Ambystoma macrodactylum

The long-toed salamander (Ambystoma macrodactylum) is a mole salamander in the family Ambystomatidae. This species, typically 4.1–8.9 cm (1.6–3.5 in) 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 2,800 m (9,200 ft). 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. 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. The body of the long-toed salamander is dusky black with a dorsal stripe of tan, yellow, or olive-green. This stripe can also be broken up into a series of spots. The sides of the body can have fine white or pale blue flecks. The belly is dark-brown or sooty in color with white flecks. Root tubercles are present, but they are not quite as developed as other species, such as the tiger salamander. The eggs of this species look similar to those of the related northwestern salamander (A. gracile) and tiger salamander (A. tigrinum). Like many amphibians, the eggs of the long-toed salamander are surrounded by a gelatinous capsule. This capsule is transparent, making the embryo visible during development. Unlike A. gracile eggs, there are no visible signs of green algae, which makes egg jellies green in color. When in its egg, the long-toed salamander embryo is darker on top and whiter below compared to a tiger salamander embryo that is light brown to grey above and cream-colored on the bottom. The eggs are about 2 mm (0.08 in) or greater in diameter with a wide outer jelly layer. Prior to hatching—both in the egg and as newborn larvae—they have balancers, which are thin skin protrusions sticking out the sides and supporting the head. The balancers eventually fall off and their external gills grow larger. Once the balancers are lost the larvae are distinguished by the sharply pointed flaring of the gills. As the larvae mature and metamorphose, their limbs with digits become visible and the gills are resorbed. The skin of a larva is mottled with black, brown, and yellow pigmentation. Skin color changes as the larvae develop and pigment cells migrate and concentrate in different regions of the body. The pigment cells, called chromatophores, are derived from the neural crest. The three types of pigment chromatophores in salamanders include yellow xanthophores, black melanophores, and silvery iridiophores (or guanophores). As the larvae mature, the melanophores concentrate along the body and provide the darker background. The yellow xanthophores arrange along the spine and on top of the limbs. The rest of the body is flecked with reflective iridiophores along the sides and underneath. As larvae metamorphose, they develop digits from their limb bud protrusions. A fully metamorphosed long-toed salamander has four digits on the front limbs and five digits on the rear limbs. Its head is longer than it is wide, and the long outer fourth toe on the hind limb of mature larvae and adults distinguishes this species from others and is also the etymological origin of its specific epithet: macrodactylum (Greek makros = long and daktylos = toe). The adult skin has a dark brown, dark grey, to black background with a yellow, green, or dull red blotchy stripe with dots and spots along the sides. Underneath the limbs, head, and body the salamander is white, pinkish, to brown with larger flecks of white and smaller flecks of yellow. Adults are typically 3.8–7.6 cm (1.5–3.0 in) long.