Ambystoma maculatum (Shaw, 1802)
Basis for Listing
The Spotted Salamander (Ambystoma maculatum) is widely distributed across forested regions of the eastern United States and Canada, including the northern hardwood forests at the eastern edge of Minnesota. This species was first discovered in Pine County, Minnesota in 2001 (Hall 2002). In 2005, the Minnesota Biological Survey identified egg masses at several wetland locations along the Wisconsin border in Pine and Carlton counties (Mille Lacs Upland Subsection). Since that time, it has not been documented in any additional Minnesota counties. The Spotted Salamander is restricted to forested habitat with suitable breeding sites, such as small seasonal ponds or shallow emergent wetlands that do not contain fish. Potential threats to the species in Minnesota include loss of ephemeral wetland habitat, forest fragmentation, intensive timber harvest near breeding sites, and wetland acidification. Northwestern range progression in Minnesota may be limited due to the species’ intolerance to acidic conditions (Clark 1986). More information is needed on the distribution, abundance, and ecology of this species in Minnesota. For these reasons, the Spotted Salamander was designated a species of special concern in 2013.
The Spotted Salamander is a medium to large sized salamander, averaging 15-25 cm (6-10 in.) in total length (Petranka 1998), with females generally being larger than males (Downs 1989). The species has five toes on both front and hind feet. It is black or gray above, with an irregular double row of neatly edged circular yellow spots down the back and onto the tail; some of the spots near the head may be orange. The underside is gray and unmarked. The very similar-looking Eastern Tiger Salamander (Ambystoma tigrinum) and Barred Tiger Salamander (A. mavortium) both have olive colored undersides due to the infusion of black and yellow coloration from their flanks. In addition, the Spotted Salamander has a gray lower lip, while both the Tiger Salamander and Barred Tiger Salamander usually have yellowish or light colored lower lips. Upon emergence, larval Spotted Salamanders temporarily possess adhesive balancers that are used to steady the larvae until the front limbs develop; larval Tiger Salamanders lack balancers (Crawford and Wake 1998).
Mature deciduous, conifer, and mixed deciduous-conifer forests with embedded shallow seasonal ponds or shallow wetlands that do not contain predatory fish are common habitats for the Spotted Salamander (Petranka 1998). In other parts of its range, this species lives in bottomland floodplain forest, and some populations occur in upland forests in mountainous regions where appropriate wetlands for breeding are present (Petranka 1998). In Minnesota, this species has been found in the mesic hardwood forest of the Nemadji and St. Croix state forests. This species requires wetlands free of predatory fish for reproduction and mature closed-canopy forests that shade the forest floor and contain organic soils and woody debris where salamanders forage and shelter during the summer months. Associated amphibian species in Minnesota include the Blue-spotted Salamander (A. laterale), Four-toed Salamander (Hemidactylium scutatum), Eastern Red-backed Salamander (Plethodon cinereus), Spring Peeper (Pseudacris crucifer), and Wood Frog (Lithobates sylvaticus).
Biology / Life History
Courtship and mating of the Spotted Salamander typically takes place in April. Adult migration to breeding wetlands often coincides with spring rainfall and warming temperatures, though some migration can occur during damp and humid nights in the course of a dry spring. Some individuals may be highly philopatric (using the same pools, migration routes, and pool entrance/exit points each year). Males arrive slightly earlier in the spring and are 1.5 to 3.5 times more numerous in breeding ponds than females (Downs 1989; Hillis 1977). Adults may remain in the wetlands from a few days to five weeks (Windmiller 1996). Courtship involves the male circling and nudging the female with his snout. In dense populations, courting salamanders may repeatedly break the surface of the water. Egg laying begins within 2-3 days after mating (Petranka 1998). Each female lays up to four egg masses consisting, on average, of 60-100 eggs. Each egg mass is attached to submerged vegetation, twigs, logs, or directly to the substrate. Communal nesting is known. Egg masses are firm and globular or cylindrical; the outer jelly layer may be clear, milky white, or intermediate in color depending upon the presence of certain proteins (Hardy and Lucas 1991; Ruth et al. 1993). A symbiotic unicellular green algae, chlamydomonad or salamander algae (Oophila amblystomatis), that increases oxygen supply to the embryos in the center of the mass and absorbs carbon dioxide by photosynthesis (Bachmann et al. 1986) is found within the outer jelly membrane. This algae may also be present inside the salamander itself in all life stages. Egg incubation lasts from 4-7 weeks. The larval stage ranges from 2-4 months until metamorphosis, which occurs from early to mid-August through September. Metamorphs may remain at the wetland margin for a few weeks and often disperse into the surrounding woodland during a rain event. Sexual maturity occurs after two years (Vogt 1981), with most males attaining sexual maturity between two and five years and most females between three and seven years of age (Flagole and Leclaire 1992). Adults and juveniles utilize upland forest habitat during the summer months, remaining under dense forest litter or logs or in underground burrows. Terrestrial adults may remain unobserved except during early spring and fall nocturnal migrations amid wet weather. Fall migrations typically occur during September or October. Recorded longevity is from 18-32 years (mean 6-8 years; Flageole and Leclair 1992). Adults may defend burrows from conspecifics (Ducey and Heuer 1991) and aggression toward Eastern Red-backed Salamanders has been documented (Ducey et al. 1994). In Minnesota, predators of eggs and larvae include large aquatic insects, Wood Frog tadpoles, Eastern Tiger Salamander larvae, and fish. Predators of adults are numerous and include any large carnivorous mammal, particularly Raccoons (Procyon lotor); small carnivores, such as the Short-tailed Shrew (Blarina brevicauda); large birds; Common Gartersnake (Thamnophis sirtalis), and more. This species, when threatened, may secrete a noxious substance from glands along the back and tail. Harassed individuals may assume a defensive posture consisting of lowering the head, arching the back and tail, and tail waving accompanied by head butting and snapping. The Gray Treefrog (Hyla versicolor) has been observed to actively avoid breeding in pools used by the Spotted Salamander for reproduction (Resetarits and Wilbur 1989). Larvae feed upon zooplankton and aquatic invertebrates. Juveniles and adults consume a variety of terrestrial invertebrates, such as earthworms, insects, spiders, and mollusks (Petranka 1998).
Conservation / Management
The greatest threat to the Spotted Salamander, in both Minnesota and throughout its range, is the loss and degradation of wetlands that are free of predatory fish and adjacent closed canopy upland forest. In Maine, Spotted Salamanders were sensitive to even-aged harvesting and associated edge effects to a depth of 25-35 m (82-115 ft.), and some structural microhabitat variables relevant to forest management were identified as potentially limiting near forest edges, including canopy cover, litter cover, and a measure of stumps, snags, and their root channels (deMaynadier and Hunter 1995). Although a decline in this species has not been observed, limited surveys have revealed few populations in Minnesota. Optimal breeding sites are surrounded by closed canopy mesic hardwood forest. Any activity that results in opening the canopy may allow for the colonization of Tiger Salamanders, whose larvae are voracious predators of Spotted Salamander and other amphibian larvae. Detailed management guidelines are available to assist resource managers in reducing impacts and protecting key habitat features for the Spotted Salamander (Hall and Carlson 2004). Recommendations include a 50 ft. (15 m) no-cut buffer zone around wetlands known to be utilized for reproduction and the retention of a 50-150 ft. (15-46 m) buffer of some adjacent woodland. Slash, coarse woody debris, and treetops should be left in place or should be evenly distributed on site. Additionally, maintaining closed canopy corridors across the landscape is important for conserving upland habitat, and corridors between wetlands is important for migration and dispersal routes of this highly philopatric salamander. The impacts of forest roads and recreational trails should be minimized and not cross known breeding wetlands. Run-off from logging roads and trails into wetlands, vernal pools, and streams should be avoided. The establishment of logging roads and recreational trails should follow Minnesota Forestry Resources Council guidelines. The use of herbicides should be curtailed in or near known breeding sites. Management activities involving any soil disturbance should occur during winter months to minimize soil compaction, rutting, and impacts to salamanders.
Conservation Efforts in Minnesota
The Spotted Salamander is most readily detected in the spring by locating egg masses in ephemeral pools. Due to its secretive nature, changes in population trends are difficult to observe for this species without targeted surveys or monitoring initiatives. Few new locations for this species have been found since 2005, when the Minnesota Biological Survey worked in Pine County; therefore additional targeted surveys are required. More information regarding the abundance, distribution, seasonal patterns, and other ecological factors in Minnesota is needed.
Jeffrey B. LeClere (MNDNR), 2018
(Note: all content ©MNDNR)