The long-toed salamander (Ambystoma macrodactylum) is a mole salamander in the family Ambystomatidae. This species, typically long when mature, is characterized by its mottled black, brown, and yellow pigmentation, and its long outer fourth toe on the hind limbs. Analysis of fossil records, genetics, and biogeography suggest A. macrodactylum and A. laterale are descended from a common ancestor that gained access to the western Cordillera with the loss of the mid-continental seaway toward the Paleocene.
The distribution of the long-toed salamander is primarily in the Pacific Northwest, with an altitudinal range of up to . It lives in a variety of habitats, including temperate rainforests, coniferous forests, montane riparian zones, sagebrush plains, red fir forests, semiarid sagebrush, cheatgrass plains, and alpine meadows along the rocky shores of mountain lakes. It lives in slow-moving streams, ponds, and lakes during its aquatic breeding phase. The long-toed salamander hibernates during the cold winter months, surviving on energy reserves stored in the skin and tail.
The five subspecies have different genetic and ecological histories, phenotypically expressed in a range of color and skin patterns. Although the long-toed salamander is classified as a species of Least Concern by the IUCN, many forms of land development threaten and negatively affect the salamander's habitat.
Taxonomy
Ambystoma macrodactylum is a member of the Ambystomatidae, also known as the mole salamanders. The Ambystomatidae originated approximately 81 million years ago (late Cretaceous) from its sister taxon Dicamptodontidae. The Ambystomatidae are also members of suborder Salamandroidea, which includes all the salamanders capable of internal fertilization. The sister species to A. macrodactylum is A. laterale, distributed in eastern North America. However, the species-level phylogeny for Ambystomatidae is tentative and in need of further testing.
Systematics and biogeography
Evolutionary origins
The ancestral origins for this species stem from eastern North America, where species richness of ambystomatids are highest. The following biogeographic interpretation on the origins of A. macrodactylum into western North America is based on a descriptive account of fossils, genetics, and biogeography. The long-toed salamander's closest living sister species is A. laterale, a native to northeastern North America. Ambystomatidae was isolated to the southeast of the mid-Continental or Western Interior Seaway during the Cretaceous (~145.5–66 Ma). While three other species of the Ambystomatidae (A. tigrinum, A. californiense, and A. gracile) have overlapping ranges in western North America, the long-toed salamander's closest living sister species is A. laterale, a native to northeastern North America. It has been suggested that A. macrodactylum speciated from A. laterale after the Paleocene (~66–55.8 Ma) with the loss of the Western Interior Seaway opening an access route for a common ancestor into the Western Cordillera. Once situated in the montane regions of western North America, species had to contend with a dynamic spatial and compositional ecology responding to the changes in altitude, as mountains grew and the climate changed. For example, the Pacific Northwest became cooler in the Paleocene, paving the way for temperate forest to replace the warmer tropical forest of the Cretaceous. A scenario for the splitting of A. macrodacylum and other western temperate species from their eastern counterparts involves Rocky Mountain uplift in the late Oligocene into the Miocene. The orogeny created a climatic barrier by removing moisture from the westerly air stream and dried the midcontinental area, from southern Alberta to the Gulf of Mexico.
Ancestors of contemporary salamanders were likely able to disperse and migrate into habitats of the Rocky Mountains and surrounding areas by the Eocene. Mesic forests were established in western North America by the mid Eocene and attained their contemporary range distributions by the early Pliocene. The temperate forest valleys and montane environments of these time periods (Paleogene to Neogene) would have provided the physiographic and ecological features supporting analogs of contemporary Ambystoma macrodactylum habitats. The Cascade Range rose during the mid Pliocene and created a rain shadow effect causing the xerification of the Columbia Basin and also altered ranges of temperate mesic ecosystems at higher elevations. The rise of the Cascades causing the xerification of the Columbia Basin is a major biogeographic feature of western North America that divided many species, including A. macrodactylum, into coastal and inland lineages.