Ambystoma texanum (Matthes, 1855)
Stanley E. Trauth
1. Historical versus Current Distribution. Small-mouthed salamanders
(Ambystoma texanum) are distributed throughout the south-central United
States, except the Ozark Plateau and the Louisiana Gulf Coastal Plain (Scott and Johnson,
1972; Lardie and Glass, 1975; Neck, 1980b; Saugey et al., 1986; Cochran and Cochran,
1989; Fletcher and Cochran, 1990; Conant and Collins, 1998; Petranka, 1998; Petzing and
Phillips, 1998b). Populations range from southeastern Nebraska and Oklahoma,
eastern Oklahoma and Texas to southeastern Michigan and northern Ohio, and south to
eastern Kentucky, Tennessee, and western Alabama. Disjunct populations occur in
southern Ohio and Indiana, primarily along the Ohio River. There is little
evidence that the current distribution differs from the historical distribution, although
interpreting this is complicated because some populations historically considered
small-mouthed salamanders have been determined to be streamside salamanders (A.
barbouri; Kraus and Petranka, 1989; see also Petranka, 1998).
2. Historical versus Current Abundance. Typically reported as abundant,
especially from observations made during the breeding season (e.g., Bragg, 1955b).
According to Petranka (1998), populations of small-mouthed salamanders have been
eliminated throughout their range as floodplain and mesic forests have been clearcut and
converted to agricultural uses.
3. Life History Features.
i. Breeding migrations. Adult small-mouthed salamanders migrate from upland sites
to breeding wetlands during warm rains from late winter to early spring (B.A. Brown et
al., 1982; Petranka, 1984a; Kraus and Petranka, 1989), although adults will migrate in
the absence of rains during drought conditions (Bailey, 1943). Breeding occurs
earlier in the south (for breeding dates see Hay, 1892; Gloyd, 1928; Smith, 1934; Cagle,
1942; Bailey, 1943; Bragg, 1949; Ramsey and Forsyth, 1950; Smith, 1961; Brandon, 1966a;
Minton, 1972, 2001; Plummer, 1977; B.A. Brown et al., 1982; Downs, 1989f; Doody,
ii. Breeding habitat. Adults breed in fishless seasonal and semipermanent wetlands
including prairie potholes, forested wetlands, oxbows, ditches, borrow pits, flooded
fields, and occasionally stream pools (Gloyd, 1928; Burt, 1938a; Cagle, 1942; Bailey,
1943; Ramsey and Forsyth, 1950; Petranka, 1982a, 1998; Kraus and Petranka, 1989; Collins,
1993). As with many species of ambystomatids, small-mouthed salamanders are
i. Egg deposition sites. Typically in water, but Moore and Matson (1997) found
eggs suspended from buttonbush (Cephalanthus occidenatils)
branches. Females lay eggs either singly or in clusters ranging from 2–15
eggs (Bailey, 1943; Minton, 1972, 2001; Petranka, 1982a; Licht, 1989; Trauth et al.,
1990; see also Petranka, 1998). Surprisingly, the courtship pattern of
small-mouthed salamanders has been controversial, which means it is probably
variable. Working in McLean County, Illinois, Wyman (1971) observed that males
combine rubbing and amplexus to stimulate females. Working in Jackson County,
Illinois, Garton (1972) reports that similar to spotted salamanders (Ambystoma
maculatum) and ringed salamanders (A. annulatum),
small-mouthed salamander males deposit a large number of spermatophores in a small area,
into which females enter then mount the spermatophores. Garton (1972) does not
observe amplexus nor males leading females over spermatophores and attributed these
differences to introgression with blue-spotted salamanders (A.
laterale). Licht and Bogart (1990) confirmed Garton's (1972) report of the
absence of amplexus in small-mouthed salamanders, but rejected his hypothesis that this
was due to introgression with blue-spotted salamanders.
ii. Clutch size. Females are reported to carry from 550–700 eggs (Smith,
1934; Cagle, 1942; Burger, 1950; Camper, 1990). Eggs range from 1.6–2.5
mm. Incubation lasts from 2–8 wk, depending on temperature (Minton, 1972,
2001; see also Petranka, 1998).
i. Length of larval stage. Newly hatched larvae vary from 7–14 mm TL (Smith,
1934; Liner, 1954; Minton, 1972, 2001; see also Petranka, 1998) and metamorphose between
2–4 mo later at about 60 mm TL (Hay, 1892; Bragg, 1949; Rossman, 1960; Minton,
1972, 2001; Parmalee, 1993; see also Petranka, 1998).
ii. Larval requirements.
a. Food. Larvae are gape-limited and feed on cladocerans and ostracods when young
(small) and larger prey such as insect larvae, isopods, and gastropods when older.
Larvae feed dielly (day and night) and will occasionally cannibalize (Minton, 1972,
2001; Whitaker et al., 1982; McWilliams and Bachmann, 1989a). While Petranka (1998)
emphasized that larvae feed on the surface of the leaf litter on the pond bottom,
McWilliams and Bachmann (1989b) noted foraging in the water column, especially by smaller
b. Cover. During the day, larvae seek cover under leaf litter on the wetland
bottom (Petranka, 1998). Kats (1988) noted that small-mouthed salamander larvae
detect potential predators using olfactory cues.
iii. Larval polymorphisms. Unknown and unlikely per se, given the extent of the
work done on small-mouthed salamanders. However, Underhill (1968b) suggests that
there is a recessive gene for albinism maintained at a low frequency in central Illinois
populations that produce albino eggs and larvae.
iv. Features of metamorphosis. Size at metamorphosis averages 48 mm TL (Bragg,
1949). Metamorphosis generally occurs from late May to July (see Petranka,
1998). Brandt (1947) reports that associative memory related to larvae feeding
survives metamorphosis and is present in adults.
v. Post-metamorphic migrations. Within a few weeks of metamorphosis, small-mouthed
salamanders migrate to cover objects on the floors of floodplain and mesic forests.
They move to nearby underground sites in response to hot, dry conditions (Parmalee,
1993; see also Petranka, 1998). Juveniles do not move far from their breeding
ponds, and adult small-mouthed salamanders remain closer to their breeding ponds than
will other ambystomatid species (Parmalee, 1993).
vi. Neoteny. Unknown and unlikely.
Habitat. According to Petranka (1998) juveniles use leafy cover objects more than
Habitat. Adult small-mouthed salamanders spend most of their time in burrows in
mesic forest floors, including crayfish burrows, near the breeding wetlands (Strecker and
Williams, 1928; Cagle, 1942; Minton, 1972, 2001; Parmalee, 1993; see also Petranka,
1998). They surface during rainy nights. During breeding early in the
spring, adults can be found beneath logs or other cover objects near the wetland
margins. Adults tend to be found under larger cover objects and frequently share
cover objects with conspecifics, infrequently with congenerics. Adults are sometimes
unearthed by plows and excavation equipment.
F. Home Range
Size. Data show that adults remain in the same area (maximum distance moved by a
female = 20 m) for long periods (Petranka, 1998).
Adult small-mouthed salamanders do not appear to establish territories (Martin et al.,
1986; Parmalee, 1993); they do not respond to substrates marked by conspecifics nor show
aggression to conspecifics (see also Petranka, 1998).
Aestivation/Avoiding Dessication. Adults respond to hot, dry conditions by
burrowing underground (Parmalee, 1993; see also Petranka, 1998).
Migrations. Adults migrate to and from breeding ponds; juveniles exhibit
post-metamorphic migrations (see Petranka, 1998).
Associations/Exclusions. Adults share breeding wetlands with spotted salamanders,
marbled salamanders (A. opacum), and mole salamanders (A.
talpoideum). Adults appear to segregate by moisture levels, with
small-mouthed salamanders and mole salamanders found in wetter sites. Larval
numbers of small-mouthed salamanders are reduced in the presence of tiger salamander
(A. tigrinum) larvae.
Populations of silvery salamanders (A. platineum) from east-central Illinois
and central Indiana occur where Jefferson salamanders are absent and small-mouthed
salamanders (A. texanum) are the sexual host (Uzzell and Goldblatt,
1967). In at least one of these populations, JJL eggs of silvery salamanders are
regularly fertilized by small-mouthed salamander sperm resulting in tetraploid hybrids
that are JJLT (Morris and Brandon, 1984; Spolsky et al., 1992). Phillips et al.
(1997) also documented pentaploids in this population that are presumably the result of
fertilization of JJLT eggs by A. texanum sperm (JJLTT; see
Unisexual Ambystoma account in this volume).
L. Age/Size at
Reproductive Maturity. Small-mouthed salamanders reach sexual maturity at
60–70 mm SVL, with a maximum size for females of 106 mm SVL (Redmer, 1995), but
time to maturity is unknown (Petranka, 1998).
Behavior. Small-mouthed salamander adults eat a wide variety of invertebrate prey
including annelids, isopods, centipedes, arachnids, lepidopterans, coleopterans, and
other insects. Breeding adults occasionally feed on aquatic invertebrates (Whitaker
et al., 1982; see also Petranka, 1998).
Include predaceous aquatic insects, tiger salamander larvae (Wilbur, 1972), garter snakes
(Thamnophis sp.), and water snakes (Neroidia sp).
Mechanisms. In response to attacks by snakes and other predators, individual adults
assume a defensive posture that includes lowering their head, curling their body, and
raising and waving their tail, which secretes noxious substances (Hay, 1892; Minton,
1972, 2001; Dodd, 1977b).
Q. Diseases. No
data are available on diseases in small-mouthed salamanders.
Parasites of small-mouthed salamanders include a variety of protozoan and helminth
species (Harwood, 1932; Walton, 1942; Landewe, 1963; Rosen and Manis, 1976; Price and St.
John, 1980; Baker, 1987; McAllister and Upton, 1987b). No intraerythrocytic or
trypanosomal hematozoans were observed in blood samples examined by McAllister and Upton
(1987b). Protozoans, however, have been reported from the colon, rectum, gall
bladder, intestinal mucosa, and feces (see studies cited above). A cyclophyllidean
cestode (Cylindrotaenia americana) that is common in several
plethodontid salamander species in the United States was also found in the small
intestine of small‑mouthed salamanders (McAllister and Upton, 1987b).
4. Conservation. Small-mouthed salamanders are listed as Endangered by the State
of Michigan, and legally protected under Michigan's Natural Resources and Environmental
Protection Act (Levell, 1997). These populations represent the northern extreme of
small-mouth salamander distribution. There are few data to suggest that their
current distribution differs from their historical distribution, although undoubtedly
many populations have been lost due to wetland drainage and deforestation due to
agricultural practices and urban/suburban development.
Acknowledgments. Thanks to Robert Fiorentino for providing additional
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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