Pregnancy in Salamanders

Most salamanders are egg-laying, or oviparous, animals. Commonly, a salamander is pregnant for only a few days. It begins when the male deposits sperm via a spermatophore in the water. The female takes the sperm into her cloaca or genital opening. After her eggs are fertilized she deposits them in the water. The eggs, laid individually, attach to underwater structures where they'll have a reasonable chance of staying safe until they hatch. The axolotl (Ambystoma mexicanum) is a unique-looking aquatic salamander endemic to Mexico that follows this life cycle. In a few more primitive salamander species like the Japanese giant salamander (Andrias japonicus), egg fertilization takes place externally -- the female lays eggs and the male deposits sperm onto them.

Some terrestrial salamander species lay their eggs in moist, protected nests after fertilization. The pregnancy stage for these salamanders is short and about the same as for aquatic oviparous species. All species in the genus Bolitoglossa, the web-footed salamanders, skip the aquatic larval stage. All 120 species in this genus are terrestrial; a few are arboreal. Bolitoglossa pesrubra, a species common in the highlands of Costa Rica, lays one dozen to three dozen eggs at a time in a nest. They make nests usually in dark, moist places such as under a rock or rotting log. The mother and sometimes the father guard the eggs for four to five months until they hatch. The parent spends nearly all its time with its body wrapped around the eggs and its head resting on top of them. The eggs hatch into salamanderets -- very small adult-form salamanders -- rather than larvae.

Ovoviviparous salamander species fall somewhere between live-bearing and egg-laying species. In these animals, the mother salamander doesn't lay eggs; instead, they develop within her body. The eggs hatch into larvae inside the mother's body, which go through a typical development process until they reach the juvenile stage, when they resemble small adults. Arouss al ayn (Salamandra infraimmaculata), also called the Near Eastern fire salamander, is an ovoviviparous species. It relies on water to mate and produce offspring. The male and female mate in spring, fertilizing the eggs internally. The eggs develop within the female's body and are born as larvae 1 inch to 1 1/2 inches long. The mother salamander may give birth to 10 to 40 larvae in a reproductive season, with older females producing more offspring. The larvae are aquatic until they develop into juveniles, when they leave the water and live terrestrially.

Viviparity is rare among salamanders. In these animals, the fertilized eggs hatch within the mother's body and she gives birth to live young via her cloaca, the multipurpose opening used for reproduction and waste excretion. The female salamander gives birth in a protected, moist environment to keep the newborns safe. Viviparity is possible only among terrestrial and arboreal salamander species that have adapted not to depend on water bodies for any stage in their life cycle. Salamandra lanzai is a viviparous species. Lanza's Alpine salamander has an extremely long pregnancy period -- it lasts two to three years. After years of gestation the babies are born as salamanderets, about one to six per litter. The tiny amphibians immediately begin their lives as terrestrial salamanders.