REPRODUCTION IN TRITURUS

LIFE CYCLE

Newts of the genus Triturus follow the familiar cycle of amphibian reproduction; they enter waterbodies to breed in the spring, and lay eggs which hatch into 'tadpoles'. The 'tadpoles' then metamorphose later in the season, and the young newts leave the water until they are old enough to breed.

BREEDING

The genus Triturus shows a remarkable degree of sexual dimorphism, and males may appear strikingly different from females. When in breeding condition, males of most species develop crests on their backs and tails, and may also become more brightly coloured than when on land. Their cloaca also becomes heavily swollen. Females usually appear very fat, as they may be carrying up to 400 eggs.

Unlike most frogs and toads, these newts lack a courting embrace (amplexus). The males, after a courtship 'dance' deposit a package of sperm (a spermatophore) on the substrate, and lead the female over it. She then takes the spermatophore into her cloaca, and fertilization takes place internally.

There are several elements to the courtship dance. These have been described by Arntzen & Sparreboom (1989), and vary from species to species. The display of T. vulgaris, T. helveticus and T. montandoni is diagramatically represented to the right, as shown in Arntzen and Sparreboom's paper.

The main elements are orientation, static display, retreat display and spermatophore transfer. In the orientation phase, the male positions himself in front of the female, after having ascertained that she is a female of his species. In the static display phase, he attracts her attention by means of body, tail, and crest movements. If she approaches him, he may move into the retreat display phase, continuing to display while maintaining his position relative to the female. When the male receives the signal that the female is ready, they will move into the spermatophore transfer phase, where the male deposits a spermatophore, and leads the female into the correct position to take it into her cloaca.

Static and retreat display elements are described by Arntzen and Sparreboom as:

'Fan': the male folds his tail back along the side nearest to the female he is displaying to, and beats it rapidly.
'Wave': the male holds out his tail to give the female a view of one side of his body and tail.
'Whip': the male violently lashes his tail against his side, to send a wave of water towards the female.
'Flick': an outward curling movement of the tail, less rapid and controlled than the 'fan'.
'Lean-in': the male stretches his legs, and slightly arches his back, to lean over the female.
'Cat-buckle': arching of the back. The 'lean-in' incorporates a 'cat-buckle'.
'Rocking': a complex movement, involving rocking from side to side, while coiling and uncoiling the tail on alternate sides.
'Head-bobbing': a rapid bobbing up and down of the head, which also causes vibration of the crest.
'Flurry': a rapid vibratory movement of the tail to the side facing away from the female.
'Wiggle tail bent': a slow worm-like undulation of the tail tip.
'Flamenco': a raising of the tail to an almost vertical position, with a wiggling of the tail tip.

Spermatophore transfer phase elements are described as:

'Creep': the male walks slowly in front of the female, with his body close to the ground, and his head slightly raised, undulating his tail.
'Touch-tail': the female touches the male's tail with her snout. This is the trigger for spermatophore deposition.
'Brake': after spermatophore deposition, the male creeps forward, then turns to one side, with his tail against his body, undulating the tip. This blocks the female's movement.
'Push-back': in the 'brake' position, the male pushes the female back slightly, by a small straightening of his tail.

After fertilization, the female will begin to lay eggs; these are usually laid singly, on the leaves of water plants, which are then wrapped around the egg. The sticky egg will 'glue' the leaf around it, thus hiding the egg from predators. In the absence of water plants, eggs may be laid on any available surface. Egg laying may last from from a week to several months.

DEVELOPMENT

An egg may take up to a few weeks to hatch, depending on temperature, and a tiny, slim-bodied larva (although the word 'tadpole' is sometimes used to describe newt larvae, this word is really only applicable to frog and toad larvae) will emerge. Newt larvae are almost exclusively carnivorous, and will feed on anything that moves, and will fit inside their mouths. The larvae look somewhat similar to fish in shape, but have large feathery gills on each side of their head. Over a period of a few months, they will grow legs (front legs first, unlike frog and toad larvae), and eventually will lose their gills, start breathing air, and will leave the water. Occasionally, some larvae will fail to metamorphose in this manner, and keep on growing in the larval stage. This is known as 'neoteny'.

NEOTENY

Neoteny is the retention of juvenile characters into the adult stage of life. This is occasionally seen in some Triturus species, particularly T. alpestris and T. vulgaris. The most obvious manifestation of neoteny is retention of gills in the adult, necessitating a totally aquatic lifestyle. Some neotenous newts become sexually mature, and are able to reproduce (total neoteny).

REFERENCES

Arntzen, J. W. & Sparreboom, M., 1989. A phylogeny for the Old World newts, genus Triturus: biochemical and behavioural data. J. Zool., Lond. 219: 645-664.