Description
Thorius pinicola is a long, slender-bodied salamander with a mean snout-vent length of 23.5 - 29.6 mm in males and 25.5 - 28.2 mm in females. The head length is more than the head width. They have relatively large, elliptical-shaped nostrils. Their limbs are relatively small compared to body size, but their tail is long. They have no maxillary teeth (Parra-Olea et al. 2016). For more on their description please see Parra-Olea et al. 2016

DIAGNOSIS:

The genus Thorius is considered to be easy to identify compared to other genera because of their characteristically small size. However, differentiating species within this genus is difficult and has only recently become possible due to advancements in molecular methods. Thorius pinicola is relatively large, which differentiates it from T. arboreus, T. insperatus, T. minutissimus, T. papaloae and T. smithi. In addition to being larger than the similar T. minutissimus, a species found in a similar range, T. pinicola has a longer tail. Additionally, although both species are found in the Sierra Madre del Sur of Oaxaca, Mexico, T. pinicola has more of a western range. Thorius pinicola can mostly be differentiated from T. longicaudus and T. tlaxiacus by molecular data. However, the nostril shape is more elliptical in T. pinicola than in T. tlaxicaus and there are fewer vomerine teeth in T. pinicola than in T. longicaudus. Otherwise, they are superficially similar and difficult to differentiate by eye (Parra-Olea et al. 2016).

COLORATION:

In life, T. pinicola is usually uniformly dark brownish-gray in coloration. It typically has stripes of slightly lighter and darker hues running along the length of its body on either flank. It may have fine, light speckling across the body. In preservative, if any markings are visible, they are usually paler than less distinctive than in living specimens (Parra-Olea et al. 2016).

VARIATION:

Based on data collected from eight male and nine female specimens, there is no significant sexual dimorphism in T. pinicola (Parra-Olea et al. 2016).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Mexico

View distribution map in BerkeleyMapper.

The distribution of T. pinicola is very small since they are only found in the Southern part of Mexico, in the State of Oaxaca in the Miahuatlán District. The upper elevation limit is around 3,000 meters and the lower elevation limit is 2,490 meters. Their habitat type is between temperate and subtropical forests. They are most commonly found in pine-cone forest, normally under logs or other vegetation that allows them to hide and protect themselves (Parra-Olea et al. 2016, IUCN 2022).

Life History, Abundance, Activity, and Special Behaviors

During the initial collection of T. pinicola, specimens were observed living under fallen trees or underneath the bark of dead logs, where moisture was trapped. It is noted that the layer of pine needles covering the ground prevented moisture from reaching the soil below, causing this area to be unsuitable as salamander habitat (Parra-Olea et al. 2016).

While reproduction has not been observed in T. pinicola, it is expected that the species is oviparous and produces offspring through direct development like other Thorius species (Parra-Olea et al. 2016). This form of development allows offspring to bypass their larval stage and emerge from their eggs in their terrestrial morph.

As members of Family Plethodontidae, T. pinicola are thought to reproduce through internal fertilization. Many members of this family utilize a courtship dance called the “tail-straddle walk” to position the female’s cloaca over the spermatophore deposited by the male (Arnold et al. 2017). In addition to performing a courtship dance, males can release pheromones, which are received through the naso-labial grooves of the female during the courtship process.

Although the species lacks information about their natural predators, the presence of a parotoid gland, a gland that produces alkaloid substances in amphibians, and tibial spurs indicates they have anti-predator defenses. Despite having these apparent defenses, T. pinicola’s cryptic coloration appears to be their primary feature to avoid predator detection (Parra-Olea et al. 2016).

Trends and Threats
Thorius pinicola is listed as “Endangered” by the IUCN Red List of Threatened Species because it has a small estimated extent of occurrence (EOO) of 121 Km squared, which is declining in quality of habitats. Additionally, the entire T. pinicola population comprises approximately 2,500 individuals with the population maintaining a downward trend since the 1980s. Some of the common threats to this species are logging, wood harvesting, agriculture and aquaculture, and invasive diseases (IUCN 2020).

More specifically, logging of pine forests around Rio Copalita (Copalita River) has contributed to desiccating conditions of salamander habitat. The build up of fallen logs and pine needles has created a barrier preventing moisture from reaching the soil, reducing the amount of viable habitat available for T. pinicola (Parra-Olea 2016).

Chytrid fungus, Batrachochytrium dendrobatidis, has spread across North America and has left amphibians vulnerable to developing chytridiomycosis. According to Cornell Wildlife Health Lab, chytridiomycosis causes skin lesions which can inhibit cutaneous oxygen exchange and limit hydration uptake (“Chytridiomycosis” 2018). Without treatment, this disease can become fatal. As lungless salamanders, T. pinicola relies entirely on cutaneous respiration for oxygen exchange making the species particularly vulnerable to chytrid fungus infection. In addition to B. dendrobatidis, the closely related fungus, Batrachochytrium salamandrivorans, has been identified as a potential threat for amphibians living in high altitudes, including T. pinicola (IUCN 2020). While B. salamandrivorans has not reached North America, the risk of invasion has been identified as a conservation threat to lungless salamanders (Carter et al. 2019).

All specimens used to identify T. longicaudus, T. pinicola, and T. tlaxiacus, which were described together, were collected over 35 years ago. They also all have had dramatic population declines that have made the collection of new specimens nearly impossible and are at serious threat of extinction (Parra-Olea et al. 2016).

Relation to Humans
There is no evidence of them having a relation to humans since they are not easily found and are mostly hidden under logs or other hiding places the majority of time.

Possible reasons for amphibian decline

General habitat alteration and loss
Habitat modification from deforestation, or logging related activities
Intensified agriculture or grazing
Disease

Comments

PHYLOGENETIC RELATIONSHIPS:

Maximum Likelihood and Bayesian analyses of 16S, cytB, and ND4 mtDNA, and Rag1 nDNA, found that T. pinicola is most closely related to the clade composed of T. grandis, T. omiltemi and T. tlaxiacus. The next most closely related species is T. longicaudus (Rovito et al. 2013). However, none of the species in Rovitio et al. (2013) were named until the 2016 Parra-Olea study, which formally separated them from T. minutissimus (Parra-Olea et al. 2016).

ETYMOLOGY:

The species epithet, “pinicola” is derived from the Latin words “pinus”, meaning “pine”, and the suffix “-cola”, meaning “inhabitant of”. This is a reference to T. pinicola’s habitat of pine vegetation (Parra-Olea et al. 2016).

References

Arnold, S., Kiemnec-Tyburczy, K., Houck, L. (2017). "The evolution of courtship behavior in Plethodontid salamanders, contrasting patterns of stasis and diversification." Herpetologica, 73(3), 190-205. [link]

Carter, E.D., Miller, D.L., Peterson, A.C., Sutton, W.B., Cusaac, J.P.W., Spatz, J.A., Rollins-Smith, L., Reinert, L., Bohanon, M., Williams, L.A., Upchurch, A., Gray, M.J. (2019). "Conservation risk of Batrachochytrium salamandrivorans to endemic lungless salamanders." Conservation Letters 13(1), e12675 [link]

IUCN SSC Amphibian Specialist Group. (2020). "Thorius pinicola." The IUCN Red List of Threatened Species 2020: e.T119243850A119243854. https://dx.doi.org/10.2305/IUCN.UK.2020-3.RLTS.T119243850A119243854.en. Accessed on 22 February 2022.

Parra-Olea, G., Rovito, S.M., García-París, M., Maisano, J.A., Wake, D.B., Hanken, J. (2016) “Biology of tiny animals: three new species of minute salamanders (Plethodontidae: Thorius) from Oaxaca, Mexico.” PeerJ 4:e2694 [link]

Rovito, S. M., Parra-Olea, G., Hanken, J., Bonett, R. M., Wake, D. B. (2013). ''Adaptive radiation in miniature: the minute salamanders of the Mexican highlands (Amphibia: Plethodontidae: Thorius).'' Biological Journal of the Linnean Society, 109, 622-643.

“Chytridiomycosis.” (2018). Cornell Wildlife Health Lab, Cornell University, https://cwhl.vet.cornell.edu/disease/chytridiomycosis. Accessed in February 2022

Species Account Citation: AmphibiaWeb 2022 Thorius pinicola: Pine-dwelling Minute Salamander <https://amphibiaweb.org/species/8529> University of California, Berkeley, CA, USA. Accessed Mar 30, 2023.

Citation: AmphibiaWeb. 2023. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 30 Mar 2023.

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