About Ascaphus truei Stejneger, 1899
The most recognizable trait that sets tailed frogs (Ascaphus truei) apart from all other frog species is the visible "tail" appendage. This species is typically classified in the ancient frog suborder Archaeobatrachia, and forms a basal clade with the New Zealand primitive frog genus Leiopelma. This clade is considered the sister taxon to all other frogs. The "tail" is only present in males, and is actually a modified part of the cloaca that is used to insert sperm into females during mating. This structure improves breeding success by minimizing sperm loss in the turbulent, fast-flowing streams that this species inhabits, allowing tailed frogs to use internal fertilization instead of the external fertilization seen in other frogs. Ascaphidae and Leiopelmatidae are primitive compared to almost all other frogs, as adult individuals retain nine amphicoelous vertebrae and the caudalipuboischiotibialis tail-wagging muscle. Amphicoelous vertebrae are a type mostly found in fish and fossils of early terrestrial tetrapods, such as fossil salamanders and fossil frogs. The joints of these vertebrae allow for significant lateral movement of the vertebral column, a movement most clearly seen when fish use their tails to generate propulsive force. Another ancestral trait (plesiomorphy) in this species is the presence of free ribs in adults, a characteristic only found in the basal archaeobatrachia group. Tailed frogs cannot vocalize, and are small, reaching around 2.5 to 5.0 cm (0.98 to 1.97 in) in total length. They inhabit steep, fast-flowing streams across the northwestern United States (Montana, Idaho, Washington, Oregon, and northern California) and southern British Columbia in Canada, with Rocky Mountain Tailed Frogs found inland and Coastal Tailed Frogs found along coastal British Columbia. A unique trait of tailed frogs is their ability to secrete a group of antimicrobial peptides called ascaphins through their skin. These peptides share very few genetic characteristics with other antimicrobial peptides produced by frogs, but show some similarities to antibacterial peptides found in two species of African scorpion: Pandinus imperator and Opistophthalmus carinatus. Ascaphins are essential for fighting bacteria such as E. coli and S. aureus. The natural habitat of the tailed frog is cold, fast-moving streams with cobblestone bottoms. Tailed frogs are mostly aquatic, but adults can emerge onto land to forage during cool, wet conditions. Their breeding season runs from May through September. Females lay their eggs in strings attached under rocks in fast-moving streams. Larvae take one to four years to complete metamorphosis in these cool, fast-flowing mountain streams. The proportions of cobbles and fine particles (sand and similarly sized fine sediment) in streams are reliable indicators of tadpole abundance: tadpole numbers are inversely proportional to the concentration of fine particles, and directly proportional to the concentration of cobbles. Adult tailed frogs have an exceptionally low thermal tolerance compared to other North American frogs. Eggs are rarely found in waters warmer than 20 °C, and both adults and larvae regularly move between microhabitats to reach water temperatures below 20 °C whenever possible. Tailed frogs prefer temperatures of 16 °C or lower, and eggs develop best when temperatures are between 5 °C and 13.5 °C. Because of this very narrow thermal tolerance, adult frogs may display philopatry (site fidelity) to areas with stable, low temperatures. It has also been hypothesized that tailed frogs may migrate to colder waters during autumn. However, the movements and migratory habits of Ascaphus truei are not well documented, so no confident, conclusive statements can be made about either migratory behavior or philopatry. Adult tailed frogs forage primarily on land along stream banks, but occasionally feed underwater as well. They consume a wide variety of prey, including aquatic and terrestrial insect larvae and adults, other arthropods (especially spiders), and snails. Tadpoles eat small amounts of filamentous green algae and desmids, and consume large quantities of conifer pollen seasonally. During the day, adults take cover under submerged substrates within the stream, or occasionally under similar surface objects located close to the stream. Individuals have also been found in crevices in spray-drenched cliff walls near waterfalls. During winter, tailed frogs are less active, especially in inland populations, and appear to retreat beneath large logs and boulders. Tadpoles require cool streams with smooth-surfaced stones that have a minimum diameter of 55 mm (2.2 in). Tadpoles spend most of their time attached to these substrates using a large oral sucker. The large, sucker-like mouthparts of tadpoles are a second distinctive feature of this species, allowing tadpoles to survive in turbulent water that cannot support other frog species. Tadpoles prefer fully turbulent water over smooth, swiftly flowing water.
