Pristimantis mutabilis GUAYASAMIN, KRYNAK, KRYNAK, CULEBRAS, & HUTTER, 2015

Guayasamin, Juan M., Krynak, Tim, Krynak, Katherine, Culebras, Jaime & Hutter, Carl 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 (4), pp. 913-928 : 916-922

Pristimantis mutabilis GUAYASAMIN, KRYNAK, KRYNAK, CULEBRAS, & HUTTER , SP. NOV.

Common English name

Mutable Rainfrog.

Common Spanish name

Cutín Mutable.

Holotype ( Fig. 1 )

MZUTI 2190 , an adult male obtained by Juan M. Guayasamin on February 1, 2013, at Reserva Las Gralarias (00.00843° S, 78.7305° W; 2063 m.a.s.l.), Pichincha province, Ecuador.

Paratopotypes

MZUTI 2191 , sub-adult male with same data as holotype . MZUTI 413 , adult female collected by Carl R. Hutter on March 24, 2012, within Reserva Las Gralarias (‘Puma Trail’: 0.00954° S, 78.7346° W; 2030 m.a.s.l.) .

Referred specimens

MZUTI 909 (juvenile), 910–911, 913 (adult females), and 912 (adult male) were collected by Amanda Delgado, Jaime García, Fernando J. M. Rojas-Runjaic, Guissepe Gagliardi-Urrutia, Paloma Lima, and Juan M. Guayasamin, at Reserva Los Cedros (Sendero Oso: 0.3197 N, 78.7858 W, 1880 m; Sendero Cascada Nueva: 0.3249 N, 78.7809 W, 1850 m), Provincia Imbabura, Ecuador .

Generic and group placement

Pristimantis mutabilis is placed in the genus Pristimantis , as diagnosed by Hedges et al. (2008), because of the absence of cranial crests, and presence of dentigerous process of the vomers and T-shaped terminal phalanges. Within Pristimantis , the new species shares all traits that define the P. myersi group (sensu Hedges et al., 2008); these traits are: small body size (female SVL <28 mm), robust body, short snout and relatively narrow head, Finger I shorter than Finger II, Toe V slightly longer than Toe III, tympanic membrane differentiated, cranial crests absent, vomerine teeth present and, in adult males, vocal slits present. Furthermore, generic and group placement is strongly supported by genetic analyses (see below).

Diagnosis

We provide a diagnosis based on preserved specimens; however, we emphasize that this species presents a marked skin texture variation that cannot be observed on museum specimens and is described in the Variation of skin texture section. Pristimantis mutabilis was diagnosed by having:

1. skin texture of dorsum shagreen, with low interspersed tubercles; dorsolateral folds present, low; occipital fold usually present, but low; venter areolate;

2. tympanic membrane present; tympanic annulus barely visible, with upper rim obscured by supratympanic fold;

3. snout short, rounded in dorsal and lateral views;

4. upper eyelid with one conical or sub-conical tubercle and several low tubercles, which are almost unnoticeable in some specimens; cranial crests absent;

5. dentigerous process of vomers small, oblique in outline, positioned posterior to level of choanae, each process bearing 1–4 teeth;

6. males with small sub-gular vocal sac; vocal slits present; nuptial pads absent;

7. first finger shorter than the second; discs on fingers elliptical, laterally expanded ( Fig. 1 );

8. fingers bearing narrow lateral fringes; palmar tubercle bifurcated distally; few supernumerary tubercles present, round, fleshy ( Fig. 1 );

9. ulnar tubercles present, but difficult to distinguish in some specimens; inner tarsal fold absent;

10. heel with conical tubercle; tarsal tubercles present;

11. toes bearing narrow fringes; webbing absent; Toe V longer than Toe III; toe discs rounded and slightly expanded ( Fig. 1 );

12. inner metatarsal tubercle elliptical, about 1.5–2 times the size of outer, rounded metatarsal tubercle; supernumerary plantar tubercles small, round, low, and fleshy ( Fig. 1 );

13. coloration in ethanol, dorsum pale brown to grey with darker chevrons outlined by thin, white lines; cream to pink dorsolateral stripes; flanks with diagonal dark stripes, outlined by a thin, white line; venter pale brown with small, darker brown spots. Coloration in life, dorsum light brown to pale greyish green, with dark brown chevrons outlined by cream or white, and green blotches; dorsolateral folds orange; venter greyish brown to brown with darker, diffuse spots, and few small white spots; iris cream to golden with thin black reticulation and reddish brown horizontal streak; in females, groin and hidden surfaces of legs red ( Fig. 3 );

14. relatively small, SVL in females 20.9–23.2 mm (mean = 21.5 ± 1.14, N = 4), in males 17.2–17.4 mm (N = 2).

Similar species

In the Pacific slopes of the Andes, the only species that has a similar size, morphology, and colour pattern is P. verecundus ( Lynch & Burrowes, 1990) . Pristimantis verecundus is easily distinguished by having short dorsolateral folds that only reach the level of sacrum (dorsolateral folds extend posteriorly beyond the level of sacrum in P. mutabilis ). Females also have a unique chevron pattern on the throat ( Fig. 1 ), which is absent in P. mutabilis . Additionally, adult males of P. verecundus are slightly larger [18.0– 21.9 mm (N = 4); Lynch & Burrowes 1990] than males of P. mutabilis (17.2– 17.3 mm; N = 2), although sample sizes are low. Genetically, populations of P. verecundus and P. mutabilis are reciprocally monophyletic with strong support and have a substantial uncorrected genetic distance of 16.2– 16.8% in the combined 12S and 16S dataset ( Fig. 4 ; see Genetics below).

Pristimantis sobetes ( Lynch, 1980) co-occurs with P. mutabilis and also shares some morphological traits that could lead to misidentification (i.e. dorsolateral folds, dorsal colour pattern, skin texture plasticity). Pristimantis sobetes differs mainly by its non-overlapping larger size (adult male SVL = 20–23 mm; adult female SVL = 30–41 mm; Arteaga, Bustamante & Guayasamin, 2013), bright copper-red iris lacking a horizontal stripe (cream to gold iris with reddish horizontal stripe in P. mutabilis ), and by lacking red flash coloration on the groin and hidden surfaces of thighs (present in P. mutabilis females). Furthermore, P. sobetes is genetically distant from P. mutabilis and is placed in the P. surdus species group based on morphology ( Hedges et al., 2008); such placement is confirmed by genetics ( Fig. 4 ).

Description of the holotype

We provide a description based on the preserved holotype; however, we emphasize that skin texture variation is conspicuous (see Variation of skin texture section). Adult male (MZUTI 2190; Fig. 1 ). Head slightly longer than wide, narrower than body; upper eyelid bearing one conical tubercle and several low tubercles; head width 36.0% of SVL; head length 37.2% of SVL; snout of moderate length (snout to eye distance 16% of SVL), rounded in dorsal and lateral views; tongue longer than wide, with posterior margin round (not notched); eye diameter larger than eye–nostril distance; nostrils not protuberant, directed anterolaterally; canthus rostralis weakly concave in profile; loreal region slightly concave; upper eyelid width 94% of interorbital distance; cranial crests absent; tympanic annulus distinct, except for upper border, which is obscured by supratympanic fold; tympanic membrane distinct; two postrictal tubercles situated postero-ventrally to tympanic annulus; choanae elliptical, not concealed by palatal shelf of maxillary; vomerine odontophores postero-medial to choanae, low, oblique in outline, separated medially by distance less than width of odontophore, each bearing two teeth; skin on dorsum finely shagreen with interspersed low tubercles; low dorsolateral folds present; skin of throat and venter with numerous low, round warts homogenously distributed; no discoidal or thoracic folds; cloacal sheath absent; two low ulnar tubercles evident; outer palmar tubercle large, bifurcated distally ( Fig. 2 ); subarticular tubercles prominent, round; supernumerary palmar tubercles present, but few and low; fingers bearing narrow lateral fringes; Finger I conspicuously shorter than Finger II (Finger I length 70.6% of Finger II length); disc of Finger I slightly expanded; all other discs conspicuously expanded, elliptical in shape ( Fig. 3 ); ventral pads defined by circumferential grooves.

Tibia length 47.7% of SVL; foot length 48.3% of SVL; heel tubercle conical; tarsal tubercles small, barely evident; inner metatarsal tubercle oval, about twice the size of the outer, rounded tubercle; sub-articular tubercles round; plantar supernumerary tubercles indistinct; toes bearing narrow lateral fringes; webbing absent; all other toe discs expanded, rounded to elliptical in shape; toes with ventral pads well defined by circumferential grooves; relative length of toes: I <II <III <V <IV; Toe V longer than Toe III.

Measurements of type series and referred specimens: Meristic data are shown in Table 1.

Coloration in preservative

Dorsum pale brown to grey with darker chevrons outlined by thin, white lines; cream to pink dorsolateral stripes; arms, legs, and flanks with diagonal dark stripes, outlined by thin, white line; venter pale brown with small, darker brown spots, and minute white spots ( Fig. 1 ); iris silver.

Coloration in life

Dorsum light brown to pale greyish green, with bright green marks and grey to dark brown chevrons, outlined by thin cream or white line; dorsolateral folds orange; venter pale grey to brown with darker, diffuse spots, and few minute white spots; iris cream to golden with thin black reticulation and reddish horizontal streak; in females, groin and hidden surfaces of legs red ( Figs 2 , 3 ).

Variation of skin texture ( Figs 2 , 3 )

All individuals of Pristimantis mutabilis presented a markedly tubercular skin texture when found on vegetation or hidden in moss during the night. Large tubercles were evident on the dorsum, upper and lower lips, upper eyelid, arms and legs. After frogs were captured, they all showed a sudden and drastic change in skin texture; all tubercles became reduced in size, and the dorsal skin became smooth or nearly smooth (i.e., few tubercles are visible, mainly on the upper eyelid and heel). When frogs were returned to mossy, wet environments, they recovered a tuberculate skin texture. We speculate that explanatory variables involved in frog skin texture change are stress, humidity, and background. Our observations do not support light availability as a source of texture variation as we observed skin texture change at day and night. The time rate of skin texture variation might depend on the variables mentioned above; we only have one quantitative measure, which is summarized in Figure 2 .

Genetics

The genetic results supported the morphological analyses by placing the new species in the Pristimantis myersi species group ( Fig. 4 ), although the group itself is only strongly supported in Bayesian analyses and contains species from the P. unistrigatus group. Reciprocal monophyly of the new species is supported in maximum likelihood and Bayesian analyses (for 12S, 16S, and concatenated datasets) with high bootstrap and posterior probabilities ( Fig. 4 ). The populations from Reserva Las Gralarias and Reserva Los Cedros differ by large genetic distances of 5.0–6.5% while individuals from the same area show differentiation of 0.01– 0.04%. This result suggests the existence of a cryptic species, however data were not available to assess this possibility. We find substantial genetic differentiation between the new species and P. verecundus , which are morphological similar and possibly evolutionary sister species. We find genetic distances of 15.1–16.3% and 16.4–18.6% for the new species compared with P. verecundus for 12S and 16S, respectively. For the concatenated dataset, we find genetic distances of 16.2– 16.8% from P. verecundus .

Vocalization ( Fig. 5 , Table 2)

MZUTI 2190; adult male recorded from Reserva Las Gralarias on February 1, 2013; night with light rain, temperature of 14.2 °C. Pristimantis mutabilis emitted calls at an approximate rate of five calls per minute (N = 1). Three distinct types of calls were emitted by this species: (1) a single-note call with a single strong Time (ms) amplitude peak ( Fig. 5A ); (2) a single-note call with four or more strong amplitude peaks ( Fig. 5B ); and (3) a series of 5–6 calls with very short time intervals and frequency modulation increasing for each call throughout the series ( Fig. 5C ). The biological function of each call type is not known.

The first call type is composed of a single pulsed note that sounds like a short ring to the ear (N = 14; Fig. 5A ). The call has one strongly amplitude modulated pulse, and 2–4 weakly amplitude modulated pulses. The pulse rate of a call is 0.041 –0.111 pulses ms−1 (0.094 ± 0.019). The call duration is 45.7–49.0 ms (45.7 ± 1.3). Calls of this type are not frequency modulated and the dominant frequency of a call is 3273–3359 Hz (3285 ± 31). The lower limit of the fundamental frequency is 3255– 3346 Hz (3275 ± 39) and the upper limit is 3617– 3708 Hz (3688 ± 39).

The second call type is composed of a single pulsed note that sounds like a rough screech to the ear (N = 7; Fig. 5B ). The call has two or more strongly amplitude modulated pulses, and several weakly amplitude modulated pulses. The pulse rate of a call is 0.138 –0.274 pulses ms−1 (0.211 ± 0.041). The call duration is 68.0–99.0 ms (82.6 ± 11.0). Calls of this type are not frequency modulated and the dominant frequency of a call is 3358–3445 Hz (3421 ± 42). The lower limit of the fundamental frequency is 3256–3345 Hz (3269 ± 34) and the upper limit is 3708–3799 Hz (3773 ± 44). Notable non-overlapping differences of this call type from the first includes more than one strongly amplitude modulated pulse, a higher pulse rate, a longer duration, and a higher fundamental frequency.

The third call type is arranged in a series of 5–6 (5.6 ± 0.548) pulsed calls that sound like a long, coarse trill to the ear (N = 5; Fig. 5C ). The series duration is 301.0–456.0 ms (375.0 ± 56.0) with a series interval of 4.2– 7.3 s (5.3 ± 1.2). Each call has one strongly amplitude modulated pulse, and several weakly amplitude modulated pulses. The pulse rate is 0.055 – 0.089 (0.066 ± 0.010) and is most similar to call type A. The dominant frequency of a call is 3187–3445 Hz (3342 ± 94). Calls of this type have some frequency modulation increasing 86–173 Hz (141.7 ± 48.3) throughout the series. The lower limit of the fundamental frequency is 3165–3346 Hz (3256 ± 64) and the upper limit is 3708–3799 Hz (3744 ± 50). Notable nonoverlapping differences of this call type from the first and second type are that calls are arranged in a series and frequency modulated.

Etymology

The specific epithet mutabilis is the Latin word for changeable and refers to the ability of this species to modify its skin texture.

Distribution ( Fig. 6 )

Pristimantis mutabilis is known from the following Andean localities in northwestern Ecuador: Reserva Las Gralarias (0.0167° S, 78.7333° W, 2063 m, Pichincha province) and Reserva Los Cedros (Sendero Oso: 0.3197° N, 78.7858° W, 1880 m; Sendero Cascada Nueva: 0.3249° N, 78.7809° W, 1850 m, Imbabura province) .

Natural history

Pristimantis mutabilis has been found in both primary and secondary Andean forests. At Reserva Las Gralarias, the two males (MZUTI 2190, 2191) were found con- cealed in moss on a tree 230 cm above the ground; calling males were heard during January and February 2013. Additionally, other individuals (MZUTI 413; 909–913) were found on the surfaces of leaves about a metre above the ground ( Fig. 3A ). All individuals were observed to be displaying the tuberculate state while perched on leaves.

At the two localities where Pristimantis mutabilis has been recorded, the species seems to be abundant, based on the vocalizations that are commonly heard during the night. However, given the arboreal habits of the species, observations are rare. As an example, at Reserva Las Gralarias, we have only observed three individuals during a three-year study.

Conservation status

Given the available information on Pristimantis mutabilis , and following IUCN (International Union for Conservation of Nature) (2001) criteria, we suggest placing this species in the Data Deficient category.

Figures

Figure 1. (A, B, Pristimantis mutabilis sp. nov., holotype, MZUTI 2190, in preservative. C, D, Pristimantis verecundus, holotype, IND-AN 1834, in preservative.

Figure 2. Skin texture variation in one individual frog (Pristimantis mutabilis) from Reserva Las Gralarias (Pichincha, Ecuador). Note that skin texture shifts from highly tubercular to almost smooth; also, note the relative size of tubercles on the eyelid, lower lip, and limbs. The frog was found on a leaf during the night (left photograph) and photographed in the laboratory (photograph with white background) the following morning.

Figure 3. Pristimantis mutabilis sp. nov. in life. A, B, Sub-adult male, MZUTI 2191, photographed in its natural habitat during the night (top left) and under laboratory conditions during the day (top right). C, Adult female in dorsolateral view, MZUTI 910. D, Adult female in ventral view, MZUTI 911.

Figure 4. Maximum likelihood (ML) and Bayesian (BA) genetic topology for the combined 12S and 16S dataset. Separate gene trees not shown because the results were similar. The circles at the nodes show ML and BA significant support values (ML: bootstrap> 75%; BA: posterior probability> 0.95). The lack of a circle indicates that the node was not significantly supported by either analysis. The (1) and (2) represent two possible evolutionary scenarios given current data. Scenario 1 hypothesizes that skin texture plasticity originated independently twice while Scenario 2 hypothesizes that skin plasticity originated once in the common ancestor to the P. myersi and P. surdus groups.

Figure 5. Oscillogram and spectrogram for the three call types A–C, of Pristimantis mutabilis on the same time scale. Note that call type C is a series of calls.

Figure 6. Map showing the distribution of Pristimantis mutabilis (white circles) in Ecuador.