Ambystoma jeffersonianum (Green, 1827)
1. Historical versus Current Distribution. Because of the difficulty of
distinguishing Jefferson salamanders (Ambystoma jeffersonianum) from
those of unisexual Ambystoma populations of hybrid origin, the status of
Jefferson salamanders is uncertain and their ecology poorly understood throughout much of
their range. Early studies (prior to the mid 1960s) need to be viewed with caution
because many may include blue-spotted salamanders (A. laterale) or
unisexual populations. Jefferson salamanders are distributed in the United States
from eastern Illinois and south-central Kentucky northeast to northern Virginia and
southwestern New England (Petranka, 1998). There is no evidence to indicate that
current distributions differ from historical distributions, but populations have been
lost due to habitat destruction, alteration, and acidification (Sadinski and Dunson,
1992; Rowe and Dunson, 1993).
2. Historical versus Current Abundance. The relative abundance of Jefferson
salamanders is uncertain because they often coexist with unisexual Ambystoma
hybrids. Recent studies indicate that unisexual populations have a larger range
than previously thought (Rye et al., 1997) and often outnumber Jefferson salamanders when
they are syntopic (Uzzell, 1964; Nyman et al., 1988; Bogart and Klemens, 1997;
unpublished data). Jefferson salamanders are considered Locally Common–Rare
in New England (DeGraaf and Rudis, 1983) and are on the Special Concern list in Vermont,
Massachusetts, and Connecticut (Hunter et al., 1999). They are only known from two
counties in eastern Illinois (Phillips, 1991) and have recently been listed as state
Threatened. The relative abundance of Jefferson salamanders in Indiana is
considered occasional (Simon et al., 1992) or uncommon (unpublished data).
Long-term studies from Indiana (S. Cortwright, personal communication) and Ohio (Brodman,
1995, 2002) indicate that some populations are stable. From 1989–'95 there
were 36 new township records of Jefferson salamanders in Ohio. In Pennsylvania,
the total number of eggs that females deposit is positively correlated with pH levels and
negatively correlated with aluminum levels (Rowe and Dunson, 1993; see also Petranka,
1998). At a pH of < 4.5, eggs and larvae will perish. Given that over half
of the ponds studied in a region of Pennsylvania had a pH of ≤ 4.5, the abundance of
Jefferson salamanders is likely much lower than it was historically. Of the
specimens examined from 106 sites in New York and New England, 70% are unisexual hybrids
and most of the rest (23%) are blue-spotted salamanders (Bogart and Klemens, 1997).
Fewer than 7% of the specimens collected were Jefferson salamanders and < 3% of the
sites contain Jefferson salamander populations that were not syntopic with unisexual
populations (Bogart and Klemens, 1997). Jefferson salamanders are common in the
western panhandle of Maryland (Thompson et al., 1980; Thompson and Gates, 1982).
Little is known about the relative abundance of southern populations in Kentucky, West
Virginia, and Virginia.
3. Life History Features.
Reproduction is aquatic.
i. Breeding migrations. Jefferson salamanders are among the first amphibians to
breed and are the earliest Ambystoma species to breed, with the exception of the
fall-breeding marbled salamanders (Ambystoma opacum; Brodman, 1995;
Petranka, 1998, Minton, 2001). Jefferson salamanders breed as early as
December–January in southern Indiana (P.K. Williams, 1973; Minton, 2001) and
Kentucky (Smith, 1983) or as late as March in northern Ohio (Downs, 1989a; Brodman, 1995)
and Pennsylvania (Mohr, 1931). They migrate from upland overwintering sites to
wetland breeding sites. Males typically migrate first and will move while the
ground remains frozen (Bishop, 1941a, 1943; Douglas, 1979; Douglas and Monroe, 1981;
Downs, 1989a,b; Brodman, 1995; see Petranka, 1998). Warm nighttime rains or heavy
snowmelts typically trigger spring breeding migrations; adults will migrate during the
day under overcast skies (Bishop, 1941a). Adults breed early enough in the season
that they can be caught out and killed by cold snaps (Petranka, 1998). Adults in
southern populations occasionally will migrate to breeding wetlands in autumn, where they
overwinter (Douglas and Monroe, 1981; Petranka, 1998).
Breeding in northern
populations tends to occur in single bouts that usually last only a few days while
southern populations breed in several bouts interrupted by cold weather (Bishop, 1941a;
Douglas, 1979; Brodman, 1995). Sex ratios of males:females at any one time are
usually greater than 3:1, with males staying for 16–30 d and females for
19–21 d (Collins, 1965; Downs, 1989b; Petranka, 1998). In some populations
males breed annually while females skip ≥ 1 yr before returning to breed (P.K.
Williams, 1973; Petranka, 1998).
adults migrate from wetlands back to underground retreats in the forest floor.
Douglas and Monroe (1981) show that it takes about 45 d to move ≥ 250 m to these
sites. Jefferson salamanders have been found between 250–1,600 m from
breeding sites (Bishop, 1941a; P.K. Williams, 1973; Downs, 1989b).
are one of four species that participate in the unisexual Ambystoma complex
present in recently glaciated areas of the northeastern United States. In some
ponds supporting this complex, unisexual female salamanders may outnumber males (Uzzell,
1964; Wilbur, 1971; Nyman et al., 1988; see also Petranka, 1998), and in these ponds
Jefferson salamander females will interfere with amplexing pairs (Bishop, 1941a).
Jefferson salamander males lay fewer spermatophores when courting females of the
unisexual Ambystoma complex than when courting conspecific females (Petranka,
ii. Breeding habitat. Adults typically breed in vernal and semi-permanent woodland
pools but also occasionally in permanent, fishless woodland ponds (Bishop, 1941a; Douglas
and Monroe, 1981; Brodman, 1995). Breeding ponds tend to be isolated from larger
water bodies such as oxbows and lakes and tend to be cooler, more turbid and contain more
aquatic vegetation than ponds that are not used (Thompson et al., 1980).
i. Egg deposition sites. Females begin laying eggs on submerged twigs, tree
branches, and emergent vegetation 1–2 d following mating. Egg masses on firm
supports such as twigs are ovoid; eggs laid on grasses and other vegetation are
scattered. Females preferentially lay their eggs on the thin twigs of fallen
branches and submerged ends of live willow branches (personal observations). Eggs
are 2–2.5 mm in diameter. In time, many egg masses are colonized by symbiotic
green algae Oophila sp. (Gatz, 1973). Average eggs/mass range from
14–31 (Smith, 1911a; Bishop, 1941a; Seibert and Brandon, 1960; Smith, 1983;
ii. Clutch size. Ovarian egg counts vary from 140–280 (Bishop, 1941a; Uzzell,
1964). Egg densities range from 57 eggs/m2 in Ohio (Brodman, 1995) to 123
eggs/m2 in Indiana (Cortwright, 1988) to 469 eggs/m2 in Kentucky (Douglas,
range from 3–14 wk, depending on temperature and latitude (Bishop, 1941a; Smith,
1983; Brodman, 1995). Embryonic survivorship tends to be high (71–96%) when
the pH is ≥ 6.0 (Rowe and Dunson, 1993; Brodman, 1995).
i. Length of larval stage. From 2–4 mo and at sizes ranging from 52–78
mm (Bishop, 1941a; Minton, 1954; Downs, 1989b). Survival is reported to be < 1%
in some populations (Thompson et al., 1980; Downs, 1989b), but can be higher in others
(Pough and Wilson, 1977; Brodman, 1996; S. Cortwright, personal communication).
ii. Larval requirements.
a. Food. Jefferson salamander larvae are opportunistic and size-selective feeders
that are gape-limited because they swallow most prey whole. Larvae take a variety
of prey including ostracods, cladoceran and copepod zooplankton, nematodes, snails, and a
range of aquatic and adult insects including chironomid (Diptera) larvae (Smith and
Petranka, 1987; Petranka, 1998). Larvae are aggressive feeders and will cannibalize
smaller larvae and prey upon spotted salamander (Ambystoma maculatum)
larvae (Brandon, 1961; Smith and Petranka, 1987; Brodman, 1996, 1999b). Smaller
Jefferson salamander larvae are sometimes found with missing limbs, gills, or tails
(Petranka, 1998; personal observations).
b. Cover. Larvae are nocturnal, emerging from vegetation, where they are found
during the day, to feed either on the wetland bottom or to float and feed in the water
column. Nocturnal vertical migration and stratification has been observed in some,
but not all, Jefferson salamander populations (Anderson and Graham, 1967; Brodman,
1995). Jefferson salamander larvae will use leaf litter and algae patches as
refuges in the presence of predatory eastern tiger salamander (Ambystoma
tigrinum) or marbled salamander larvae (Brodman and Jaskula, 2002).
iii. Larval polymorphisms. While cannibalism is known, cannibal morphs (sensu
Powers, 1907) have not been documented. Clanton (1934) and Bishop (1943) noted that
there were dark and light forms in many populations of what was then thought to be
Jefferson salamanders. Minton (1954) clearly distinguished these forms as two
species (Jefferson and blue-spotted salamanders). Uzzell (1963, 1964) later found
that the Jefferson salamanders and blue-spotted salamanders were distinct diploid species
and that there were two sympatric all-female populations that were unisexual hybrids with
triploid chromosome numbers. These unisexual Ambystoma populations
typically use gynogenetic reproduction in which the unisexual females use male
blue-spotted salamanders, Jefferson salamanders, small-mouth salamanders, or tiger
salamanders to stimulate egg laying without the incorporation of male genes in the
progeny (see the unisexual Ambystoma account by Phillips and Mui, this
volume, for an explanation of this phenomenon). Many genomic combinations
of unisexual hybrids are now known between blue-spotted salamanders and Jefferson
salamanders (JLL, JJL, JL, JLLL, LLLL, and JLLLL [with initials denoting the species name
of the parental genetic component as follows: J = jeffersonianum; L = laterale]),
small-mouth salamanders (LT, LLT, LTT, JLT, TTT, JJLT, LLLT, LLTT, and LTTT [T =
texanum]), and tiger salamanders (JLTi, LTTi, and LTTTi [Ti = tigrinum]). Because
of this confusion, little research has been done on the autecology of Jefferson
salamanders. The historical literature can also be confusing. Clanton (1934)
and Wacasey (1961) performed detailed ecological studies on "Jefferson
salamanders" in Michigan. However, the range of the Jefferson salamanders does
not extend into Michigan, so these widely cited studies describing Jefferson salamander
ecology must refer to either blue-spotted salamanders or unisexual hybrids.
iv. Features of metamorphosis. Jefferson salamander larvae grow fast and can
complete development in 2–3 mo. Metamorphosis usually occurs in late July to
early August in northern Ohio, but can occur as early as June if the pond dries (personal
observations). In southern Indiana, larvae have transformed as early as late May
(Minton, 2001), and larvae have been found in ponds as late as November, indicating that
larvae may overwinter in some populations (Cortwright, 1988).
v. Post-metamorphic migrations. Juveniles move a mean of 92 m (range 3–247
m) away from breeding wetlands into floodplain and upland forest floor habitats during
their first 10 d (P.K. Williams, 1973).
vi. Neoteny. Not known to occur.
Habitat. Little is known about the terrestrial ecology of Jefferson salamanders
(Petranka, 1998). In northern populations, juveniles are more active on the forest
floor than are adults or juveniles in more southern populations (Green and Brant, 1966;
Petranka, 1998). Juveniles appear to spend most of their time in burrows, where
they feed on soil invertebrates (Petranka, 1998).
Habitat. Jefferson salamanders are rarely caught above ground outside of breeding
migrations. When encountered, they are typically scattered in deciduous forests
near suitable breeding wetlands (Petranka, 1998). Adults live in burrows,
including rodent burrows (P.K. Williams, 1973; Douglas and Monroe, 1981), and are found
more often in well-drained upland forest sites than are other species of forest-dwelling
Ambystoma (Downs, 1989b; Petranka, 1998).
F. Home Range
Size. Observations of post-breeding adults returning to burrows (Bishop, 1941a;
P.K. Williams, 1973; Douglas and Monroe, 1981) over long distances (250–1,600 m)
suggest that Jefferson salamanders have home ranges that they retain from year to
Aestivation/Avoiding Dessication. Unknown, but individuals likely respond to dry
conditions by going deeper into burrows.
Migrations. Jefferson salamanders migrate to their wetland breeding ponds from the
underground burrows they use for overwintering (Douglas and Monroe, 1981).
Following breeding, 3–4 wk later, they migrate back to feed and grow, often to
their overwintering burrow (P.K. Williams, 1973; see also Faccio, 2003).
Populations in south-central Kentucky have been observed in autumn migrations (Douglas
and Monroe, 1981). Other migrations are unknown, although animals probably move
nearer or farther from the soil surface with increasing or decreasing moisture
(Hibernation). In burrows below the frost line.
Associations/Exclusions. Jefferson salamander populations frequently coexist and
share breeding sites with unisexual Ambystoma hybrid salamanders, marbled
salamanders, spotted salamanders, small-mouthed salamanders, eastern newts
(Notophthalmus viridescens), wood frogs (Rana
sylvatica), and spring peepers (Pseudacris crucifer; Thompson
and Gates, 1982; Cortwright, 1988; Downs, 1989b; Sadinski and Dunson, 1992; Brodman,
1995; personal observations). They can share habitat with spotted salamanders as
often as 40% of the time in some parts of their range (Thompson and Gates, 1982).
In regions of sympatry, Jefferson salamanders and blue-spotted salamanders are not known
to share breeding sites (Anderson and Giacosie, 1967; Nyman et al., 1988; Bogart and
Klemens, 1997). Studies on the interactions among Jefferson salamanders, marbled
salamanders, and spotted salamanders indicate a complex density-dependent set of
interactions among larvae involving both competition and predation, including cannibalism
(Cortwright, 1988; Brodman, 1996, 1999b). The effect on Jefferson salamander
population dynamics of interactions with unisexual Ambystoma populations is
unknown and may be important with regards to the conservation and status of this
L. Age/Size at
Reproductive Maturity. Juveniles mature in 2–3 yr (Bishop, 1941a; P.K.
Williams, 1973) and at SVLs of 62–68 mm for males and 76–78 mm for females
(Uzzell, 1967a; P.K. Williams, 1973).
Jefferson salamanders were not included among the species that have captive longevity
records (Bowler, 1977); no studies using skeletochronology have been conducted.
Mark-recapture studies indicate that 10–18% of marked adults survived for 3 yr
(Collins, 1965; P.K. Williams, 1973).
Behavior. Adults and juveniles are thought to feed on earthworms and other soil
invertebrates (Downs, 1989b; Petranka, 1998).
During breeding migrations, adults are vulnerable to predation from mammals such as
striped skunks (Mephitis mephitis) and raccoons (Procyon
lotor); shrews will feed on adults during other times of the year (Petranka,
1998). Petranka (1998) also suggests owls and woodland snakes will feed on adults
Mechanisms. Adults elevate the pelvis and tail, undulate the tail and coil the body
(Brodie, 1977), and will respond to tongue-flicks from snakes (Dodd, 1977b; Ducey and
Brodie, 1983; Brodie, 1989). The dorsal surface of the tail contains glands that
produce a noxious, adhesive secretion. In tiger salamanders, the noxious component
of this secretion has neurotoxic effects (Hamning et al., 2000). Larvae seek refuge
and reduce activity when in the presence of large tiger salamander larvae (Brodman and
Jaskula, 2002) and adult eastern newts (personal observations).
4. Conservation. The main threats to Jefferson salamanders are habitat
destruction and acidification of breeding ponds. They need undisturbed well-drained
upland forest sites (Downs, 1989; Petranka, 1998) that are within 200–250 m of
seasonal, semi-permanent, and fish-free permanent wetlands (Bishop, 1941; Douglas and
Monroe, 1981; Semlitsch, 1998) that are not acidic (Sadinski and Dunson, 1992; Rowe and
Dunson, 1993). Because unisexual Ambystoma hybrids often outnumber
Jefferson salamanders when they are syntopic (Uzzell, 1964; Nyman et al., 1988; Bogart
and Klemens, 1997; R.B., unpublished data), their interactions, and the conservation
implications of these interactions, need to be studied.
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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