NATURAL HISTORY DISCOVERY
DAYS
NEWT WORLD NEWT WORLD
NEWT WORLD
NEWTS
Newts are a kind of water-breeding salamander. Newts evolved from other salamanders about 60
million years ago. Today newts are found
in the temperate parts of
ROUGH-SKINNED NEWT
- Distribution.- The Rough-skinned newt (Taricha granulosa) is found only in
the
- Habits.- Adult newts live in forests, away from ponds, from November until February. In February, the adults migrate to ponds for mating and egg-laying. Some adults stay in the pond until November, then they migrate back to the forest. Other adults remain in the pond all year long.
- Food.- In the forest, newts feed on earthworms and insects. In the pond, newts feed on snails and aquatic insects.
- Males and females.- During the breeding season (February – April) it is easy to tell the male from the female. The male is larger than the female. The male has smooth skin, a tall tail, and black friction pads on the soles of his feet (Fig. 1). The female has rough skin that is dark reddish brown in color.
Figure 1. Underside of the male newt, showing dark
friction pads on the soles of his feet.
From Stebbins 1962. Figure 2. A pair of newts in
amplexus. The male is above; the female is below.
- Mating behavior. – Mating takes place underwater and follows a sequence of steps.
- Capture. - The male captures the female with his front legs. He rides on her back holding her with all four limbs. This posture is called amplexus (Fig. 2).
- Amplexus.- During amplexus, the male rubs his chin on the female’s nose (Fig. 3) and twitches his hind feet. Other males may attempt to capture the female while the male holds her in amplexus. To avoid these rival males, the amplexing male may swim away while holding on to the female. During amplexus, the female may signal to the male that she is not ready to mate by holding her head down. If she persists with this signal, the male may dismount and search for another female. After 1-4 hours, the female may signal to the male that she is ready to mate by holding her head up.
Figure 3. A male newt rubbing his
chin on the female’s nose during amplexus. From
- Making a spermatophore.- The male responds to the female’s head-up signal by dismounting and depositing a spermatophore on the ground in front of the female. The spermatophore is a small (1 cm high) but complicated structure that holds a spherical mass of sperm (Fig. 4).
Figure 4. A Taricha spermatophore.
Rear view on left; side view on right. The sperm mass is labeled S. From Zeller 1905.
- Sperm transfer.- If the female is receptive, she moves her body over the spermatophore and the sperm mass clings to her genital opening. After a successful sperm transfer, the male may capture the female again, so that steps 1-4 are repeated.
- Egg-laying.- The female stores sperm from 1-3 males inside her body. She uses the sperm to fertilize eggs just before they are laid. Eggs are laid a few days after sperm transfer. Typically the female lays several eggs each day. She lays a total of about 300 eggs during a breeding season. Eggs may be attached to branches or roots underwater (Fig. 5). Alternatively, the female may wrap the leaf of an aquatic plant around each egg as it is laid. This wrapping protects the egg from predators.
Figure 5. A female newt laying
her eggs. From
Stebbins & Cohen 1995.
- Larvae.- Small larvae with bushy gills hatch from the eggs. At first, the larvae have only front legs. When they get bigger, they develop hind legs as well. The larvae feed on aquatic insects and crustaceans.
- Young newts. In September, the larvae lose their gills, develop rough skin and walk out of the pond onto land. They now resemble the adults but are much smaller (two inches long). Over the next several years, the young newts live in the forest, eating worms and insects. When they reach adult size, they return to the pond to breed.
- Predators.- Young and adult newts are protected from most predators by powerful toxins (tetrodotoxin) in their skin. Because of these toxins, newts are avoided by most bird and mammal predators. Some garter snakes, however, are resistant to newt toxins. They can eat newts without any problems. Garter snakes are thought to be the major predators of newts.
- Newt safety – The same toxins that protect newts from predators can irritate your eyes, nose and mouth. It is safe for you to carefully handle newts, but you should wash your hands afterwards and avoid touching your nose, eyes and mouth.
REFERENCES
Arnold,
S.J., 1977. The
courtship behavior of North American salamanders with some comments on
Brodie, E. D., Jr., B. J. Ridenhour, and E. D. Brodie III. 2002. The evolutionary response of predators to dangerous prey: Hotspots and coldspots in the geographic mosaic of coevolution between garter snakes and newts. Evolution 56:2067-2082.
Houck, L. D. and S. J. Arnold. 2003. Courtship and mating
behavior. Pp. 383-424 IN: D. Sever (ed.), Reproductive Biology and
Phylogeny of Urodela. M/s
Science Publications,
Propper,
C.R. 1991. Courtship in the
rough-skinned newt Taricha granulosa.
Animal Behaviour. 41:547-554.
Jones, A. G., E. M. Adams and S. J. Arnold. 2002. Topping off: a mechanism of sperm competition in a vertebrate. Proc. Natl. Acad. Sci. U.S.A. 99: 2078-2081.
Jones, A. G., J. R. Arguello and S. J. Arnold. 2002. Validation of Bateman’s principles: a genetic study of sexual selection and mating patterns in newts. Proc. Roy. Soc. London B. 269: 2533-2539.
Stebbins, R. C.
1962. Amphibians of
Stebbins, R. C. & N. W. Cohen. 1995. A Natural History of Amphibians.
Titus, T. A. and A. Larson. 1995. A molecular phylogenetic perspective on the evolutionary radiation of the salamander family Salamandridae. Systematic Biology 44:125-151.
Zeller, E. 1905. Untersuchungen über die Samenträger und den Kloakenwulst der Tritonen. Zeitschrift für wissenshaftliche Zoologie 79: 171-221.
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