The following account is modified from Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo (©2005 by the Regents of the University of California), used with permission of University of California Press. The book is available from UC Press.

Ambystoma texanum (Matthes, 1855)
            Small-Mouthed Salamander

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.
            A. Breeding.
                        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, 1996).
                        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 explosive breeders.
            B. Eggs.
                        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).
            C. Larvae/Metamorphosis.
                        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 larvae.
                                    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.
            D. Juvenile Habitat.  According to Petranka (1998) juveniles use leafy cover objects more than will adults.
            E. Adult 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).
            G. Territories.  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).
            H. Aestivation/Avoiding Dessication.  Adults respond to hot, dry conditions by burrowing underground (Parmalee, 1993; see also Petranka, 1998).
            I. Seasonal Migrations.  Adults migrate to and from breeding ponds; juveniles exhibit post-metamorphic migrations (see Petranka, 1998).
            J. Torpor (Hibernation).  Unknown.
            K. Interspecific 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).
            M. Longevity.  Unknown.
            N. Feeding 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).
            O. Predators.  Include predaceous aquatic insects, tiger salamander larvae (Wilbur, 1972), garter snakes (Thamnophis sp.), and water snakes (Neroidia sp).
            P. Anti-Predator 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.
            R. Parasites.  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 sources.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 19 Apr 2024.

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