Ambystomid Salamanders: The Mole Salamanders of North America
Ambystomid salamanders are a group of about 30 species of salamanders that belong to the family Ambystomatidae. They are endemic to North America, ranging from Southeast Alaska and Labrador to the southern edge of the Mexican plateau. They are also known as mole salamanders because they spend most of their lives underground in burrows, emerging only to breed in ponds or streams.
Ambystomid salamanders are stout-bodied and have thick tails, robust limbs, smooth and shiny skin, and often bright color patterns. They have wide, protruding eyes and prominent costal grooves along their sides. They have the most derived pattern of spinal nerves among salamanders, and their diploid number is 28 chromosomes.
Most ambystomid salamanders have a biphasic life cycle, with aquatic larvae and terrestrial adults. The larvae have three pairs of external gills behind their heads and large caudal fins that extend from their heads to their tails and cloacae. They grow limbs soon after hatching, with four toes on the front legs and five toes on the hind legs. Their eyes are wide-set and lack eyelids. The larvae of some species can reach their adult size before undergoing metamorphosis.
Metamorphosis involves the loss of gills and fins, the development of lungs, eyelids, thicker skin, and limbs, and a change in coloration and behavior. The adults live in moist habitats under logs, rocks, or leaf litter, or in burrows made by themselves or other animals. They feed on various invertebrates, such as worms, insects, spiders, and snails. Some northern species may hibernate in their burrows during winter.
Some ambystomid salamanders are neotenic, meaning they retain their larval features and aquatic lifestyle as adults. The most famous example is the axolotl (Ambystoma mexicanum), which lives in the lakes of central Mexico and is widely used in research due to its ability to regenerate limbs and organs. Neoteny can be induced or reversed by manipulating the hormone thyroxine, which controls metamorphosis.
Another interesting feature of some ambystomid salamanders is their mode of reproduction. Two species (Ambystoma laterale and Ambystoma jeffersonianum) are gynogenetic triploids, meaning they have three sets of chromosomes instead of two. They are all female and produce offspring by mating with males of related species, but the sperm does not contribute any genetic material to the eggs. This results in clones of the mother with some variation due to recombination.
Ambystomid salamanders are important members of the ecosystems they inhabit, as both predators and prey. They are also indicators of environmental health, as they are sensitive to pollution, habitat loss, disease, and climate change. Some species are endangered or threatened by these factors, while others are more adaptable and widespread. Ambystomid salamanders are fascinating creatures that deserve our attention and conservation.