Description
Pristimantis mutabilis is a relatively small species of frog with a snout-vent length of 17.2 – 17.4 mm in males, and 20.9 – 23.2 mm in females. The head is a bit longer than it is wide, though narrower than the width of its body. There is a single conical tubercle on each upper eyelid, as well as several low tubercles. The snout appears rounded when viewed from the sides and the back. The eye diameter is larger than the distance between the eye and the nostril. The nostrils do not protrude, and are positioned towards the front and sides of the body. The canthus rostralis is curved slightly inwards, as is the region between the eye and nostril. The tympanum is well defined except for the upper side, which is covered by a supratympanic fold. There are two postrictal tubercles positioned towards the behind and under the tympanum. The skin on the back is coarse and punctuated with tubercles, though it has the ability to become smooth in life. There are dorsolateral folds present on its back, and the underside is warty in texture. Two ulnar tubercles are present, as well as a large outer palmar tubercle split in two. The subarticular tubercles are distinct and circular, and the supernumerary tubercles are present though few in number. The fingers have fine lateral fringes. Finger I is shorter than Finger II, but no other information is available on relative finger lengths. The fingertips are noticeably ovoid and enlarged, though less so in Finger I. The undersides of the hands have pads that are surrounded by grooves. The heel tubercle is conical, and the tarsal tubercles and minute and indistinct. The inner metatarsal tubercle is ovoid and twice as big as the circular outer metatarsal tubercle. The subarticular tubercles are also circular, and the supernumerary tubercles are faint. The toes have fine lateral fringes, and lack webbing. The toe tips are grooved. The relative toe lengths are: I < II < III < V < IV (Guayasamin et al. 2015).

This species is easily diagnosed in life as it has the ability to interchange its skin texture from tuberculate to smooth, which is a trait found in only one other frog species, P. sobetes. In preservative, it can be diagnosed from a combination of the following characters: coarse skin punctuated with tubercles; presence of dorsolateral folds; tympanum present and partially covered on top by a supratympanic fold; smooth truncate snout; conical tubercle present on upper eyelid; vocal sac in males; no nuptial pads in males; Finger I shorter than Finger II; lateral fringes on fingers and toes; conical tubercle on heel; no toe webbing; Toe V longer than Toe III; enlarged circular toe tips. It is similar in appearance to P. verecundus, though P. verecundus differs in having short dorsolateral folds that don’t extend past the sacrum (versus long dorsolateral folds that extend past the sacrum in P. mutabilis), a V shape on the throat of females, and the slightly larger size in males. It is similar in appearance to P. sobetes and shares the ability to change its skin texture, though P. sobetes differs in males being significantly larger than the females, having a bright red iris with no stripe (versus a light old iris with a red stripe in P. mutabilis), and lacking red flash coloration near the vent or the underside of the thighs (Guayasamin et al. 2015).

In life, the back is light brown to grey green, with bright green markings and grey or brown V shaped patterns that are bordered by a fine white line. The dorsolateral folds are orange. The underside is light grey to brown and has darker spots, as well as some smaller white spots. The iris is creamy to golden and has a fine black netted pattern as well as a red horizontal streak. The underside of the thighs and the groin is red. In preservative, it has a light brown to grey back, with dark V shaped patterns that are bordered by a fine white line. The dorsolateral folds are light pink. There are dark diagonal stripes on the limbs and sides of the body (Guayasamin et al. 2015).

The skin texture is highly variable in live specimens, as this species is able to change its skin from tuberculate to smooth depending on conditions in its environment (Guayasamin et al. 2015).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Ecuador

View distribution map in BerkeleyMapper.

It occurs in northwestern Ecuador, within primary and secondary forests in the Andes mountain range. Specifically, it has been found at Reserva Las Gralarias in Pichincha province, and at Reserva Los Cedros in Imbabura province. It has an altitudinal range of 1850 – 1880 m asl (Guayasamin et al. 2015).

Life History, Abundance, Activity, and Special Behaviors
This species has been found hiding in moss or perched on leaf surfacts at least one meter above the ground. All individuals were initially found with the tuberculate skin texture, though they would change the texture to smooth upon capture, and revert to a tuberculate texture once returned to their environment. It is possible that stress, humidity, and background are responsible for the change in skin texture. The function of this is unknown, though it may be for the purposes of camouflage to hide from predators. The exact physiological mechanism of this texture change has not been studied, though it is possible that it involves water movement in and out of structures in its skin (Guayasamin et al. 2015).

Males were heard calling during January and February 2013. Three distinct calls are made. The first type was a single note that sounded like a short ring and is composed of one modulated pulse with a robust amplitude and 2 - 4 modulated pulse with weak amplitudes. The call does not have frequency modulation and has a pulse rate of 0.041 - 0.11 pulses per ms, a call duration is 45.7 - 49.0 ms, and a dominate frequency between 3273 - 3359 Hz. The limits of the fundamental frequency are 3255 - 3346 Hz for the lower limit and 3617 - 3708 Hz for the upper limit (Guayasamin et al. 2015).

The second type consisted of a single screech-like pulsed note composed of two or more robust and many weak amplitude modulated pulses. This call also is not frequency modulated and has a pulse rate of 0.138 - 0.274 pulses per ms, a duration of 68.0 - 99.0 ms, and a dominate frequency of 3358 - 3445 Hz. The limits of The limits of the fundamental frequency are 3256 - 3345 Hz for the lower limit and 3708 - 3799 Hz for the upper limit (Guayasamin et al. 2015).

The third type consisted of a series of 5 – 6 long trill-like calls broken by short intervals between each and increasing in frequency with each successive call. The duration of the series of calls is 301.0 - 456.0 ms with a 4.2 - 7.3 second interval between series. Individual calls have a single robust modulated pulse and many weaker ones, similar to call type 1. This type of call has a pulse rate of 0.055 - 0.089 pulses per ms and a dominate frequency of 3187 - 3445 Hz, which can modulate by an increase of 87 - 173 Hz. The limits of the fundamental frequency are 3165 - 3346 Hz for the lower limit and 3708 - 3799 Hz for the upper limit (Guayasamin et al. 2015).

Trends and Threats
It is presumed to be abundant in the localities where it was found, as males are frequently heard calling at night. More research needs to be conducted to determine the population trends for this species (Guayasamin et al. 2015).

Comments
The species authority is: Guayasamin, J. M., Krynak, T., Krynak, K., Culebras, J., Hutter, C. R. (2015). "Phenotypic plasticity raises questions for taxonomically important traits: a remarkable new Andean rainfrog (Pristimantis) with the ability to change skin texture." Zoological Journal of the Linnean Society, 173, 913-928.

Based on Maximum Likelihood and Bayesian analysis from combined 12S and 16S genetic sequence data, it is placed in the P. myersi species group (which includes P. leoni, P. trepidotus, P. pyrrhomerus, P. ocreatus, P. thymelensis, P. hectus, P. jubatus, P. celator, P. mutabilis, and P. verecundus). Though it shares the otherwise unique ability to immediately change its skin texture with P. sobetes, genetic evidence shows that the two species are distantly related, with P. sobetes being place in the P. surdus species group (Guayasamin et al. 2015).

Only P. mutabilis and P. sobetes are known to change its skin texture. However, as the two species are not closely related within Pristimantis, it is possible that this trait evolved independently in both species, or that other Pristimantis species too share this trait but have not yet been documented to demonstrate it. Another possibility is that this trait was expressed in the common ancestor of the P. myersi and P. surdus groups, but only retained in P. mutabilis and P. sobetes (Guayasamin et al. 2015).

The specific epithet mutabilis is Latin for the ability to change, in reference to this frog’s ability to change the texture of its skin (Guayasamin et al. 2015).

References

Guayasamin, J. M., Krynak, T., Krynak, K., Culebras, J., Hutter, C. R. (2015). ''Phenotypic plasticity raises questions for taxonomically important traits: a remarkable new Andean rainfrog (Pristimantis) with the ability to change skin texture.'' Zoological Journal of the Linnean Society, 173, 913-928.

Species Account Citation: AmphibiaWeb 2015 Pristimantis mutabilis: Mutable Rainfrog <https://amphibiaweb.org/species/8315> 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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