© 2010 Dr. Stephen G. Tilley (1 of 20)
Country distribution from AmphibiaWeb's database: United States
Stereochilus marginatus (Hallowell, 1856)
Travis J. Ryan1
1. Historical versus Current Distribution. Many-lined salamanders (Stereochilus marginatus) inhabit wetlands, permanent lentic habitats, and slow-moving streams on the Atlantic Coastal Plain. The northern extreme of the distribution is southeastern Virginia, and they may be found as far south as northeastern Florida (Bishop, 1943; Schwartz and Etheridge, 1954; Neill, 1957e; Cooper, 1962; Rabb, 1966; Gerhardt, 1967; Christman et al., 1979b; Campbell et al., 1980; Petranka, 1998; Mitchell and Reay, 1999). Mitchell and Reay (1999) note that the northern portion of their range needs to be better determined; many-lined salamanders are one of the more poorly known plethodontid species in this fairly well-studied region. Loss of populations has undoubtedly occurred with wetland drainage (Petranka, 1998; Means, 2003a), but this has not been documented or quantified to any appreciable degree. Mitchell (1991) describes their conservation status as Undetermined.
2. Historical versus Current Abundance. Wetlands along the Atlantic Coastal Plain, where many-lined salamanders are found, are rapidly disappearing or being substantially altered (Means, 2000, 2003a). How this is affecting the many-lined salamander, however, is not yet known. It is worth noting, however, that the range of many-lined salamanders overlaps substantially with flatwoods salamanders (Ambystoma cingulatum), a species Federally listed as Threatened in 1999. While these species differ ecologically (e.g., flatwoods salamander adults are primarily terrestrial and migrate to breed in ephemeral wetlands), wetland conversion and destruction is likely a common primary threat to their long-term persistence.
3. Life History Features.
A. Breeding. Reproduction is aquatic and appears to follow the stereotypical behaviors associated with plethodontid salamanders with both tactile and chemical stimulation appearing mandatory. Noble and Brady (1930) make mention of a tail straddle walk and that males rub their mental glands over the nares of females. Beyond this, however, there is no detailed account of many-lined salamander courtship.
i. Breeding migrations. Negligible, if present at all. Because adults are primarily aquatic, they reside in the nuptial/natal site year-round. Many-lined salamanders are autumn breeders, and both sexes reproduce annually (Bruce, 1971).
ii. Breeding habitat. The same as general adult habitats: ponds, bogs, marshes, ditches, and slow-moving streams.
i. Egg deposition sites. Females oviposit during the winter in sites usually associated with aquatic habitats. Eggs are laid in either water or on land (Wood and Rageot, 1963; Bruce, 1971; see also Petranka, 1998). In water, eggs are attached singly to a support; in nature, to the lower surface of a stone, log, or piece of bark, 8–15 cm below the water surface in quiet pools (Bishop, 1943; Wood and Rageot, 1963); females do not brood. In the Dismal Swamp, where Sphagnum sp. moss is common, females show a preference for laying eggs on the water moss Fontinalis sp. (Wood and Rageot, 1963; see also Rabb, 1966). On land, eggs tend to be more clustered, and in about 30% of clutches females brood. Terrestrial nests have been found inside a decaying gum log near a pond margin (Rabb, 1956) and under a small log near a borrow pit (Schwartz and Etheridge, 1954; see also Petranka, 1998).
ii. Clutch size. Between 16–121 eggs are laid (Wood and Rageot, 1963; Bruce, 1971; see also Petranka, 1998; Ryan and Bruce, 2000) in most populations, but may average as many as 57 in a South Carolina population (Rabb, 1966). Eggs are 2–3.4 mm in diameter (Noble and Richards, 1932; Rabb, 1956). Hatchlings measure 8 mm SVL (Bruce, 1971). When compared with other generalized plethodontids, many-lined salamanders lay more eggs of smaller size in more ephemeral wet areas, likely a response to high larval mortality (Ryan and Bruce, 2000).
C. Larvae/Metamorphosis. Many-lined salamanders demonstrate a pond-like larval morphology, rare among plethodontids, including a high caudal fin extending onto the body, large filamentous gills, and a strongly invaginated gular fold (see Ryan and Bruce, 2000).
i. Length of larval stage. Larval size at hatching is about 8 mm, and larvae have functional limbs (Bruce, 1971; Ryan and Bruce, 2000). Growth is greater in the first year (about 15–16 mm SVL) than in the second (9–10 mm SVL). Larvae metamorphose either at the beginning of their second year (13–16 mo post hatching) or in the early part of their third year (25–28 mo post hatching; Bruce, 1971). Size at metamorphosis ranges between 27–40 mm SVL (Foard and Auth, 1990; Ryan and Bruce, 2000).
ii. Larval requirements.
a. Food. Larvae are carnivorous, feeding on small invertebrates associated with vegetation beds (see Petranka, 1998). In the only published study of the diet of many-lined salamanders, Foard and Auth (1990) found isopods to be the most common food item in the gut of the larvae. Other aquatic invertebrate taxa documented were (in order of decreasing occurrence) chironomid larvae, ostracods, amphipods, copepods, dytiscid beetles, and cladocerans. The diet of larvae differs significantly from that of adults (see "Feeding Behavior" below).
b. Cover. Larvae are most commonly found in the aquatic vegetation at the periphery of wetlands, such as Sphagnum mats or Fimbristylis (Rabb, 1966; Bruce, 1971; Foard and Auth, 1990).
iii. Larval polymorphisms. Unknown and unlikely.
iv. Features of metamorphosis. In North Carolina populations, metamorphosis occurred after 1 or 2 yr of development when larvae were 27–42 mm SVL (Bruce, 1971). In Georgia, metamorphic individuals measured between 30 and 35 mm SVL (Foard and Auth, 1990), presumably also 1 or 2 yr post hatching. While Bruce indicated that metamorphosis is most common in spring and summer, there are no corresponding data on timing of metamorphosis for the Georgia population.
v. Post-metamorphic migrations. Most pond-breeding salamanders (e.g., those of the genera Ambystoma and Notophthalmus) migrate from the nuptial/natal site following metamorphosis; many-lined salamanders are a clear exception to this trend. Juveniles and adults are primarily aquatic and appear to stay within or at least near the pond of origin.
vi. Neoteny. Perennibranchism, the retention of external gills throughout life, is not known, but these aquatic salamanders demonstrate some degree of reproductive acceleration when compared to their closest relatives in the genera Gyrinophilus and Pseduotriton (Ryan and Bruce, 2000).
D. Juvenile Habitat. Because post-metamorphic individuals are still predominantly aquatic, the larval, juvenile, and adult habitat characteristics are essentially the same (see Petranka, 1998).
E. Adult Habitat. Many-lined salamanders are usually aquatic, especially in permanent water, but occasionally found on land under logs in damp situations (Brimley, 1909, 1939; Bishop, 1943; Rabb, 1966; Bruce, 1971; Foard and Auth, 1990). Means (2000) refers to these animals as "technically a wetland species" living their entire larval and metamorphosed life in shallow, acid waters of Lower Coastal Plain swampy streams, coming onto land only occasionally. Most abundant in pools and slow streams such as gum and cypress swamps, woodland ponds, borrow pits, canals, and drainage ditches. Ryan and Bruce (2000), following Rabb (1966), note they are usually restricted to swamps, ditches, and sluggish streams of the Atlantic Coastal Plain. Animals can be collected by raking out dead leaves and detritus or by searching in and under Sphagnum sp. mats (Bishop, 1943; Rabb, 1966). However, adults occasionally are captured terrestrially.
F. Home Range Size. No studies to date have investigated home range size (or even the presence thereof) in many-lined salamanders.
G. Territories. Unknown. However, it may be safe to speculate that many-lined salamanders do not maintain distinct territories as opposed to many other plethodontid salamanders that are highly territorial. Because these are aquatic salamanders, marking territories via conventional methods (see Jaeger, 1988; Jaeger and Forrester, 1993) is problematic.
H. Aestivation/Avoiding Dessication. Foard and Auth (1990) reported digging up many-lined salamander adults from exposed riverbeds during drought conditions. Individuals were found singly in small cavities measuring “about two-thirds their body length and twice their body width.” It is unknown how long the individuals were in these cavities or how long they would be capable of remaining there.
I. Seasonal Migrations. Because of the almost exclusively aquatic life style, seasonal migrations are unlikely.
J. Torpor (Hibernation). Unlikely, given that many-lined salamanders live in a region that does not regularly experience extended sub-freezing temperatures.
K. Interspecific Associations/Exclusions. According to Petranka (1998), many-lined salamanders are found in association with other amphibians, but competitive and/or predatory interactions are poorly understood. Means (2000) notes that many-lined salamanders are found in association with mud salamanders (Pseudotriton montanus), dwarf salamanders (Eurycea quadridigitata), and southern dusky salamanders (Desmognathus auriculatus). Other species found by Bruce (1971) to be in association with many-lined salamanders include lesser sirens (Siren intermedia), two-toed amphiumas (Amphiuma means), and several anurans such as southern cricket frogs (Acris gryllus), southern leopard frogs (Rana sphenocephala), and carpenter frogs (R. virgatipes).
L. Age/Size at Reproductive Maturity. In males, maturation follows metamorphosis. In females, maturation is delayed until 1 yr following metamorphosis. Therefore, males reproduce in the autumn following metamorphosis, when about 21–33 mo old and 33–40 mm SVL (Bruce, 1971; Ryan and Bruce, 2000). Unlike males, females remain juveniles for > 1 yr after metamorphosing and do not reproduce for the first time until 3 or 4 yr old and between 37–45 mm SVL (Bruce, 1971; Ryan and Bruce, 2000). Adults range from 63–112 mm TL, with slightly < 1/2 length being tail (Rabb, 1966). Despite the asynchrony in the attainment of maturation, there appears to be no sexual size dimorphism (Bruce, 1971; see also Petranka, 1998).
M. Longevity. Unknown.
N. Feeding Behavior. While they share the same habitat, the prey of post-metamorphic many-lined salamanders differs from larvae in terms of the diversity of prey taken and the relative abundances. Only seven taxa were represented in the guts of larvae, whereas twice as many taxa were present in the gut of adults (Foard and Auth, 1990). The most common prey items were still isopods (52% of all stomachs investigated; only 37% in larvae), with amphipods a distant second (21%). No other taxa were represented in > 5% of the 161 transformed individuals examined. Most of the time, transformed individuals feed off the bottom, consuming larger prey items than larvae. However, they are capable of feeding off the surface, as long as their limbs are in contact with the substrate, and may in fact feed on terrestrial invertebrates (e.g., lepidopterans, coleopterans, chilipodans, and formicidians) during periods of heavy rainfall. Foard and Auth (1990) speculated that the terrestrial invertebrates were swept into the aquatic habitats during the rainfall, but because adults are known to occasionally leave wetlands (which would be most likely during periods of significant rainfall) it should not be ruled out that some terrestrial feeding occurs.
O. Predators. Unknown, but Petranka (1998) states that natural predators probably include aquatic snakes, fishes, wading birds, and invertebrates such as dragonfly naiads and dytiscid beetle larvae. Bruce (1971) documented several species of snakes in many-lined salamander habitats, including at least two species, southern watersnakes (Nerodia fasciata) and black swampsnakes (Seminatrix pygaea), likely to feed on aquatic salamanders.
P. Anti-Predator Mechanisms. Many salamanders are well known for their defensive displays and postures (e.g., Brodie, 1977), but virtually all species for which such behaviors are known are at least partially, if not altogether, terrestrial. Defensive displays are likely ineffective in murky waters such as those inhabited by many-lined salamanders. Accordingly, there is not record of defensive posturing in this species, and it is unlikely that such behaviors exist.
Q. Diseases. Unknown.
R. Parasites. Gut parasites were common in Foard and Auth’s (1990) samples; nearly half of all the guts examined contained at least one endoparasite, most commonly the acanthocephalan, Pilum pilum. They speculate that parasitism was a result of gastropod ingestion; however, they did not record gastropods in the gut contents of any animals investigated.
4. Conservation. Many-lined salamanders are one of the more poorly known plethodontids. Loss of populations has undoubtedly occurred with wetland drainage, but this has not been documented. Mitchell (1991) describes their conservation status as Undetermined. Wetland destruction is likely a primary threat to their long-term persistence.
1Travis J. Ryan
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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