Microkayla huayna, Riva & Cortez & Burrowes, 2017

Riva, Ignacio De La, Cortez, Claudia & Burrowes, Patricia A., 2017, A new species of Microkayla (Anura: Craugastoridae: Holoadeninae) from Department La Paz, Bolivia, Zootaxa 4363 (3) : -

Microkayla huayna sp. nov.

( Figs. 1–3 )

Microkayla sp. “Coscapa” (De la Riva et al., 2017).

Holotype. CBF 6630 (field tag CCF [Claudia Cortez Fernández] 167), adult male from Cañaviri (16º10’38.6” S, 68º08’19.2” W, 3465 m a.s.l), Valle de Zongo, Province Murillo, Departament La Paz, Bolivia, collected on 7 Jan. 2007 by Claudia Cortez.

Paratypes. Three specimens: MNCN 46991 (field tag 4412), adult male from Km 6.7 on the road from Valle de Zongo to Coscapa (16º07'09.8"S, 68º08'00.0"W, 3550 m a.s.l.), Province Murillo, Departament La Paz, Bolivia, collected on 4 Nov. 2012 by Ignacio De la Riva and Patricia A. Burrowes; CBF 1685, adult male, and CBF 1693, adult female, from Llaulluni (16º10'5.21" S / 68º07'45.34"W, 3417 m a.s.l.), Valle de Zongo, Province Murillo, Departament La Paz, Bolivia, collected on 14 September 1991 by Eduarno Forno.

Diagnosis. The new species is assigned to the genus Microkayla, as defined by De la Riva et al. (2017). Frogs of the allied genus Bryophryne Hedges, Duellman & Heinicke are morphologically similar to Microkayla, but these genera are not sister taxa, and Bryophryne does not occur in Bolivia, so far being known only from the Department of Cusco and adjacent areas of Puno, in southern Peru (De la Riva et al. 2017). Microkayla huayna sp. nov. is characterized by the following combination of characters: (1) Medium size (maximum Snout–Vent Length [SVL] 26.6 mm), body moderately robust, legs moderately short (Tibia Length [TL] + Foot Length [FL] = 75.6% SVL); (2) tympanic membrane and tympanic annulus present, poorly visible; (3) first finger slightly shorter than second; (4) tips of digits slightly swollen, not expanded laterally, lacking circumferential grooves and, in males, nuptial excrescences; (5) webbing of toes and lateral fringes absent; (6) two metatarsal tubercles, tarsal fold absent; (7) dorsal skin and flanks shagreen with scattered small warts; ventral skin finely granular; (8) snout rounded in dorsal view and in profile; (9) dorsum uniformly reddish brown or with small yellowish blotches; (10) venter fleshy cream, chest and throat dark brown.

Among the eight species of Microkayla so far described from the Cordillera Real, the new species is superficially similar to M. wettsteini (Parker, 1932) and M. condoriri (De la Riva, Aguayo & Padial, 2007), which furthermore are, together with M. chacaltaya (De la Riva, Padial & Cortez, 2007) and M. teqta (De la Riva & Burrowes, 2014), the species whose localities are geographically closer to that of M. huayna . From M. wettsteini the new species differs mostly by its smaller size (maximum male SVL 26.6 mm [range = 20.9–26.6; N = 3] vs. 31.0 mm in males of M. wettsteini [ Ergueta 1993]), and shorter hindlimbs (TL + FL = 75.6% SVL vs. 80% in M. wettsteini [De la Riva 2007]). From M. condoriri, the new species can be distinguished by having dorsal skin shagreen (smooth in M. condoriri) and longer hindlimbs (TL + FL = 75.6% SVL, vs. 70% in M. condoriri [De la Riva 2007]). The new species is distinguished from M. teqta by males being larger (maximum male SVL 26.6 mm vs. 23.6 mm in males of M. teqta), having a large subgular vocal sac (less developed in M. teqta), and lacking yellow or red blotches on dorsum or venter; additionally, the call of the new species is tonal, while that of M. teqta is pulsed (De la Riva & Burrowes 2014). Microkayla huayna sp. n. is distinguished from M. chacaltaya by being much larger (maximum SVL 26.6 mm vs. 20.4 mm in M. chacaltaya), having longer hindlimbs (TL + FL = 75.6% SVL vs. 70% in M. chacaltaya), and males possesing a large vocal sac (poorly developed in M. chacaltaya). Other congeneric species occurring in more distant parts of the Cordillera Real are M. ankohuma (Padial & De la Riva, 2007), M. iani (De la Riva, Reichle & Cortez, 2007), M. illampu (De la Riva, Reichle & Padial, 2007), and M. illimani (De la Riva & Padial, 2007). Microkayla huayna sp. nov. differs from M. ankohuma by having a brown dorsum (greenish-gray in M. ankohuma) and venter fleshy cream (black with large, irregular pale gray blotches); from M. iani by being much larger (maximum male SVL 26.6 mm vs. 19.9 mm in M. iani); from M. illampu by having dorsal skin shagreen (granular in M. illampu), dorsum brown, and venter fleshy cream (dorsum and venter black); and from M. illimani by being larger (maximum male SVL 26.6 mm vs. 22.3 mm in M. illimani) and lacking orange blotches on venter and groins.

Description of the holotype ( Figs. 1–3 ). Body moderately robust; dorsal skin shagreen with scattered small warts, more abundant on posterior part of body; in life, two rows of warts forming an irregular X-shaped pair of folds on the central part of dorsum (not visible in preservative due to changes in skin texture; Fig. 2 ); ventral skin finely granular; no thoracic fold; head wider than long, its width 37.2% of SVL; head length 30.4% of SVL; snout moderately long, slightly rounded in dorsal view, rounded and gently sloping in profile ( Fig. 3 ); nostrils not protuberant, directed laterally, closer to snout than to eyes; canthus rostralis poorly marked, straight in dorsal view and slightly convex in profile; eye-nostril distance 88.5% of eye length; loreal region barely concave, interorbital region flat, lacking cranial crests; tubercles on upper eyelid absent; tympanic membrane and tympanic annulus present, barely visible; supratympanic fold short, weak; postrictal tubercles absent; tongue large, oval; choanae oval, small, widely spaced; dentigerous processes of vomers absent; vocal slits present. A large subgular vocal sac. Limbs moderately short; tips of digits slightly swollen, not expanded laterally, lacking circumferential grooves; ulnar tubercle and fold absent; inner palmar tubercle single, oval, smaller than round outer, almost in contact to each other; fingers not fringed; subarticular tubercles round, well defined; supernumerary tubercles, round, small; first finger slightly shorter than second, relative length of fingers 1<2<4<3 ( Fig. 3 ); tibia length 36.5% of SVL; tarsus lacking tubercle and fold; two round, approximately equally-sized metatarsal tubercles; a few round, small supernumerary tubercles; subarticular tubercles round, slightly swollen; toes long, slender, not webbed, lateral fringes absent; relative length of toes 1<2<3=5<4 ( Fig. 3 ); foot length 39.1% of SVL.

Measurements (in mm) of the holotype. Snout–vent length, 26.6; head length (from rictus to tip of snout), 8.1; head width (at level of rictus), 9.9; internarial distance, 2.6; eye–nostril distance, 2.3; eye diameter, 2.6; tibia length, 9.7; foot length (from proximal border of inner metatarsal tubercle to tip of fourth toe), 10.4 (see Table 1).

Coloration. In preservative, the dorsum, head, and dorsal parts of the extremities are pale brown with irregular darker areas, especially on eyelids and upper flanks from behind the eyes to the middle of the body ( Fig. 2 ). There are some cream, small, irregular markings on the tympanic region and the upper lips, and a fine, cream middorsal stripe starting on the scapular region and reaching the cloaca, where it surrounds it; a similar line is present on the proximal part of the posterior surface of the thighs. The venter and ventral surfaces of the limbs, as well as the palmar and plantar surfaces are pale cream ( Fig. 2 ). The throat and the chest are dark gray. In life ( Fig. 1A ), the dorsal surfaces were reddish brown with the head and flanks slightly darker; there were some yellowish-cream small blotches around the tympanum and between the postcommisural region and the forelimb; the vertebral line was pale brown-cream, the belly and ventral surfaces of limbs were fleshy cream, and the chest and throat dark grayish brown; the axillae and groins were translucent, and the palmar and plantar surfaces fleshy brown, with the tips of digits reddish. The iris was golden superiorly and bronze in the lower part, with fine cream flecks.

Variation. Paratype MNCN 46991 ( Fig. 1B–D ) is similar to the holotype in morphology, although its color pattern is more striking. In life it had two faint dorsolateral ridges from the posterior edge of the eye to the middle of the body, and an X-shaped ridge in the central part of the dorsum. The dorsum was brown with small yellowish blotches and a fine, pale vertebral line from the interocular region to the vent. The dorsal surfaces of the limbs were paler than the dorsum, while the head was darker; the lips and the tympanic region had minute greenish-beige blotches. There was a cream line on the anterior surface of the thighs. As the holotype, this specimen has a large, dark brown (almost black), gular sac, this color covering the chest, reaching beyond the thoracic fold; the anterior half of the venter was dark brown with diffuse bluish blotches, while the posterior part was fleshy-colored, with bluish-gray tones. There is a bluish-gray (cream in preservative) line along the lower surface of each forearm, both lines merging in the middle of the thoracic fold, from where another line departs along the midventer. The ventral surfaces of the limbs and the palmar and plantar surfaces were fleshy beige (cream in preservative). The iris was grayish green, with black reticulations. In preservative, male paratype CBF 1685 is uniformly brown above, with the gular region dark brown, and the venter cream with brown, diffuse reticulations, more marked on the chest and less on the belly. Finally, the female paratype CBF 1693 is brown above, with a pair of dark suprainguinal spots and, as in the holotype, there is a cream, fine vertebral line from the interocular region to the vent, then extending along the posterior surface of each thigh. Morphometric variation of the type series is given in Table 1.

Advertisement call. Recordings of the advertisement call were obtained from the holotype, right before collecting it. The distance from the individual to the microphone was less than a meter. At the time of recording (18.40 h) the air temperature and the relative humidity were, respectively, 14.9 ºC and 83%. The call of M. huayna ( Fig. 4 ) consists of a short, tonal, whistle-like note. A total of 19 calls were recorded in four call groups of 4–7 calls, with call groups separated by long intervals of 19–29 seconds. Calls were emitted at a rate of approximately 25 notes/minute within call groups. The mean call duration is 0.363 s (range = 0.328–0.381; SD = 0.01; N = 19), and the mean interval duration between calls within call groups is 2.046 s (range = 1.438–2.927; SD = 0.389; N = 15). Within calls, there is upwards frequency modulation, reaching a peak near the end, and then descending again. The mean dominant frequency at the peak is 1930.5 Hz (range = 1851.6–2015.6 Hz; SD = 57.51; N = 19), and the mean frequency increase from the beginning of the note to the peak is 101.16 Hz (range = 70.3–140.6 Hz; SD = 24.76; N = 19). There is a harmonic frequency with a mean peak at 3810.8 Hz (range = 3703.1–4007.8 Hz; SD = 248.18; N = 19), which has 20–30 dB less than the call.

Distribution and ecology. This species is known only from three localities at a similar altitude ( Fig. 5 ), in the upper limits of the cloud forests that cover the Zongo Valley at intermediate elevations ( Fig. 6 ). The two most distant localities (Cañaviri and road to Coscapa) are separated by an air distance of 6.1 km; Llaulluni is only 1.1 km from Cañaviri, down the valley from this locality. At Cañaviri, the holotype was amidst stones and vegetation by day, close to the river and around the houses of the village ( Fig. 6 ). At least ten males separated 3–5 m from one another were calling approximately every 15 minutes. The locality where the paratype MNCN 46991 was collected lies on a valley parallel to the Zongo Valley, on the road from Cañaviri to Coscapa. Here, several males were calling at 17:00 h, at an air temperature of 9ºC. The call of these males (not recorded) consisted of a single wistlelike note equal to that recorded at the type locality, but sometimes two or three shorter notes followed the main note. The paratype MNCN 46991 was found under a stone by day near a dry creek surrounded by rocks and bushes, in an area partially grazed by cattle. At the time of collecting the paratype, males of Pristimantis platydactylus (Boulenger, 1903) were calling both along the road to Coscapa and at the type locality, as well as in other localities nearby.

Etymology. The specific name refers to the Huayna Potosí peak (6088 m; Fig. 7 ), one of the most beautiful mountains of the Cordillera Real, on the left side of the upper valley of the Zongo river, near the type locality of the species. Huayna Potosí means “young mountain” in Aymara language.

Figures

FIGURE 1. Living specimens of Microkayla huayna sp. nov. A) Lateral view of holotype CBF 6630 (adult male, SVL 26.6 mm) from Cañaviri, Zongo Valley, La Paz, Bolivia. Dorsolateral view (B), lateral view (C), and ventral view (D) of paratype MNCN 46991 (adult male, SVL 26.6 mm) from the road Valle de Zongo-Coscapa, La Paz, Bolivia.

FIGURE 2. Dorsal and ventral views of the preserved holotype of Microkayla huayna sp. nov. (CBF 6630) (adult male, SVL 26.6 mm) from Cañaviri, Zongo Valley, La Paz, Bolivia.

FIGURE 3. Schematic drawings of the holotype of Microkayla huayna sp. nov. (CBF 6630) (adult male) from Cañaviri, Zongo Valley, La Paz, Bolivia. A) Plantar surface of left foot; B) palmar surface of left hand; C) head in lateral view. Scale bar = 10 mm.

FIGURE 5. Map of the central section of the Cordillera Real of Bolivia, showing the three known localities of Microkayla huayna sp. nov. and those of other species of the genus in the area.

FIGURE 6. Habitat of Microkayla huayna sp. nov. Left, the Zongo Valley (La Paz, Bolivia) showing its steep slopes covered with cloud forest; right, river Zongo at Cañaviri, the type locality of the new species.

FIGURE 7. Laguna Milluni, in the forefront, and peak Huayna Potosí (6088 m), as seen from the dry altiplano before the mountain pass to the Zongo Valley.

FIGURE4. Advertisement call of Microkayla huayna sp. nov. recorded from the male holotype (CBF 6630; SVL 26.6 mm)at the type locality (Cañaviri, Zongo Valley, La Paz, Bolivia; air temperature, 14.9 ºC; FFT resolution, 1024 points). A) Oscillogram of call series; B) spectrogram of call series; C) oscillogram of a single call; D) spectrogram of a single call.