Description
Pristimantis gretathunbergae is a dark-eyed frog described from eight males and three females. It has a snout to vent length range of 26.5 to 36.7 millimeters in males and 38.15 to 46.3 millimeters in females. The head width is similar to the head length in both males and females. When viewed from above, the snout is short, broad, and round. When viewed from the side, the snout slightly projects outward. The upper eyelid, which is larger than the interorbital distance, has a single conical tubercle whose shape can range from spine-like to triangular. The tympanic membrane is completely concealed in females, but slightly exposed in males. The vocal slits in males are absent. The tympanic fold originates from the posterior end of the eye to where the arm is attached to the body. The dorsal skin is shagreen with scattered tubercles, while the ventral is slightly areolate. There are no dorsolateral folds, but the discoidal folds are present. The cloaca is smooth anteriorly but granular posteriorly. The frog exhibits 4 - 5 low ulnar tubercles and the hands are about 30% of the snout-vent length. The low thenar tubercle is long and there are additional weak palmar and supernumeary tubercles present. The fingers exhibit narrow lateral fringes, however, they have no webbing and nuptial pads are absent in male frogs. The relative finger lengths are I < II < IV < III with the fingertips of II - IV expanded into truncated discs. The subarticular tubercles are rounded and elevated in the lateral view. The hind limbs are about half the length of the snout-vent length. The heel of the frog’s foot has conical tubercles. There is no tarsal ridge. The inner metatarsal tubercle is elongated and larger than the somewhat pointed outer metatarsal tubercle. There are few supernumerary plantar tubercles. The toes have lateral fringes that are narrow, but no webbing between the toes. The relative toe lengths are I < II < III < V < IV and the toes tips are broadly expanded. The conical subarticular tubercles are not protuberant with one found on the first and second toes, two on the third and fifth toes, and and three on the fourth toe (Mebert et al. 2022).

DIAGNOSIS:

Pristimantis gretathunbergae differs from other Pristimantis species of rain frogs throughout eastern and central Panama by multiple morphological characteristics. For example, P. gretathunbergae lacks nuptial pads and vocal slits. Moreover, the eyes of P. gretathubergae have non-reticulated irises that are dark brown to black in color, whereas other rain frog species have irises that are pale or contain heavy flecking. The most comparable Pristimantis species is P. cruentus, as it has a similar body size to P. gretathunbergae. They can be differentiated mainly by head characteristics. Pristimantis cruentus has a longer trunk, a wider head, a partially visible tympanum in female, larger eyes and eyelid width, a variable number of tubercles (vs. only one) on the upper eyelid, and light-colored irises that are reticulated, while P. gretathunbergae has very dark colored irises without any reticulation. However, there sometimes are small golden or reddish flecks in P. gretathunbergae irises as well. Furthermore, the upper lip in P. gretathunbergae has a light coloration that is starkly contrasted to a dark color that is on the snout above. This is different from P. cruentus, who does not have a contrasted lip coloration and instead has a diffused edge with the darker upper snout coloration. Other color differences can be used to differentiate the two species. For example, P. gretathunbergae has a reddish or whitish yellow venter, which is occasionally spotted, while P. cruentus ranges from a mottling of black and white to being heavily black and white. Dorsally, P. cruentus is a gray, brown, or brownish black color, in contrast, P. gretathunbergae usually has more of a yellowish- or reddish-brown colored dorsum that can also be a light gray color (Mebert et al. 2022).

Pristimantis gretathunbergae also differs from other species in the Pristimantis ridens group through its larger size and white, cream, yellow, or even orange-red colored inguinal area. Other closely related species have a general brown dorsal coloration and also have distinct tympanic membranes in comparison to P. gretathunbergae’s lack of visible tympanum. More specific differences include that P. caryophyllaceus has a smooth skinned dosum that is slightly covered in tubercles and has a sharp snout that projects outward. Pristimantis gaigai has orange dorsolateral stripes with black coloration. Pristimantis moro and P. museosus have a green dorsum. Pristimantis pardalis has white spots on the anterior and lateral parts of its thighs. Pristimantis erythropleura live in similar habitats as P. gretathunbergae, but has a smaller body size, red to gold eyes with reticulation, and nuptial pads on males. Pristimantis penelopus and P. sanguineus have a more visible tympanum and a venter that is orange to cream colored with specking of brown. The only other Pristimantis species that have black eyes from northwestern South America are P. arcerus, P. farisorum, P. orcesi, P. parectatus, and P. piceus. However, they are species that primarily occupy elevations of 2000 meters or more in the Andean Mountains, which is not within the same range as P. gretathunbergae (Mebert et al. 2022).

COLORATION:

In life, the dorsum has a cream color background and large irregular reddish blotches, which do not extend to the flanks. The upper lip margin is contrasted with the darker snout coloring. Some males may have blotches that spread above the lip margin. The iris is nearly black and may have reddish gold speckles. Transverse bars are present on the thighs and anterior section of the tibia and foot. The top surface of the groin is reddish colored while the bottom is yellow. The venter is dirty white, and the area between the flanks is cream colored. In preservative, the dorsum is cream colored, with small dark pigmentations. The groin, hind limbs and forelimbs are pale with the dark transverse bands being less clear than in life. Moreover, the ventral area is cream colored, and the underparts of digits have dark scattered dark pigmentation (Mebert et al. 2022).

VARIATION:

Most specimens of P. gretathunbergae follow the general description, however, there is variation in the coloration of the dorsal and ventral surfaces. While the dorsum is generally pale brown, it may also contain yellow to red pigmentation, scattered orange flecking, large red or distinct brown blotches, or a light dorsolateral band. The venter may have some dark spotting as well between specimens. A prominent light upper lip is existent in all female specimens, but only some males display this feature, while others exhibit some blotching vertically on the lip, stemming from the snout. Another large aspect of variation lies in the size of the frog, as females are much larger than male specimens. Females are also relatively wider and have less exposed tympanums than males (Mebert et al. 2022).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Panama

View distribution map in BerkeleyMapper.

Pristimantis gretathunbergae resides in Panama but has also been found near the mountains bordering Colombia. It is most prevalent throughout eastern Panama and into the central region with recorded sightings in the Darien and Maje Mountains. The species has been known to occupy elevations of 718 m to 1439 m and mostly resides in montane forest (Mebert et al. 2022).

Life History, Abundance, Activity, and Special Behaviors
Pristimantis gretathunbergae individuals have been observed on bromeliad leaves around mid-day. During the rainy season, in December, males were heard calling at Cerro Chucantí and three females were found protecting a clutch of eggs for four nights. This occurred in the mossy trees and bromeliads near Gaira hills (García-R et al., 2015; Mebert et al., 2022).

The exact diet of the species is unknown, however, it is likely that they feed on arthropods such as ants, spiders, and orthopterans likewise to the diet of other Pristimantis species (Mebert et al. 2022).

Trends and Threats
Pristimantis gretathunbergae has a declining population due to anthropogenic pressure stemming from habitat loss associated with agriculture and disease related to the chytrid fungus Batrachochytrium dendrobatidis. Pristimantis gretathunbergae should be listed as “Vulnerable,” in the IUCN Red List, based on the criteria for reduced area occupancy, and fragmented range. For example, the Maje and Cerro Chucantí Mountains are areas of concern for this species. Moreover, due to its high Environmental Vulnerability Score of 18, the species is listed in the upper segment of high vulnerability categories (Batista et al. 2020, Mebert et al. 2022, Voyles et al. 2018)

Possible reasons for amphibian decline

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

Comments

PHYLOGENETIC RELATIONSHIPS:

Maximum Likelihood and Bayesian methods on 16S and COI mtDNA showed that Pristimantis gretathunbergae is most closely related to P. cruentus. The next most closely related clade is composed of P. penelopus, and P. erythropleura, which are western Colombia species (Mebert et al. 2022).

ETYMOLOGY:

The species epithet, “gretathunbergae” is in honor of Greta Thunberg who is a Swedish student known for her climate activism. Greta Thunberg encouraged students worldwide to advocate for action by the government to advert the dire consequences of climate change. She has organized many protests and strikes at climate talks and conferences to bring change to the status quo (Mebert et al. 2022).

OTHER INTERESTING INFORMATION:

Pristimantis gretathunbergae, was previously listed as P. aff. latidiscus on GenBank until it was revealed that the group had a large genetic divergence, greater than 11%, to P. latidiscus, which can be found in Ecuador (Merbert et al. 2022)

References
Batista, A., Mebert, K., Miranda, M., Garces, O., Fuentes Magallón, R., Ponce, M. (2020). Endemism on a threatened sky island: New and rare species of herpetofauna from Cerro Chucantí, Eastern Panama. Amphibian and Reptile Conservation, 14, 27–46. [link]

García-R, J., Carmen, P., Cárdenas, H. (2015). Diet of direct-developing frogs (Anura: Craugastoridae: Pristimantis) from the Andes of western Colombia. Acta Biológica Colombiana, 20, 79–87. [link]

Mebert K., González-Pinzón M., Miranda M., Griffith E., Vesely M., Schmid P.L., Batista A. (2022). A new rainfrog of the genus Pristimantis (Anura, Brachycephaloidea) from central and eastern Panama.” ZooKeys 1081: 1–34. [link]

Voyles, J., Woodhams, D. C., Saenz, V., Byrne, A. Q., Perez, R., Rios-Sotelo, G., Ryan, M. J., Bletz, M. C., Sobell, F. A., McLetchie, S., Reinert, L., Rosenblum, E. B., Rollins-Smith, L. A., Ibáñez, R., Ray, J. M., Griffith, E. J., Ross, H., Richards-Zawacki, C. L. (2018). Shifts in disease dynamics in a tropical amphibian assemblage are not due to pathogen attenuation. Science, 359(6383), 1517– 1519. [link]

Species Account Citation: AmphibiaWeb 2023 Pristimantis gretathunbergae: Greta Thunberg’s Rainfrog <https://amphibiaweb.org/species/9484> University of California, Berkeley, CA, USA. Accessed Oct 1, 2023.

Citation: AmphibiaWeb. 2023. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 1 Oct 2023.

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