Ambystoma gracile adults may be either metamorphosed terrestrial salamanders or neotenic water-dwellers.
Metamorphosed adults measure 14-22 cm in total length (Boundy and Balgooyen 1988). They are
dark brown, gray, or black above and a lighter brown below.
A glandular ridge forms a rounded top edge on the tail; the lower edge of the
tail is sharp (Petranka 1998; Snyder 1963). Conspicuous oval parotoid glands
sit immediately behind the
eyes. The tail ridge appears rough due to concentrations of granular glands
(Brodie and Gibson 1969). Both the parotoid and tail ridge glandular areas are pitted with openings of poison glands.
Broad head, relatively small eyes. No tubercles on the underside of the feet (Stebbins 1985).
Sometimes terrestrial individuals have small, irregular, whitish or yellowish spots and
blotches on their dorsum (see Comments section below).
Neotenic adults are strictly aquatic and retain gills. They may grow as
large as 13 cm in snout-vent length and 26 cm in total length
(Boundy and Balgooyen 1988).
They are brownish to olive green in color, mottled with yellow and black. Distinct yellow spots sometimes sometimes dot the sides and tail.
Ventral color varies from cream to pale or dark gray (Petranka 1998).
The parotoid glands of untransformed adults are less prominent than those of
transformed adults (Licht and Sever 1993).
Both terrestrial and neotenic males become darker than females during the breeding season.
Unmetamorphosed adult males have hypertrophied hindlimbs and feet, are less
spotted, and have an enlarged glandular ridge on the tail (Snyder 1956).
Larvae belong to the pond type, having long gills, long toes, and a long dorsal
fin (Stebbins 1985). Hatchlings average about 8 mm in snout-vent length
(Licht 1975). They have
concentrated dark pigment along the base of the dorsal fin.
Older larvae vary in color from dark brown to olive green or light yellow.
They often have sooty blotches on the dorsum and may have yellow flecks or spots
along the sides (Stebbins 1985).
Distribution and Habitat
Country distribution from AmphibiaWeb's database: Canada, United States
U.S. state distribution from AmphibiaWeb's database: Alaska, California, Oregon, Washington
Canadian province distribution from AmphibiaWeb's database: British Columbia
Inhabits the northwest Pacific coast of North America. Found from southeastern
Alaska on May
Island south to the mouth of the Gualala River, Sonoma County, California. Occurs
from sea level to timberline, but
not east of the Cascade Divide. Range includes Vancouver Island in British
Columbia and Cypress, Whidbey,
Bainbridge, and Vashon Islands in Washington (Snyder 1963).
The spotted forms
occur in the northern portion of A.
gracile's range (Petranka 1998; Snyder 1963; see Comments section below).
Populations with neotenic adults are
widespread, but the frequency of gilled
adults increases with altitude such that adults at low and intermediate
altitudes are almost all terrestrial, while adults at
very high elevations are mostly neotenic (Eagleson 1976).
adults live in mesic habitats ranging from
grasslands to mesophytic forests. Terrestrial adults are mostly fossorial,
and are usually active on the surface only during fall rains and spring
migrations to their
aquatic breeding sites. However, they can sometimes be found under logs and
other surface debris outside of the breeding
season (Petranka 1998; Efford and Mathias 1969).
Life History, Abundance, Activity, and Special Behaviors
Terrestrial adults may defend themselves vigorously. When threatened, they may
close their eyes, assume a head-butting position, and elevate the tail. They
secrete a sticky white poison from glands on the head, back, and tail, using head-butts and and tail-lashes to smear the poison onto the attacker
(Stebbins 1985; Licht and Sever 1993). A ticking sound may accompany this defense
Larvae and neotenic adults flee attack from natural predators such as trout and beetle larvae (Nussbaum et al. 1983).
This species breeds in permanent or semi-permanent waters, ranging from small, shallow ponds
to large, deep lakes, and sometimes including side pools of slow streams. Breeding
takes place in the spring; the exact timing varies with latitude and
elevation (Brown 1976; Licht 1969; Licht 1975).
Mating pairs of A. gracile enact an elaborate courtship ritual that seems to
vary between different regions. Fertilization is internal; the
female picks up a spermatophore deposited by the male (Licht 1969; Knudsen 1960).
Length of embryonic development is positively correlated with water temperature
and varies from 2-9 weeks (Petranka 1998). Most larvae in lowland
populations transform when 12-14 months old, in the spring following hatching
(Eagleson 1976; Licht 1975). Larvae at high elevations transform in
their third year (Eagleson 1976).
Hatchlings feed on zooplankton; older larvae eat a variety of prey, including
annelids, mollusks, insect larvae, copepods, ostracods, and flatworms
(Licht 1975; Efford and Tsumura 1973).
Trends and Threats
The status of Ambystoma gracile populations is unknown (Blaustein et al. 1994).
No declines are apparent in Canada (Weller and Green 1997). In the
Cascade Mountains of Washington, Aubry and Hall (1991) found A. gracile to
be far less abundant in young forests than in old-growth forests.
and Bury (1991) surveyed Western Oregon and found little correlation between salamander abundance and stand age, so it remains
unclear whether A. gracile requires old growth forest to thrive.
Clear-cutting, however, seems to
render the habitat unsuitable; Corn and Bury found no salamanders on recent clear-cuts.
Petranka (1998) suggests leaving a forest buffer of 200-250 m surrounding breeding sites used by terrestrial adults
to preserve optimal environmental conditions for local populations.
At an elevation of 183 m in the Cascade Mountains of Oregon, Blaustein et al. (1995) found A. gracile embryos to hatch with less mortality when shielded from
UV-B radiation than when allowed to develop exposed to direct sunlight.
This experiment was conducted in pond water 5-10 cm deep, which they claim is a common
oviposition site for A. gracile in the Oregon Cascades.
often lay their eggs at greater depths and often in murky water, where they
would be protected from UV-B,
so the ecological relevance of Blaustein et al.'s experiment is controversial. Whether UV-B actually harms A. gracile populations is unknown
Because A. gracile breeds in relatively permanent bodies of water, Canadian populations may be unaffected by the increase in aridity predicted to occur in Canada due to
global warming. However, decreased survival due to
drying of breeding habitat may
A. gracile populations may be negatively affected by introduced predatory fish,
such as trout and char.
These fish can reduce or eliminate montane populations of
ambystomatid salamanders (Burger 1950; Blair 1951; Sprules 1974; Taylor 1983).
Tyler et al. (1998) tested the effects of trout on larvae of
and A. macrodactylum in artificial ponds and found that trout reduced both
survivorship and average snout-vent length, and also narrowed the range of habitat use for larvae of both species. Trout also reduced average body mass of A. gracile larvae.
Relation to Humans
The poison secreted by terrestrial Northwestern Salamanders may
irritate the skin of
some people (Stebbins 1985).
No morphological differences have been found to distinguish neotenic
larvae from those that will transform (Snyder 1963).
The spotted and unspotted varieties
were originally designated as separate subspecies, with Ambystoma
gracile decorticatum (British Columbia Salamander) possessing spots and
Ambystoma gracile gracile
(Brown Salamander) lacking spots. The spotted form occurs in the northern part of the range for A. gracile. A dividing line of 51 degrees north
latitude was recognized
between the two subspecies, with
A. g. decorticatum occurring north of the line and A. g. gracile
living to the south (Snyder 1963). Morphological characters such as the presence of 3 instead of 4 phalanges on
the fourth toe, more prominent parotoid glands, and rows of 4 rather than 2 teeth on the prevomers
have been used to differentiate between the unspotted
A. g. gracile and the spotted A. g. decorticatum (Dunn 1944). However, Titus (1991) found that these distinctions do not always hold true and that genetic variation
does not always correlate well with subspecies, and he suggested
that A. gracile should not be split into subspecies.
The specific epithet gracile is derived from the Latin term gracilis which means "slender" or "delicate." The subspecific name decorticatum is
taken from the Latin de ("from") and cortex ("bark" or "cork"), meaning "like bark"
See another account at californiaherps.com.
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Written by John Romansic (romansic AT uclink4.berkeley.edu), UC Berkeley
First submitted 1999-04-13
Edited by Kellie Whittaker (2008-09-21)
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