Description This salamander is relatively large (85-185 mm total length), usually with 16 costal grooves. The dorsal ground color is slate gray to bluish black, with a gray belly. In three of the four population isolates, this species has a black body with bright red coloration on the dorsal surfaces of the legs. In the Unicoi Mountains it rarely has red coloration on the legs, but has lateral white spotting (Weisrock et al. 1995). Sexually active males have obvious, rounded mental glands (Petranka 1998). Young juveniles may have paired red spots running along the back (Wood 1947).
Plethodon shermani occurs in four disjunct, high-elevation populations in the Unicoi and Nantahala mountains, within the southern Appalachians (Weisrock et al. 2005). The range lies primarily in North Carolina (Lannoo 2005), but also extends just into northern Georgia (Graham et al. 2007), and barely into southeastern Tennessee, where a P. shermani-P. aureolus hybrid population occurs on Sassafras Ridge (Weisrock et al. 2005). This species was formerly treated as P. jordani, and the populations now considered P. shermani represent the Standing Indian, Wayah, Tusquitee, and Unicoi Mountain isolates of the P. jordani complex (Highton and Peabody 2000). It is found in mountainous, cool, mesic forests (Petranka 1998) from 853-1,494 m above sea level (Highton and Peabody 2000).
Life History, Abundance, Activity, and Special Behaviors
This species shelters under logs or rocks by day, and forages on the forest floor at night (Petranka 1998).
Courtship for salamanders in the P. jordani complex has been observed in the field from mid-July through early October (e.g., Arnold 1976; Hairston 1983, Organ 1958). Females have a biennial reproductive cycle and mate every other year (Arnold 1976). Nests have not been found, indicating that gravid females likely oviposit deep underground (Petranka 1998). Oviposition probably takes place around May, judging from the presence/absence of gravid females in collection samples (Hairston 1983) and hatching is likely to occur in the late summer or early autumn, 2-3 months after egg deposition (Petranka 1998).
Feeding trials have shown that Red-legged Salamanders have slimy tails which are unpalatable to potential avian predators (Brodie and Howard 1973; Hensel and Brodie 1976; Huheey 1960). The red coloration may thus be aposematic (Petranka 1998, under comments in P. jordani account). However, Petranka (1998) points out that experimental work has not yet shown strong support for this hypothesis (Hensel and Brodie 1976; Labanick and Brandon 1981). The sympatric species Desmognathus ocoee has red-legged (as well as yellow and orange-legged) morphs, but is palatable to predators, and may possibly be mimicking P. shermani (Petranka 1998; Labanick and Brandon 1981).
Trends and Threats Plethodon shermani can tolerate some habitat fragmentation, since their home ranges are small and they do not migrate to breeding ponds. They are also amenable to living in second-growth forest (Lannoo 2005).
Comments The species authority is: Stejneger, L. 1906. "A new salamander from North Carolina." Proceedings of the United States National Museum 30: 559–562.
Amphibious mating in the Red-legged Salamander, Plethodon shermani.
This clip shows pheromone transfer from male to female during salamander courtship, late in the courtship sequence. The female (on the left) is straddling the tail of the male (on the right). The male turns and performs a head-slap, which transfers pheromonal secretions from the mental gland under the male's chin to the female.
Video submitted by: Stevan Arnold.
Amphibious sperm transfer in the Red-legged Salamander, Plethodon shermani.
Courtship is in the final stages. After the head-slap sequence shown in the previous clip, the female continues to straddle the male's gently undulating tail, while resting her chin on the dorsal surface of the base of his tail. After a few moments, the male deposits a white spermatophore on the substrate, then moves forward and away. The female moves forward, keeping her chin on his tail base, until her vent area is over the spermatophore, then backs up, lowers her vent, and picks up the spermatophore with her cloaca.
Run time: 00:52.
Video submitted by: Stevan Arnold.
Plethodon shermani has been used to investigate pheromone involvement in salamander courtship. Salamanders primarily have internal fertilization (about 90% of species) but do not have an intromittent organ, instead depositing a spermatophore which the female must choose to pick up as part of the complex mating behavior. Although many vertebrates use chemical signals (pheromones) to communicate during reproduction, only in salamanders have pheromones been demonstrated to affect female receptivity. Courtship pheromones are produced by male salamanders via the mental gland (in terrestrially breeding species), an enlarged glandular pad located under the chin, or via the cloaca into the water (in aquatically breeding salamanders). Courtship pheromones function after the initiation of courtship, specifically increasing the likelihood of the particular courted female's participation in mating, and thus also increasing the male's insemination success. This is in contrast to more general sex attractants which function generally to attract any potential mates, prior to courtship initiation. In plethodontid salamanders, which breed terrestrially, these pheromones are delivered by the male's bringing the submandibular mental gland in direct contact with the female's nasal region. The pheromones then migrate via the female's nasolabial grooves (these grooves are found only in plethodontid salamanders) into her vomeronasal organ (Houck et al. 2007).
This species has also been the focus of a number of neurobiological studies: elucidating the mechanism of pheromonal communication in salamanders (e.g. Wirsig-Wiechmann et al. 2002, Wirsig-Wiechmann et al. 2006), brain-specific expression of the amphibian homologues of mammalian vasopressin and oxytocin (Hollis et al. 2005), and the neurobiology of visual object recognition (e.g. how amphibian visual neurons are involved in recognizing prey; Schuelert and Dicke 2005).
This species was separated from P. jordani by Highton and Peabody (2000). Mitochondrial data shows that some population isolates of Plethodon shermani (the Unicoi isolate in particular, and the Tusquitee isolate to a lesser degree) show significantly more introgression, from hybridization with salamanders of the Plethodon glutinosus complex (Weisrock et al. 2005). This hybridization represents both recent and historical contact (Weisrock et al. 2005).
The most extensive current hybridization takes place between Plethodon shermani and P. teyahalee (Highton and Henry 1970; Hairston 1987). These two species replace each other over an elevational gradient (Highton and Henry 1970; Hairston 1987). Hybridization occurs between them along the borders of all isolates of P. shermani, to such an extent that the areas between the P. shermani Standing Indian, Tusquitee, and Wayah isolates contain hybrid swarms (Highton and Henry 1970; Hairston 1987).
Other species with which P. shermani hybridizes include P. aureolus and P. chattahoochee. Hybridization has been found to occur between P. shermani and P. aureolus in the northern portion of the P. shermani Unicoi isolate (Highton 1983; Highton and Peabody 2000). P. shermani hybridizes with P. chattahoochee in the southern part of the Standing Indian isolate (Highton and Peabody 2000).
This species was featured as News of the Week on 16 November 2020:
To improve predictions for how species will respond to our changing climate, we should not neglect the behavioral consequences of climate change. Gade et al. (2020) set out to address this shortcoming: they wanted to project how the changing conditions of the next century will influence salamander surface activity. They conducted surveys of three species of the Plethodon jordani complex in the Appalachians of the US, identified predictors of salamander surface activity and abundance (temperature and water vapor pressure), then used this relationship to explore how the surface activity of P. jordani complex species will respond to stabilization and high emissions climate scenarios. They found that the probability of salamander surface activity during peak active season increased over time, though gladly temperatures were not predicted to surpass the species' thermal maxima. Surface activity is important to salamanders because it their opportunity to forage and mate, so this outcome may sound like good news. However, the authors qualify that there are physiological trade-offs at play, so modified behavioral patterns can have unpredictable consequences. For example, higher temperatures increase metabolism and may decrease the energy assimilation of salamanders, which can result in smaller body sizes and lower growth rates, and in turn, result in delayed sexual maturity and lower fecundity. The authors show how the examination of behavior like surface activity, critical to their fitness, can reshape our understanding of how species will fare with a changing climate (Written by Emma Steigerwald).
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