Blacksburg Salamander

Blacksburg Salamander
Plethodon jacksoni

Common Name:	Blacksburg Salamander
Scientific Name:	Plethdon jacksoni
Etymology:
Genus:	plethore is Greek meaning "fullness or full of", odon is Greek for "teeth". Referring to the number of paravomerine and vomerine teeth.
Species:	jacksoni The species is named after a former Associate Professor of Biology at Virginia Polytechnic Institute known as Dr. Herbert W, Jackson. He was crucial in collecting within Southwestern Virginia, and thus generated interest from a multitude of herpetologists.
Average Length:	69 - 135 mm (average 116.1 mm (4.6 in.)) in adult males and 113 - 133 mm (average 124.6 mm (4.9 in.) in adult females
Virginia Record Length:	?
Record length:	?

Physical Description - Plethodon jacksoni is a large, slender Plethodon from the eastern United States that has a similar morphology to Plethodon wehrlei and Plethodon dixi, but has an intermediate total length of range 69 - 135 mm (average 116.1 mm) in adult males and 113 - 133 mm (average 124.6 mm) in adult females. Newman (1954) identified one small specimen with a snout-vent length of 17 mm and a total length of 27 mm, but it is unclear if this is a juvenile. From the dorsal view, the head shape of P. jacksoni is broadly oval with its widest point immediately posterior to its eyes. The snout is depressed and bluntly pointed. Plethodon jacksoni has 4 vomerine teeth and 6 - 7 parasphenoid teeth shared between two slender patches that are separated from the vomers approximately the diameter of the salamander’s naris. The teeth are slightly wider towards the posterior. The mental glands of the male are obvious. There are also noticeable swellings in males below each naris that projects downward. The eyes are prominent. The well-rounded body is slightly wider than tall at their largest points. Between the axilla and groin, there are 15 - 18 costal grooves in total, including the grooves in the axilla and groin, and 3 - 4 intercostal grooves. The vent is somewhat protuberant (Newman 1954).

Though originally categorized with P. wehrlei and P. dixi, P. jacksoni can be distinguished from these two species based on the following characteristics: red spotting found on the dorsum of adults, and sexually mature males possess unique mental glands and hedonic swelling located at the base of the tail. Additionally, the ventrum displays distinct color and distribution of the light and dark areas. The dorsal red spotting is considered rare or absent in P. wehrlei. The red spots can range from faint to conspicuous and vary in number for each individual. Other than the red spotting, P. jacksoni may appear as either P. wehrlei or P. dixi due to the extent of side markings the individual have. Some have been found with light markings fully encroaching on the belly, giving a heavily mottled effect like in P. dixi. Others have been found with the light markings only on the outer margins like in P. wehrlei. However, this variation has been found only in a few specimens, both with and without the red spotting (Newman 1954). Red spotting, rather than yellow, also differentiates P. jacksoni from P. pauleyi. Additionally, the yellow spots in P. pauleyi are in loose pairs starting at or posterior to the insertion of the forelimbs to just posterior of the hind limbs while the red spots in P. jacksoni are scattered randomly (Felix et al. 2019).

In life, P. jacksoni has a deep slaty-blue or blueish-black dorsum with white flecks in moderate to high abundance. A silvery mottling extends along its back and tail but is absent or faintly marked on the head. Along the cheeks and lower flanks, P. jacksoni has a lateral marking that is continuous to a point opposite of the posterior angle of the vent. This marking is usually a shade lighter than the dorsal ground color. The lower third of the flanks has moderate to heavy white blotches either fully reaching the belly or more commonly, leaving the mid-ventral dark. The limbs are mottled similarly to the flanks. The belly matches closely to the ground of its habitat. Typically, the chest is lighter in color with a few darker areas, throat is lighter than belly and mottled with small lighter areas (Newman 1954).

After preservation in formalin, the dorsal coloration becomes more of a deep brownish black, losing the blue coloration P. jacksoni has in life. The head and posterior portion of the tail also becomes slightly more brownish after becoming preserved. The distinct dorsal red spotting becomes yellowish white. Silver mottling along the body fades and mostly disappear within twenty-four hours. The light flecks remain evenly distributed on the head and back, but less evident on the posterior portion of the tail. The belly color fades to a very light gray (Newman 1954).

Plethodon jacksoni varies in number of costal and intercostal grooves, vomerine tooth counts, and coloring and patterning. Additionally, the species exhibits sexual dimorphism. While the average number of costal grooves in the species description was between 16 - 17, outliers included 15 and 18 costal groove counts. Intercostal groove counts were between 3 - 4. Vomerine tooth counts from the right and left series ran a gamut between 9 to 15. There are many variations in markings across individuals. The throat and chest may vary extremely in the amount of dark and light areas. Individuals vary from heavily to sparsely mottling. There seems to be no association between mottling and darkened areas as a number of specimens have a light throat and mottled chest, yet others have a mottled throat and light chest. In rare instances, the white dorsal flecks may also extend onto the belly. In this species, there is no indication of correlation between markings, sex, or dorsal spotting. Sexual dimorphism is present in this species with males possessing protuberant mental glands and swelling extending below each naris. Furthermore, large males may possess a hedonic swelling above the base of the tail. Compared to females who have 4 intercostal grooves between adpressed limbs, males tend to have relatively shorter bodies with approximately half of males having 3 grooves between adpressed limbs (Newman 1954).

Trends and Threats: In 2018, P. jacksoni was listed as “Critically Imperiled” in North Carolina (Felix et al. 2019). The species has yet to be evaluated by the IUCN Red List.

Possible reasons for amphibian decline: General habitat alteration and loss Habitat modification from deforestation, or logging related activities.

Comments:

The species authority is: Newman, W. B. (1954). “A new plethodontid salamander from southwestern Virginia.” Herpetologica, 10, 9–14.
Bayesian inference of CytB and Maximum Likelihood of whole genome scale loci both indicate that P. jacksoni is sister to the clade composed of P. pauleyi, P. punctatus and P. wehrlei. Together, this clade is sister to P. dixi. There may be more species, with P. jacksoni being split into two species, but a more detailed geographic survey is needed (Felix et al 2019).
The species is named after a former Associate Professor of Biology at Virginia Polytechnic Institute known as Dr. Herbert W, Jackson. He was crucial in collecting within Southwestern Virginia, and thus generated interest from a multitude of herpetologists. Moreover, Newman notes that he was a source of support for many aspiring naturalists (Newman 1954).
Plethodon jacksoni was described by Newman in 1954 based on morphology but was later synonymized with P. wehrlei by Highton in 1962. Highton later suggested the species’ genetic distinctiveness in 2012. Kuchta et al. (2018) analyzed the genetic structure of the P. wehrlei complex and found modest support for P. jacksoni being a full species. However, it was Felix et al. (2019) was who formally elevated P. jacksoni back to a full species.

References for Life History

AmphibiaWeb 2020 Plethodon jacksoni: Blacksburg Salamander University of California, Berkeley, CA, USA
Dodd, C. (1989). ''Duration of immobility in salamanders, genus Plethodon (Caudata: Plethodontidae).'' Herpetologica, 45(4), 467- 473.
Felix, Z., Wooton, J. A., Pierson, T. W., Camp, C.D. (2019). ''Re-evaluation of the Wehrle’s salamander (Plethodon wehrlei Fowler and Dunn) species group (Caudata: Plethodontidae) using genomic data, with the description of a new species.'' Zootaxa, 4609(3), 429-448.
Hall, R., Stafford, D. (1972). ''Studies in the life history of Wehrle's salamanders, Plethodon wehrlei.'' Herpetologica, 28(4), 300-309.
Kuchta, S.R., Brown, A.D., Highton, R. (2018). ''Disintegrating over space and time: paraphyly and species delimitation in the Wehrle’s salamander complex.'' Zoologica, 47, 285–299.
Newman, W. B. (1954). ''A new plethodontid salamander from southwestern Virginia.'' Herpetologica, 10(1), 9–14.
Palmer, C. A., Watts R. A., Gregg, R. G., McCall, M. A., Houck, L. D., Highton R., Arnold S. J. (2005). ''Lineage-specific differences in evolutionary mode in a salamander courtship pheromone.'' Molecular Biology and Evolution, 22(11), 2243-2256.

Photos:

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