Ascaphus truei
Coastal Tailed Frog
(Also: Tailed Frog)

Tailed frogs, Ascaphus truei, occur from northwestern California north to the Portland Canal and Nass River of British Columbia. This range is bordered by the Cascade Mountains to the east and the Pacific coast to the west. Several separate populations are also found in the Blue Mountains of southeastern Washington and northeastern Oregon as well as in the northern Rocky Mountains of northern Idaho and western Montana. (Stebbins, 2003; Adams and Pearl, 2005; Leonard, et al., 1993; Mallory, 2004; Stebbins, 2003)

Ascaphus truei prefers clear, cold streams of mountainous regions with step-pools, such that the slope is neither too shallow nor too steep. These frogs inhabit a wide range of elevations from coastal to mountainous. Stream temperatures must remain cool even in summer months, as this species is known to have narrow temperature tolerances. Also, coarse substrates are favored for egg-laying and over-wintering events. As larvae do exhibit a long developmental period, stream habitats must be permanent features of the landscape. Juveniles and adults, however, further require the presence of a mature or old growth forest alongside their stream habitat. While A. truei will not venture too far from the water, juveniles and adults will utilize riparian vegetation for food and refuge. This vegetation is also important to larvae, as it helps to control stream temperatures and prevent excessive sedimentation through bank stabilization. (Adams and Pearl, 2005; Mallory, 2004; Metter, 1964; Wallace and Diller, 1998)

Since Ascaphus truei spends its life in association with fast-flowing streams, it has evolved some morphological adaptations that stand out from other frogs and toads. For example, the lungs are greatly reduced, presumably to control buoyancy, and the toe tips are hard and keratinized, to facilitate crawling among rocks on the stream bottom.

Juvenile and adult stages of A. truei are small in size, typically ranging from 2.2 to 5.1 cm in snout-vent length. Overall, color is usually comparable to the tailed frog’s substrate and may vary from tan to chocolate brown or olive green. Regardless of the color, its skin has a characteristic rough feel. Moreover, the head is comparatively large and flattened with a light triangular-shaped mark generally present between the snout and eyes. The eyes themselves have visibly vertical pupils, and a dark stripe extends from the snout to the shoulder. Some more obvious adaptations to its streamside habitat include a slight webbing of the toes, with the outer hind toes also flattened. In addition, A. truei lacks tympani or ear membranes and, as a result, lacks the capacity to communicate acoustically, a likely adaptation to the steady sound of flowing water. Tailed frogs get their common name from another aquatic adaptation: males have a short, tail-like copulatory organ used during internal fertilization. Tailed frogs exhibit additional sexual dimorphism in that males are smaller than females, and they develop black, horny pads on the insides of their thighs during the mating season to aid gripping females during amplexus.

While tadpoles of A. truei average little more than 11 mm after hatching, they may grow to 65 mm in length before metamorphosis. Initially, hatchlings have no color, but are instead identified according to the presence of a prominent yolk sac seen in the abdomen. However, tadpoles eventually take on a black to brownish-grey coloration of the body that is covered with black speckling. A white dot discernible on the tip of the tail and an obvious copper-colored bar between the eyes and snout are additional field marks for identification. Tailed frog tadpoles also have some adaptations to keep from being swept away by stream currents. The body is flattened ventrally and the tail is laterally compressed. Moreover, the mouth has evolved into an oral disc that is sucker-like, allowing for attachment to rocks.

The eggs of A. truei are unpigmented and are laid in a gelatinous string beneath a rock in shallow water. (Adams and Pearl, 2005; Leonard, et al., 1993; Metter, 1964; Stebbins, 2003)

While most frogs and toads exhibit external fertilization, Ascaphus truei is unique in that it has internal fertilization. Female tailed frogs purposefully attach their eggs to the bottom of big rocks or boulders found submerged in the stream. Hatching occurs about six weeks after deposition of the eggs. Tadpoles utilize their large yolk sac for nourishment throughout the winter months, after which development of a suctorial mouth allows them to prey upon other organisms. Following one to four years, metamorphosis takes place, producing juvenile tailed frogs that differ dramatically in appearance from their previous larval form. Metamorphosis can last up to 60 days. The age that juveniles reach sexual maturity varies geographically, with coastal populations maturing at 2 to 3 years old and montane populations maturing at 8 to 9 years old. (Adams and Pearl, 2005; Leonard, et al., 1993; Mallory, 2004; Stephenson and Verrell, 2003; Wallace and Diller, 1998)

Tailed frogs are unique among the anurans in exhibiting a combination of amplexus and copulation during courtship and mating. Courtship occurs at the onset of fall, between September and October, and is carried out in the water. During courtship, a male typically lunges or swims suddenly toward a female of the same species. Clasping the female’s body directly anterior to her pelvic region, the male may then perform either inguinal or ventral amplexus. Once in the proper position, copulation can follow, the male's erect “tail” inserted into the female’s cloaca. To press closer to the female during copulation, the male may repeatedly produce thrusts of his pelvic region, his “tail” still within the cloaca. (Adams and Pearl, 2005; Leonard, et al., 1993; Mallory, 2004; Stephenson and Verrell, 2003; Wallace and Diller, 1998)

Tailed frog females have been shown to reproduce biennially, while males may mate annually. This behavior may vary geographically. Although courtship and mating occur in the fall, tailed frog females store the sperm and do not deposit eggs until June or July. When deposition finally takes places, a dual strand of 44 to 85 small-sized eggs is fixed to the base of a rock or boulder within the stream system. After approximately six weeks, hatchlings then appear. The tadpole or larval stage may last anywhere from one to four years, geographic location likely impacts the length. Coastal populations spend 1 to 3 years in the larval state, whereas montane or inland populations spend 3 to 4 years. Tailed frog tadpoles undergo metamorphosis, which includes absorbing their tails, developing an adult mouth, losing the suction mouth, and developing legs. A juvenile may not reach reproductive maturity until it is 2 to 8 years old, varying geographically. (Adams and Pearl, 2005; Leonard, et al., 1993; Mallory, 2004; Stephenson and Verrell, 2003; Wallace and Diller, 1998)

There is little available information on parental care in Ascaphus truei.

With a maximum lifespan of at least fourteen years, and from 2 to 9 years required to attain sexual maturity, Ascaphus truei has one of the longer life histories known among anurans. (Adams and Pearl, 2005; Daugherty and Sheldon, 1982)

Juvenile and adult tailed frogs are often active nocturnally, foraging for food under the cover of night. Although they typically stay close to the streamside, juveniles and adults may move a modest distance into the neighboring mature or old growth forests. Tadpoles, on the other hand, may display either nocturnal or diurnal behavior, the choice of when to forage for food likely dependent on the presence or absence of certain predatory species. Moreover, tadpoles differ in that they are largely sedentary within the stream system. Activity dramatically decreases during winter, though they do not hibernate, and some individuals remain active. (Adams and Pearl, 2005; Leonard, et al., 1993; Mallory, 2004; Metter, 1964)

Territory size is unknown for Ascaphus truei.

Communication through calls, as characteristic of most anurans, does not appear possible due to the absence of the tongue, vocal sacs, middle and external ear bones, and external eardrums which are critical to creating and perceiving sound. With acoustic communication lacking in Ascaphus truei, this species is presumably reliant on visual and tactile cues to carry out courtship and mating activities. Still, more research is needed in this subject of study, as chemical cues may prove important to communication as well. (Adams and Pearl, 2005; Hallock and McAllister, 2005; Leonard, et al., 1993; Stephenson and Verrell, 2003; Vitt and Caldwell, 2009)

Tadpoles of Ascaphus truei primarily eat diatoms scraped off from underwater rocks. Conifer pollen and filamentous algae may also be incorporated into their diet. Post-metamorphic juveniles and adults, on the other hand, will forage for various insects and terrestrial arthropods alongside their stream habitat or in adjacent riparian vegetation. Spiders, ticks, mites, and snow fleas are all potential prey. Snails are an additional prey species for A. truei juveniles and adults. However, because it lacks a tongue attached at the front of its mouth, tailed frogs do not have the ability to flip their tongue out to take prey, a trait seen in most other anurans. (Adams and Pearl, 2005; Leonard, et al., 1993; Mallory, 2004)

Little is known regarding potential predators of Ascaphus truei, as observations regarding this subject of study are few in number. Of those accounts that exist, common garter snakes, shrews (Sorex genus) and Western terrestrial garter snakes were observed consuming post-metamorphic tailed frogs. There are also accounts of hellgrammites (Order Megaloptera), larval Cope’s giant salamanders and Pacific giant salamanders consuming larval tailed frogs. Other predators include trout (Family Salmonidae), sculpins and dippers. (Adams and Pearl, 2005; Leonard, et al., 1993; Lund, et al., 2008)

Tailed frog tadpoles can actually act as the dominant herbivore in some stream habitats. However, Ascaphus truei is restricted to aquatic lotic systems as a tadpole. As a juvenile or adult on the other hand, A. truei may play an active part in both its aquatic and adjacent terrestrial ecosystem through interaction with its prey and predators. (Mallory, 2004)

Due to the sensitivity of Ascaphus truei to alterations of its habitat, this stream-dwelling species may serve as an indicator species in assessing ecosystem health. (Adams, 1993)

There are no known negative impacts of Ascaphus truei on humans.

Ascaphus truei is ranked as a species of “Least Concern” on the IUCN list and a “Species of Concern” for the Pacific region on the United States Fish and Wildlife Endangered Species List. The reason behind its status on either list is the fact that A. truei may be impacted by logging and construction activities. These practices can negatively alter tailed frogs' habitats by causing stream temperatures to rise and siltation to occur. (Adams and Pearl, 2005; Hammerson and Adams, 2010; "Tailed frog (Ascaphus truei)", 2010)