Amphibians

The family Ambystomatidae or “the mole salamanders” is included within the four earliest or most primitive family lineages of the order “Caudata” (the salamanders), diverging from all other salamanders in the Early Cretaceous period over 140 million years ago, around five million years before the koala and dolphin lineages diverged from their common ancestor. The small number of species that represent the genus Ambystoma are highly evolutionarily distinct members of both the salamanders and the amphibians as a whole.

Anderson’s salamander exhibits some highly unusual and distinct features, indicative of its evolutionary distinctiveness, including its rare “neotenous” life history, whereby the species never develops into an adult but instead retains its juvenile characteristics throughout life, essentially achieving reproductive maturity whilst still in its undeveloped larval form. There are a couple of theories for why neoteny (also referred to as paedomorphosis) develops in some mole salamanders. One idea is that the production or effectiveness of the hormone thyroxine is compromised, either by the species living in water bodies containing insufficient iodine (which is required in the manufacture of thyroxine by the body) or in water temperatures that are too cold for the thyroxine to be effective. This impacts upon the development of the species and sexually mature adults never develop adult characteristics but remain in the larval form. A second theory suggests that species evolving in pools surrounded by hostile terrestrial environments develop aquatic lives to obviate the need to exit the relative safety of their watery home. This is a common trait in species that inhabit high-elevation ponds.

Anderson’s salamander is an Ambystomatid or mole salamander found only in Lake Zacapu near Zacapu, Mexico at an elevation of 2,000 meters above sea level. Mole salamanders are medium to large, stocky salamanders, usually measuring between 90 to 350mm from the tip of the nose to the end of the tail, which salamanders retain throughout their life. Males are often larger than females, owing to their longer tails. Ambystomatids generally exhibit both aquatic “neotenic” larval (or aquatic and permanently juvenile in form with external, feathery gills) and terrestrial “metamorphosed” (or ground-dwelling, fully developed adult in form with reduced gills) stages in their wild populations. Ambystomatids are often boldly patterned as adults, with well-developed “costal” grooves (successive vertical grooves along the sides of the body), especially the metamorphosing varieties. They have a rather flattened body with a wide, flattened head, a large mouth and smooth skin with many glands. The tail is roundish or laterally compressed, and, during the breeding season, males have a very swollen cloacal zone (the region around the reproductory and excretory opening in amphibians located underneath the base of the tail).

Like all neotenic Ambystoma species, Anderson’s salamander retains its larval features into adulthood. The mature salamander has medium-sized external gills with bright red filaments, and a prominent caudal (or tail) fin. It grows to a length of around 214 mm, with the tail accounting for about 40% of this measurement. A dorsal fin extends as a low ridge from the base of the gill rakers along the back to the base of the tail, where it rises about 13 mm to form the dorsal tail fin. This species has a large head and small, stocky limbs, as do the larvae. The toes are short and pointed with a slight degree of webbing. The skin colouration is a complex pattern of black blotches (some interconnected) on a red-brown base.

Lake Zacapu (Lago Zacapu) and its surrounding streams near Zacapu, located in north-western Michoacan within the Mesa Central portion of Mexico at an altitude of 2000 metres above sea level.