to decrease drag, and stubby digits.

The photos in this section show two species at different stages in larval development. At top-right is a photo of a newly hatched larva of Triturus alpestris. At this stage, the limbs, tail, and gills are noticeably underdeveloped. The photo at top-left, of Tylototriton shanjing, shows a more advanced larva near metamorphosis. In the advanced stages, the larva possess distinguishable extremities and digits, more pronounced head and abdomen, distinctive coloration, and larger, bushy gills.  

Metamorphosis, Neoteny, and the Juvenile Stage

The coloration of juveniles is sometimes similar to the adults, and sometimes drastically different, depending on the species. Notophthalmus viridescens viridescens efts possess distinctly different coloration than their adult counterparts. These efts, sometimes called Red Efts, are vivid red-orange, whereas the adults are an understated tannish-green. The bright coloration of the efts is thought to be a form of aposematic coloration used to clarify their high toxicity level (nearly 10 times that of the adults). In fact, some sympatric species, including Pseudotriton ruber, are thought to mimic the coloration of Notophthalmus viridescens efts in an attempt to fool predators into thinking they are highly toxic, like the efts, even though they are not. Other species, such as Triturus marmoratus, may possess coloration very similar to their adult counterparts, although they are typically more vivid. Some species, such as the more colorful Cynops species, may develop adult coloration and pattern characteristics rather slowly, as they mature. The photo at left shows a vivid red eft, Notophthalmus viridescens. See the special section below on for physical comparisons of Notophthalmus viridescens and Triturus marmoratus juveniles to typical adults. 

Many newts go through a terrestrial phase immediately after metamorphosis, whereas others may remain aquatic or semi-aquatic. Terrestrial phase young are called efts, subadults, or juveniles. The eft phase may last anywhere from 1.5-8 years, depending on the particular species, after which the newt reaches sexual maturity and assumes a semi-aquatic lifestyle, or begins annual breeding migrations. Some common genera that go through a terrestrial juvenile stage are Notophthalmus, Cynops, Taricha, Triturus, and Neurergus. Notophthalmus efts are often noted in literature pertaining to amphibians because of their remarkable red coloration and other drastic differences from the semi-aquatic adult phase. Notophthalmus efts are typically strictly terrestrial, whereas other species may show some ambiguity in certain environments. For example, most juvenile Cynops are generally regarded as terrestrial, but may adapt well to a semi-aquatic environment in captivity.

Terrestrial juveniles possess physical characteristics that are more suited for an existence on land, including stronger hind legs to support the weight of the body, thicker, and rougher skin, modified vision to see through atmospheric air, and a more cylindrical tail. When terrestrial juveniles return to the water, whether it is a permanent or annual event, the physiology changes to adapt better to a more aquatic life, including more permeable skin to absorb oxygen in the water, modified vision to detect movements through murky or clouded water, and a more laterally compressed tail to aid in swimming. Interestingly, juveniles are typically more toxic than their adult counterparts. Notophthalmus viridescens efts are nearly 10 times as toxic as adults, which is the general trend for other eft-adult species relationships.

 The following tables show a select few juvenile and adult newts for physical comparison. The photos show that some species are very similar to their adult counterparts, whereas others are very different in appearance. For more photos of young, larvae, and eggs, see Embryonic, Larval, and Young Amphibians.

Cynops orientalis morph (top) and adult female (bottom).	Cynops ensicauda popei juvenile (top) and adult male (bottom).	Notophthalmus viridescens viridescens eft (top) and adult (bottom).

Cynops pyrrhgaster juvenile (top) and adult male (bottom).	Triturus marmoratus juvenile (top) and adult male (bottom).	Neurergus strauchii juvenile (top) and adult male (bottom).

References

Shi, Yun-Bo. Amphibian Metamorphosis: From Morphology to Molocular Biology. John Wiley & Sons, 1999.