Ambystomatidae

While originally the genus Dicamptodon and Rhyacotriton were under the family Ambystomatidae, these are now separated into their own families, leaving the genus Ambystoma as the only existing genus of the Ambystomatidae.

There are roughly 30 species of Ambystoma, most of which complete metamorphosis, and are strictly terrestrial and fossorial, which gave them the nickname of mole salamanders. However, some species like the Axolotl (Ambystoma Mexicanum) are obligatory neotenic, never completing metamorphosis and remaining in water their whole live. Other species instead, like the Ambystoma Tigrinum, are facoltative neotenic, with neotenic and metamorphosed specimen living together in the same population.

The Ambystoma are endemic of North America, from Alaska to Mexico. These salamanders have robust bodies, with thick limbs and tails. They are medium to large sized, reaching the 30 cm in length.

Despite their fossorial behaviour, these salamanders still need to return to the water to breed. Courtship and breeding for most species tends to occur in ponds in the spring, but two species (Ambystoma Cingulatum and Ambystoma Opacum) lay eggs on land, with Ambystoma Opacum practicing parental care, where the female leaves the eggs once the nesting side is inundated.

There also exist hybrid population consisting of only females, the oldest example of unisexual vertebrate. Unisex lineages are usually short lived and become extinct rapidly, which reinforces the theoretical advantages of sexual reproduction, but the lineage of female only Ambystoma hybrid has persisted for roughly 5 millions of years. These hybrid females mate with males of Ambystoma Jeffersonianum, Ambystoma Tigrinum, Ambystoma Laterale and Ambystoma Texanum, but surprisingly, the progenitors of these hybrids are not among the four species which they usually mate with, but originate from Ambystoma Barbouri. These females reproduces mostly via 2 main methods:

• Gynogenesis: which means that no genetic material from the male is used to develop the embryo, meaning that the offspring are clones of the mothers.
• Kleptogenesis: which means that the females incorporate part of the genomes from the males of compatible species into the eggs. This practise has the benefits of incorporating useful genes that may be better suited to the environment into the next generation.