Ascaphus truei Stejneger, 1899
Pacific Tailed Frog, Coastal Tailed Frog, Western Tailed Frog
|Species Description: Stejneger, L. 1899. Description of a new genus and species of discoglossoid toad from North America. Proceedings of the United States National Museum 21: 899.901.|
© 2011 Rob Schell (1 of 99)
Ascaphus truei Stejneger, 1899
Michael J. Adams1
1. Historical versus Current Distribution. Tailed frogs (Ascaphus truei) have been present in the Pacific Northwest for millions of years (since the late Cretaceous; Metter and Pauken, 1969). They may have once had a nearly continuous distribution, but since the late Miocene or early Pliocene their range has been shrinking due to geological events including lava flows, mountain uplifting, and glaciation (Metter and Pauken, 1969; Nielson et al., 2001). Tailed frogs, including the recently recognized A. montanus (see Nielson et al., 2001 and account, this volume) currently inhabit the Cascade Mountains of British Columbia (Ricker and Logier, 1935; Dupuis et al., 2000), Washington (Van Winkle, 1922; Svihla, 1933; Svihla and Svihla, 1933; Visalli and Leonard, 1994), and Oregon (Fitch, 1936; Metter, 1967; Smith, 1997), the Coast Range of British Columbia north to the Noss River (Carl, 1945; Dupuis et al., 2000), the Olympic Mountains (Gaige, 1920; Noble and Putnam, 1931), the Willipa Hills (Adams and Wilson, 1993; Manlow, 1994), the Oregon Coast Range (Metter, 1967; Bury et al., 1991a), and northern California south along the coast to Mendocino County (Myers, 1931a, 1943; Shapovalov, 1937; Salt, 1952; Bury, 1968; Welsh, 1985) and east to Shasta County (Simons and Simons, 1998). Inland, tailed frogs (now recognized as A. montanus; see Nielson et al., 2001; A. montanus account, this volume) occur in the Blue Mountains of southeast Washington (Metter, 1964a), the Wallowa Mountains of northeast Oregon (Ferguson, 1952; Bull and Carter, 1996), central Idaho and the panhandle (Linsdale, 1933a; Corbit, 1960; Maughan et al., 1980), and western Montana (Smith, 1932; Franz and Lee, 1970), including at least one population on the eastern slope of the Rocky Mountains (Donaldson, 1934). Tailed frogs occur from sea level to near timberline: 1,600 m on Mount Rainier; 2,100 m in the Wallowa Mountains (Nussbaum et al., 1983; Leonard et al., 1993). The distribution of tailed frogs does not appear to have changed drastically in the past 100 yr. They are recovering rapidly from extirpations that occurred in the Mt. St. Helens' blast zone (Hawkins et al., 1988).
2. Historical versus Current Abundance. No change documented. In general, sedimentation and warm water temperatures are associated with lower abundances (see "Conservation" below), but there is no published evidence of broad scale decline in this species.
3. Life History Features.
A. Breeding. Reproduction is aquatic.
i. Breeding migrations. None reported. Adults breed in streams they inhabit. Amplexus has been reported from May–October (Gaige, 1920; Noble and Putnam, 1931; Slater, 1931; Metter, 1964b; Wernz, 1969), but Nussbaum et al. (1983) suggest that most breeding occurs in the fall. Females retain sperm in oviductal sperm storage tubules (Metter, 1964b; Sever et al., 2001), and oviposition does not occur until the following spring or summer after spring runoff (Gaige, 1920; Franz, 1970; H.A. Brown, 1975a; Daugherty and Sheldon, 1982a; Adams, 1993; Karraker and Beyersdorf, 1997). Females appear to breed every other year in inland populations, however, smaller clutch sizes suggest that coastal females may breed every year (Metter, 1964b).
ii. Breeding habitat. Breeding and oviposition occur in the streams occupied by adults.
i. Egg deposition sites. Eggs are deposited in strings under large rocks (Gaige, 1920; Metter, 1964a; Franz, 1970; H.A. Brown, 1975a; Adams, 1993; Karraker and Beyersdorf, 1997).
ii. Clutch size. Egg numbers are low (28–96), with coastal populations having fewer (Noble and Putnam, 1931; Metter, 1964a; Franz, 1970; Bury et al., 2001) but larger (3.7–4.5 mm diameter; Metter, 1964a; H.A. Brown, 1989a) eggs. Eggs take about 3–6 wk to hatch (Franz, 1970; H.A. Brown, 1989a). Embryos from the North Cascades of Washington hatched after 28 d in the laboratory at 11 ˚C (H.A. Brown, 1989a). Belton and Owczarzak (1968) describe the pre-ovulatory deposition and storage of hepatic lipids. Wernz and Storm (1969) provide a staging table for embryos.
i. Length of larval stage. Tadpoles hatch from August–September (Metter, 1964a; Franz, 1970; Adams, 1993) and always overwinter at least once. Hatchlings are unpigmented, 13–15 mm total length, and do not fully absorb yolk until they reach 20–21 mm TL (Metter, 1964a; H.A. Brown, 1989a). They reach metamorphosis after 1–2 yr in coastal areas (Wallace and Diller, 1998; Bury and Adams, 1999), usually after 2–3 yr in the Cascades (Metter, 1967) and after 3 yr in inland regions (Metter, 1967; Daugherty and Sheldon, 1982a; Lohman, 2002). A 4-yr larval period was reported near Mount Baker, Washington (H.A. Brown, 1990). Laboratory behavior of tadpoles was described by Altig and Brodie (1972). Cranial osteology was described by Altig (1969), and variations in cranial ossification was described by Moore and Townsend (2003).
ii. Larval requirements. Tadpoles occupy swift mountain streams with cobble substrates (Gaige, 1920; Metter, 1964a; Bury, 1968; Nussbaum et al., 1983; Leonard et al., 1993; Bull and Carter, 1996; Diller and Wallace, 1999; Adams and Bury, 2002). They adhere to smooth rocks using their large, suctorial mouths (Gradwell, 1971). Tadpoles prefer cold water temperatures and are seldom found in streams > 16 ˚C (de Vlaming and Bury, 1970; Claussen, 1973; Welsh, 1990). A strong association with consolidated surface lithologies has been documented in harvested forests (Diller and Wallace, 1999; Dupuis et al., 2000; Wilkins and Peterson, 2000), which may be due partially to a greater sensitivity of streams with sedimentary substrates to logging (Adams and Bury, 2002; Welsh and Lind, 2002). Because of their long larval period, tadpoles typically require permanent water, but some populations with 1-yr larval periods may persist in streams that occasionally dry (Wallace and Diller, 1998; Waters et al., 2001). Sedimentation appears to degrade habitat quality (Noble and Putnam, 1931; Bury and Corn, 1988b; Corn and Bury, 1989a; Welsh and Ollivier, 1998; Dupuis and Steventon, 1999). Severe floods that scour stream bottoms can remove entire tadpole populations (Metter, 1968; Lohman, 2002).
a. Food. Mostly diatoms (Metter, 1964a); some filamentous algae and desmids found in guts. Conifer pollen is seasonally abundant in guts. Fine sand grains are also ingested (Metter, 1964a). Noble (1927) felt that tadpoles ingest most of their food through the external nares. However, Altig and Brodie (1972) found that more food is scraped from rocks and orally ingested. Tadpoles will sometimes crawl up rocks out of the water, possibly to feed (Noble and Putnam, 1931). Altig and Kelly (1974) suggest that the relatively short gut length of tailed frogs may be due to cold water temperatures and slow passage times rather than a carnivorous feeding habit. Addition of phosphate to streams can increase periphyton abundance and coastal tailed frog tadpole growth rate, suggesting nutrient limitation (Kiffney and Richardson, 2001).
b. Cover. Tadpoles use interstices for cover during daylight and emerge to the surface of stones at night (Metter, 1964a; Feminella and Hawkins, 1994). Tadpoles will increase cover use in the presence of non-visual cues from predators (Feminella and Hawkins, 1994).
iii. Larval polymorphisms. Albinism was reported by Pearl et al. (2002). The white on the tip of the tail is absent in Blue Mountain populations (Metter, 1967).
iv. Features of metamorphosis. Metamorphosis (from front-limb emergence to tail resorption) occurs in late summer and lasts approximately 1 mo, although the tail may not be completely resorbed for months (H.A. Brown, 1990; Bury and Adams, 1999).
v. Post-metamorphic migrations. Adults and juveniles are highly philopatric in Montana (Daugherty and Sheldon, 1982b), but movements directly after metamorphosis have not been well documented. Bury and Corn (1987, 1988b) captured numerous recently transformed animals in pitfall traps set in forested stands. These captures suggest a pattern of fall dispersal by recently transformed animals.
D. Juvenile Habitat. Same as adults.
E. Adult Habitat. Adults are aquatic, occupying the streams needed by their eggs and tadpoles. Adults may use thermal microhabitats to avoid warm water temperatures (Adams and Frissell, 2001). After heavy rains or dews, adults may be found in moist woods (Nussbaum et al., 1983; Welsh and Reynolds, 1986). Upland captures of tailed frogs can be common during the autumn and spring (Bury and Corn, 1988a; Gomez and Anthony, 1996).
F. Home Range Size. Marked adults in Montana seldom moved > 10 m upstream or downstream (Daugherty and Sheldon, 1982b).
G. Territories. Not reported.
H. Aestivation/Avoiding Dessication. These behaviors have not been reported.
I. Seasonal Migrations. Daugherty and Sheldon (1982b) report none. Metter (1964a) suggests adults may move up into smaller, more shaded streams during the summer, although Landreth and Ferguson (1967) question this conclusion. Adams and Frissell (2001) reported seasonal movements of adults consistent with an avoidance of warm water temperatures. Wahbe and Bunnell (2001) describe movement of tadpoles in streams flowing through harvested and natural forests in southwestern British Columbia.
J. Torpor (Hibernation). Not reported.
K. Interspecific Associations/Exclusions. Frequently occupy small streams with giant salamanders (Dicamptodon spp.) and torrent salamanders (Rhyacotriton spp.), although each species is associated with somewhat different microhabitats (Metter, 1964a; Bury et al., 1991b; Welsh and Ollivier, 1998; Adams and Bury, 2002). Fish can be predators (Feminella and Hawkins, 1994); Noble and Putnam (1931) suggest that salmonids may exclude tailed frogs, but tailed frogs have been found coexisting with a variety of fish including salmonids (Metter, 1964a; Feminella and Hawkins, 1994).
L. Age/Size at Reproductive Maturity. Tailed frogs are remarkable among anurans in their delayed maturity. In a Montana study, reproductive maturity was reached in yr 7 (4 yr after metamorphosis), but most males did not breed until yr 8 and most females did not breed until yr 9 (Daugherty and Sheldon, 1982a). Mature males were > 34 mm (snout to base of “tail”) and mature females were > 44 mm.
M. Longevity. Long lived. Daugherty and Sheldon (1982a) recovered a wild female with a known minimum age of 14 yr. They speculate that females may live 15–20 yr and males somewhat less.
N. Feeding Behavior. Adult tailed frogs appear to be generalist predators, feeding on insects and other invertebrates as they are available (Fitch, 1936; Metter, 1964a; Bury, 1970). They feed along stream banks and adjacent forest at night (Metter, 1964a; Daugherty and Sheldon, 1982b). Nishikawa and Cannatella (1991) describe the kinematics of prey capture. Abourachid and Green (1999) describe swimming behavior.
O. Predators. Known predators include western terrestrial garter snakes (Thamnophis elegans), common garter snakes (T. sirtalis), giant salamanders (Dicamptodon spp.), trout (Salmonidae), sculpins (Cottus confusus), dippers (Cinclus mexicanus), and hellgrammites (Megaloptera; Metter, 1963; Metter, 1964a; Daugherty and Sheldon, 1982a; Feminella and Hawkins, 1994; Jones and Raphael, 1998; Karraker, 2001). Blair and Wassersug (2000) describe predator-induced tail damage.
P. Anti-Predator Mechanisms. Nocturnally active, seek cover under rocks during daylight or in presence of non-visual cues from predators (Feminella and Hawkins, 1994). Adults have been observed to fold their limbs against their body and let the current carry them away when disturbed (Metter, 1964a).
Q. Diseases. None reported.
R. Parasites. The gut ciliate, Protoopalina, is found in tadpoles (Metcalf, 1928; Metter, 1964a). Both larvae and adults can host subcutaneous, encysted parasitic flukes (Anderson, 1964; Metter, 1964a).
4. Conservation. Population densities vary considerably (Lohman, 2002), but lower abundances have been documented following timber harvest (Gaige, 1920; Noble and Putnam, 1931; Metter, 1964a; Bury and Corn, 1988b; Corn and Bury, 1989a; Bury et al., 1991b; Bull and Carter, 1996; Aubry, 2000) and road construction (Welsh and Ollivier, 1998). Tailed frogs have been characterized as both environmentally sensitive and resilient to large scale disturbance. They were one of the first vertebrates to recover following the 1980 eruption of Mt. St. Helens (Hawkins et al., 1988; Crisafulli and Hawkins, 1998). While Metter (1964a) reported long-term absence of a tailed frog population following timber harvest, some populations persist in forests with extensive timber extraction (Diller and Wallace, 1999; Dupuis et al., 2000; Wilkins and Peterson, 2000). Riparian buffers may help protect populations from timber harvest impacts (Dupuis and Steventon, 1999). In general, sedimentation and warm water temperatures are associated with lower abundances (Bury and Corn, 1988b; Hawkins et al., 1988; Corn and Bury, 1989a; Welsh and Ollivier, 1998; Diller and Wallace, 1999), but there is no published evidence of broad scale decline in this species.
1 Michael J. Adams
2 Christopher A. Pearl
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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