Ambystoma talpoideum (Holbrook, 1838b)
Stanley E. Trauth
1. Historical versus Current Distribution. Mole salamanders (Ambystoma talpoideum) are distributed along the southern Atlantic and Gulf Coastal Plains from central South Carolina to eastern Texas, and north along the Mississippi River Valley to southern Illinois (Owens, 1941; Baldauf and Truett, 1964; Robison and Winters, 1978; Erwin, 1979; Sutton and Paige, 1980; Bader and Mitchell, 1982; Redmond et al., 1982; Braswell, 1985; Murdock and Braswell, 1985; Seyle, 1985a; Meshaka and McLarty, 1988; Meshaka et al., 1989; Braswell et al., 1990; Somers, 1990; Teska, 1990; Trauth et al., 1993a; Conant and Collins, 1998; Jensen, 1998; Petranka, 1998). They do not occur in southern peninsular Florida or in southern Louisiana. Disjunct populations are scattered in Kentucky, Virginia, Tennessee, North Carolina, northern South Carolina, northern Georgia, and northern Alabama. There is no evidence that this current distribution differs substantially from the historical distribution.
2. Historical versus Current Abundance. According to Petranka (1998) a large number of local ambystomatid populations have been lost in the conversion from mesic forest habitats to agriculture and urban areas. Clearcutting has been shown to affect mole salamander survival (Raymond and Hardy, 1991).
3. Life History Features.
A. Breeding. Reproduction is aquatic.
i. Breeding migrations. Breeding occurs primarily from December–March (Allen, 1932; Carr, 1940a; Gentry, 1955; Shoop, 1960; Mount, 1975; Hardy and Raymond, 1980; Walls and Altig, 1986; Trauth et al., 1993a, 1995b). Smith (1961) reported a November breeding aggregation. Variation in the timing of breeding migrations is related to annual variation in meteorological conditions (Gibbons and Semlitsch, 1991).
Neotenic adults do not migrate. Terrestrial adults migrate on rainy nights (Patterson, 1978; Semlitsch, 1981, 1985a,b, 1987). Breeding is most intense during periods of heavy, sustained rains and cold temperatures (Shoop, 1960; Petranka, 1998). Adults move along hardwood corridors, avoiding open grassy areas (Patterson, 1978).
Shoop (1960) reported that breeding of metamorphic adults lasted 7–15 d in any year. In contrast, Hardy and Raymond (1980) report that individuals remain in or near wetlands for anywhere between 8–108 d. They note that males arrive earlier and remain longer; however, both sexes leave the ponds at about the same time.
The timing of breeding appears to vary between neotenic and metamorphic animals. Peak breeding occurs earlier in neotenic animals—early November—compared with metamorphosed adults—middle November to early January . This temporal separation may produce partial reproductive isolation (see Petranka, 1998). Sperm are present within the spermathecae of metamorphosed adults from November–February (Trauth et al., 1994). These authors also mention the possibility of intermorph mating.
ii. Breeding habitat. In general, adults breed in forested, fishless wetlands (Semlitsch, 1988). These wetlands include a range of wetland classes—seasonal, semipermanent, and permanent (including Carolina bays)—gravel pits, and roadside ditches (see Petranka, 1998).
i. Egg deposition sites. Egg clusters are laid on small twigs or other submerged structures. When laying, females grasp a twig and lay eggs along its length (Shoop, 1960). Eggs are deposited at night, and females require several days to complete laying (Shoop, 1960; Krenz and Sever, 1995; see also Petranka, 1998). Most adults breed annually (Raymond and Hardy, 1990; Semlitsch et al., 1993). Adults exhibit philopatry (Raymond and Hardy, 1990).
Mole salamanders from the Atlantic and Gulf Coastal Plains also differ in their mode of egg deposition. Atlantic Coastal Plain populations lay their eggs singly and scatter them throughout the wetland (Semlitsch and Walls, 1990), while Gulf Coastal Plain populations lay their eggs in small clusters.
Breeding adult numbers (100–6,000 individuals; see Gibbons and Semlitsch, 1991) are related to recent rainfall, not the number of recently produced offspring (Semlitsch, 1987; Semlitsch et al., 1996).
ii. Clutch size. Clutch size in mole salamanders averages higher in Atlantic Coastal Plain populations. For example, in South Carolina eight clutches from metamorphosed females ranged from 481–696 (mean = 590) eggs, while clutches from seven metamorphosed females from Louisiana ranged from 208–504 (mean = 331) eggs (Raymond and Hardy, 1990). Similarly, Shoop (1960) found a range from 226–441 (mean about 300) eggs from 14 Louisiana female mole salamanders. Within regions, both clutch size and egg size increased with the size (age) of females (Semlitsch, 1985b; Semlitsch and Gibbons, 1990). Neotenic females are smaller than metamorphosed females and correspondingly lay fewer (mean = 173), smaller eggs (Petranka, 1998).
The number of eggs/cluster varies depending on the population: Bishop (1943) reports 4–20 eggs, Raymond and Hardy (1990) report both 5–50 eggs (38 clusters) and a mean of 18 eggs (107 clusters). In Arkansas, clutches from metamorphosed females contain from 12–99 (mean = 41) eggs. Neotenic females lay eggs singly (Trauth et al., 1995b; see also Petranka, 1998).
i. Length of larval stage. Larval growth is positively related to egg size and hatchling size (Walls and Altig, 1986). Smith (1961) reports a larval period of 3–4 mo. Recently metamorphosed individuals range from 35–38 mm SVL in Louisiana populations (Raymond and Hardy, 1990). Parmalee (1993) first noted newly metamorphic animals in July; numbers peaked in September. At the Savannah River Ecology Lab (see Semlitsch, 1985b), larvae grow rapidly after hatching, begin to mature as neotenic adults by September, and can breed as 1 yr olds in December–January. Here, animals that metamorphose do so from May–September and become sexually mature a few months later. A subset of animals overwinter as larvae and metamorphose the following spring. Pond drying triggers metamorphosis in large larvae and neotenic adults (Semlitsch and Gibbons, 1985; Semlitsch and Wilbur, 1988; Semlitsch et al., 1990).
ii. Larval requirements.
a. Food. As with all ambystomatids, mole salamander larvae are gape-limited. They feed primarily on zooplankton when young (small) and add larger prey items to their diet as they are able to ingest them (Taylor et al., 1988). Larvae are size-selective, choosing larger prey. While feeding at night, larvae stratify (move into the water column; Anderson and Williamson, 1974). In Mississippi, Branch and Altig (1981) report the consumption of copepods, cladocerans, Ambystoma larvae, and ostracods. In Arkansas, neotenic individuals consume mostly midge larvae and scuds, but will also cannibalize eggs and take the larvae of other Ambystoma species (McAllister and Trauth, 1996b).
b. Cover. During daylight hours, larvae remain hidden in leaf litter, vegetation, and debris on the bottom of ponds. At night, larvae leave these retreats to search for food (Anderson and Williamson, 1974).
iii. Larval polymorphisms. Not reported.
iv. Features of metamorphosis. Animals that metamorphose do so from May–September and become sexually mature a few months later. A subset of animals overwinter as larvae and metamorphose the following spring. Pond drying triggers metamorphosis in large larvae and neotenic adults (Semlitsch and Gibbons, 1985; Semlitsch and Wilbur, 1988; Semlitsch et al., 1990). In Louisiana, larval transformation occurs at 72–82 mm TL (Dundee and Rossman, 1989).
v. Post-metamorphic migrations. Undescribed.
vi. Neoteny. Populations that breed in permanent, fishless wetlands tend to be paedomorphic (see Petranka, 1998). In Arkansas, seasonal, temporary gravel pits of permanent, murky water also contain paedomorphic individuals (Trauth et al., 1993a).
D. Juvenile Habitat. Likely to be similar to adults. In contrast with adults, juveniles exhibit little agonistic behavior either towards conspecifics or heterospecifics (Walls, 1990). Most post-metamorphic growth occurs during the year following metamorphosis and prior to sexual maturity (Raymond and Hardy, 1990).
E. Adult Habitat. Adults can be metamorphosed or neotenic, and local populations can consist of either morphotype. Terrestrial adults are found in expansive floodplain forests—in areas near gum and cypress ponds (Shoop, 1960; Semlitsch, 1981). Outside the Atlantic and Gulf Coastal Plains, mole salamanders inhabit forested uplands, including mixed conifer-hardwood forests. The presence of fishless wetlands for breeding is important. Populations associated with seasonal and/or semipermanent wetlands produce terrestrial adults, populations associated with permanent wetlands produce neotenic adults (Semlitsch and Gibbons, 1985; Semlitsch et al., 1990; Scott, 1993; Heintzel and Rossell, 1995; see also Petranka, 1998).
Adult mortality varies from 16–37% (mean = 26%) and is the same for males and females (Raymond and Hardy, 1990). According to Patterson (1978), 45% of adults die before leaving the breeding wetland.
F. Home Range Size. Home range size is based upon the number of activity centers within a variety of terrestrial habitats; of 22 monitored individuals, 66% of their time was spent in pine forests and 33% in hardwood forests (Semlitsch, 1981). Males and females average 5.0 (range 1–6) activity centers and 3.0 (range 3) activity centers, respectively. In juveniles, the number is 2 (range 1–3). Areas of minimal home range size for males, females, and juveniles average 3.61, 5.29, and 0.25 m2, respectively (Semlitsch, 1981).
G. Territories. Unknown.
H. Aestivation/Avoiding Dessication. Aestivation is unknown; animals likely avoid dessicating condition by seeking shelter under cover objects or burrowing.
I. Seasonal Migrations. Environmental conditions have the greatest influence on seasonal migrations to breeding ponds; adults migrate only at night or shortly after rainfall (Semlitsch et al., 1993). Peak immigration is associated with the coldest period of the year in South Carolina (Semlitsch, 1985a). Emigration of breeding adults does not occur until March. Emigration of metamorphosing juveniles occurs from June–November (Semlitsch, 1985a). Average migration distance for adults is 178 m, juveniles, 47.0 m (Semlitsch, 1981, 1988).
J. Torpor (Hibernation). Unknown.
K. Interspecific Associations/Exclusions. Adult metamorphic animals breed in ponds utilized by marbled salamanders (A. opacum), spotted salamanders (A. maculatum), and eastern newts (Notophthalmus viridescens louisianensis) in Arkansas (Trauth et al., 1993a, 1995b). In Carolina bays (see Gibbons and Semlitsch, 1991) of South Carolina, several salamander and anuran species inhabit the same breeding sites as mole salamanders, including marbled salamanders, eastern newts, tiger salamanders (A. tigrinum), dwarf salamanders (E. quadridigitata), southern toads (Bufo terrestris), spring peepers (Pseudacris crucifer), southern chorus frogs (P. nigrita), little grass frogs (P. ornata), green frogs (Rana clamitans), southern leopard frogs (R. sphenocephala), and eastern spadefoot toads (Scaphiopus holbrookii; Semlitsch et al., 1996).
L. Age/Size at Reproductive Maturity. Individuals first breed at about 2 yr old, at ≥ 44 mm SVL (Shoop, 1960; Raymond and Hardy, 1990). In South Carolina, maturity in aquatic and terrestrial morphs is reached at 30 mm SVL (Semlitsch, 1985b).
M. Longevity. Individuals can live > 9 yr (Gibbons and Semlitsch, 1991).
N. Feeding Behavior. Mole salamanders feed on a variety of invertebrates (Petranka, 1998). Gibbons and Semlitsch (1991) report zooplankton, aquatic insects, and tadpoles in their diet.
O. Predators. Semlitsch (1988) reports that bluegills (Lepomis macrochirus) will feed heavily on mole salamander eggs. Exposure to caged fish produces a higher rate of metamorphosis (Jackson and Semlitsch, 1993).
P. Anti-Predator Mechanisms. When attacked, metamorphosed juveniles and adults exhibit a head-down posture and expose their well developed parotid glands to predators. The parotoid glands secrete noxious chemicals. Mole salamanders will also lash their tails at predators (Brodie, 1977). Petranka (1998) describes head butting, biting, and body flipping followed my immobility or fleeing when artificially exposed to a smooth earth snake (Virginia valeriae).
Q. Diseases. Unknown.
R. Parasites. Baker (1987) reports the occurrence of nematodes. Small encapsulated nematodes were found in one of five adults in an Arkansas population (C.T. McAllister, personal communication). Upton et al. (1993) mention the absence of coccidian parasites in mole salamanders from 12 specimens in three Arkansas counties.
4. Conservation. Mole salamanders have a core distribution centered on the Atlantic and Gulf Coastal Plains, with disjunct populations occurring peripherally. They are listed as a species of Special Concern in North Carolina, and a permit is required for all activities involving this species. Similarly, mole salamanders are classified as a species In Need of Management in Tennessee, where a permit is also required for all activities involving these animals. While the conversion of mesic forests to agricultural and urban/suburban areas has destroyed many populations of ambystomatid salamanders (Petranka, 1998), and while clearcutting reduces mole salamander numbers (Raymond and Hardy, 1991), there are no data showing that the current distribution of mole salamanders differs from their historical distribution.
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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