Description
Thorius tlaxiacus is one of the largest salamanders of its genus, with both males and females reaching up to 28 millimeters in standard length and their tails sometimes surpassing that length. They have “extremely distorted” nostrils. They have no maxillary teeth, but males have 4 - 6 vomerine teeth while females have 4 - 8. They have moderately short limbs in comparison with their larger body (Parra-Olea et al. 2016).

DIAGNOSIS:

Thorius tlaxiacus is larger than most other members of its genus. Another way they differ from species in the genus is that they have more “extremely distorted” nostrils than similar species, only sharing that trait with T. pulmonaris (Parra-Olea et al. 2016).

COLORATION:

In life, T. tlaxiacus has an extremely dark brown background color on their head, body, and tail, with minute white speckling all over the lateral regions, most notably on their neck and forelimb insertions. The speckling continues on to their gray abdomens, but is less concentrated than the previously mentioned areas. This species also has a prominent dark-brown dorsal stripe that branches off of a chestnut-colored spot on the back of their neck and reaches down to their mid-tail (Parra-Olea et al. 2016).

In preservative, T. tlaxiacus is similarly colored as it is in life, but is slightly lighter in all-over color. The spot at the beginning of their prominent dorsal stripe is golden, not chestnut-colored and meets up with chevron markings halfway down its length (Parra-Olea et al. 2016).

VARIATION:

Adult male and female T. tlaxiacus are similar in body size and head width, with males of the species being slightly larger on average by a margin of 0.3 mm for both factors. Males also have a distinct, large mental gland and more premaxillary teeth than their female counterparts. On the other hand, female T. tlaxiacus have more vomerine teeth, more costal grooves between adpressed limbs, and a slightly larger standard length to tail length ratio (Parra-Olea et al. 2016).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Mexico

View distribution map in BerkeleyMapper.

Thorius tlaxiacus is found in two regions of Oaxaca, Mexico - near Heroica Ciudad de Tlaxiaco and the village of San Vicente Lachixio in temperate, pine-oak forests. The former has a more variable elevation range of 2,665 to 3,080 meters while the latter has a range of 2,720 to 2,730 meters. These localities are approximately 80 km apart, and it is unknown if the salamander can be found between these localities (Parra-Olea et al. 2016).

Life History, Abundance, Activity, and Special Behaviors
Prior to 1999, T. tlaxiacus could be found in pine-oak forest in groups of 10 - 12 individuals in broken, fallen logs or as individuals under bark. However, the site where they were commonly found has since been cleared and only three individuals were found in 1999. In 2014, no individuals were found (Parra-Olea et al. 2016).

Thorius tlaxiacus shares its habitat with T. narisovalis in Heroica Ciudad de Tlaxiaco and T. longicaudus in San Vicente Lachixio. Pseudoeurycea cochranae and P. anitae can also be found in San Vincente Lachixio (Parra-Olea et al. 2016).

Like all plethodontid salamanders, T. tlaxiacus, breeds on land, in a process referred to as direct development (IUCN 2020). The salamanders hatch as miniature versions of the adult as opposed to going through a larval stage and then metamorphosing.

Trends and Threats
As of 2020, the IUCN has listed T. tlaxiacus as “Endangered” with its population trend described as decreasing. Since the 1980s the population has been declining and its habitat severely fragmented. The species was considered abundant in the 1980s, but only three were found after the area had wood extraction in 1999. Furthermore, no individuals were found during a 2014 survey. Fewer than 10,000 mature individuals of T. laxiacus are suspected to exist. The main threat is loss of its montane pine forest habitat, which is severely impacted by logging, and agriculture expansion. Due to their limited range, other possible contributors to the decline of this species include pesticide use in forest farming and climate change. There is also concern that the salamander chytrid fungus, Batrachochytrium salamandrivorans could have a large impact if it were to be introduced to Mexico (IUCN 2020).

Possible reasons for amphibian decline

General habitat alteration and loss
Habitat modification from deforestation, or logging related activities
Intensified agriculture or grazing
Local pesticides, fertilizers, and pollutants
Disease
Climate change, increased UVB or increased sensitivity to it, etc.

Comments

PHYLOGENETIC RELATIONSHIPS:

The phylogenetic relationships of Thorius is poorly resolved, however, analyses on mitochondrial and nuclear gene DNA sequences indicate that Oaxacan Thorius form a well-supported clade (Parra-Olea et al. 2016).

ETYMOLOGY: (Origin or explanation of scientific name):

The species epithet, “tlaxiacus” is a reference to where the holotype was found, Heroica Ciudad de Tlaxiaco. The city was also an important regional center during the colonial period of Mexico (Parra-Olea et al. 2016).

References

IUCN SSC Amphibian Specialist Group. (2020). "Thorius tlaxiacus." The IUCN Red List of Threatened Species 2020: e.T119243882A119243892. https://dx.doi.org/10.2305/IUCN.UK.2020-2.RLTS.T119243882A119243892.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]

Species Account Citation: AmphibiaWeb 2022 Thorius tlaxiacus: Heroic Minute Salamander <https://amphibiaweb.org/species/8531> University of California, Berkeley, CA, USA. Accessed Nov 21, 2024.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 21 Nov 2024.

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