Tiger Salamander Complex
The presence of neotenic populations near those with large larvae has made it difficult to identify mole salamander species. The Tiger Salamander complex used to be considered a single species ranging from Canada to Mexico, falling under the name A. tigrinum. Despite differences in coloration and larvae, Tiger Salamanders were found throughout their unbroken range, which made it difficult to delineate subspecies, let-alone elevate any populations to species status. In morphological terms, Tiger Salamanders are all very similar, with large heads, small eyes, and thick bodies. This is probably because Tiger Salamanders have the primitive morphology of mole salamanders. They are also the largest of the mole salamanders, and have very large larvae. All populations have similar lifestyles and life-cycles are identical. However, when one looks at Tiger Salamander populations that were distant from each other, it becomes apparent that there are different species within this complex. The problem is that the ranges of these potential species overlap, and hybridization occurs, blurring the lines between species.
Several subspecies of A. tigrinum were named to deal with this problem. Recently, the Barred Tiger Salamander (A. mavortium) was elevated to species status—covering the Tiger salamander populations in the western and central United States. Several distinct subspecies still exist in A. mavortium, which may be elevated to species status at some point in the future. The California Tiger Salamander (A. californiense) has also been elevated out of A. tigrinum, and is actually very distantly related to all other mole salamander species. The Plateau Tiger Salamander (A. velasci) was elevated out of A. tigrinum through genetic analysis in 1997. All accounts referring to the Axolotl (A. mexicanum) as a close relative of A. tigrinum are now considered wrong, as they are now separated by both geography and many species between. Instead, it is A. velasci which shares the Axolotl's habitat, and is probably closely related to it. The Plateau Tiger Salamander was probably the parent of most of the neotenic species, which raises the possibility that A. velasci is paraphyletic, and may be broken up into more species in the future.
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