Has the Tiger Salamander Found the Fountain of Youth?
By Kris Kendell, ACA
The tiger salamander (Ambystoma mavortium) is one of Alberta’s 2 salamander species belonging to the Mole Salamander family (Ambystomatidae). Secretive by nature, they often emerge for only brief periods during rainy weather; or as they make their way to breeding ponds in the spring and disperse from them in the fall. The tiger salamander is larger than its relative, the long-toed salamander (Ambystoma macrodactylum), Alberta’s other salamander species. Tiger salamander adults are about 15 – 25 cm long, although slightly larger specimens do exist. They are found in the aspen parkland and prairie ecoregions of Alberta in small animal burrows, under objects near water, and burrowing in loose soil.
Failure to launch
Normally, the tiger salamander undergoes the usual spring ritual of breeding followed by the metamorphosing of larvae into smaller versions of the adults. However, occasionally larvae fail to transform into adults and become sexually mature while keeping their feathery external gills, wide dorsal and ventral tail fins and other larval features. This is known as neoteny. It is most common in salamanders from the family Ambystomatidae.
Depending on the family and species of salamander, neoteny can be permanent or temporary. It is frequently attributed to genetics and specific environmental conditions such as water temperature, water chemistry and food availability. Ambystoma species found at high elevations or in waterbodies with low temperatures often exhibit slowed or delayed transformation. Low temperatures affect the compound thyroxin, which is essential for transformation.
The good life
Neotenic tiger salamanders are often associated with alkaline waterbodies without predatory fish. These waterbodies usually possess enormously rich and plentiful food sources for the larva, reducing the need to transform into terrestrial adults. Another factor that favours an aquatic existence and suppresses transformation is inhospitable environmental conditions on land, such as arid conditions, lack of cover, shortage of food and competition with other species.
So how does one determine if a tiger salamander larva is an actual neotenic or simply a larva that has yet to transform? Although exceptionally large larval size may simply reflect favourable growing conditions, such as warm water temperatures and an abundance of food, it still remains one of the best indications of neoteny. Tiger salamander larvae that approach 30 cm in total length can be considered neotenic and sexually mature. Normally transformation in these larval salamanders can only be triggered by the introduction of environmental stresses like altered water chemistry or less favourable aquatic conditions.
While the tiger salamander may not have found the fountain of youth, in some cases they have found their fountain of youth. In Alberta there are several confirmed cases of neotenic tiger salamanders inhabiting various waterbodies. The environmental conditions responsible for these cases are still under scientific investigation. It is hoped that through continuing research and increased public involvement in reporting occurrences, we will better understand this fascinating phenomenon.