English: Alfaro’s treefrog; Spanish: Rana arbórea de Alfaro

QCAZ 43262 (field no. SC-PUCE 23245), adult male from Ecuador, Provincia Orellana, Parque Nacional Yasuní, 1 km from Northern Production Facilities (NPF) oil camp (0.6893°S, 76.4290°W), 238 m above sea level, collected by Marcel A. Caminer and Edwin Carrillo Ponce on 20 June 2009.

QCAZ 43260–61, 43263, adult males, collected with the holotype.

ECUADOR: PROVINCIA ORELLANA: Río Napo, Nuevo Rocafuerte, (0.9192°S, 75.4010°W), 187 m, QCAZ 44788–89, 44790–91, adult males, collected by S. R. Ron, E. Toral and I. G. Tapia on 10 July 2009; Nuevo Rocafuerte, Alta Florencia (0.8966°S, 75.4370°W), 187 m, QCAZ 39510, adult male, collected by S. D. Padilla and P. Vargas Mina on 29 October 2008; Río Napo, Huiririma (0.7116°S, 75.6239°W), 194 m, QCAZ 44634–35, adult males, collected by S. R. Ron, E. Toral and I. G. Tapia on 8 July 2009; Río Napo, San Vicente (0.6790°S, 75.6511°W), 203 m, QCAZ 44527, adult male, 44528, adult female, collected by S. R. Ron, E. Toral and I. G. Tapia on 7 July 2009; Río Napo, Chiroisla (0.5756°S, 75.8998°W), 203 m, QCAZ 44351, adult female, 44425, adult male, collected by S. R. Ron, E. Toral and I. G. Tapia on 5 July 2009; Río Napo, Edén (0.4983°S, 76.0711°W), 216 m, QCAZ 39631, 44180, adult females, 44191, adult male, collected by S. Aldas, S. R. Ron, E. Toral and I. G. Tapia on 21 January 2009 and 4 July 2009; Río Napo, Añangu (0.5249°S, 76.3844°W), 255 m, QCAZ 43977–78, adult males, collected by S. R. Ron, E. Toral and I. G. Tapia on 1 July 2009; Estación Científica Yasuní, Universidad Católica del Ecuador (0.6748°S, 76.3844°W), 231 m, QCAZ 43249–50, 43253, 43255 adult males, 43251–52, 43254, adult females, same collectors as the holotype between 18–19 June 2009; Estación Científica Yasuní, Universidad Católica del Ecuador (0.6748°S, 76.3844°W), 219 m, QCAZ 19328, adult female, collected by I. G. Tapia and G. Carotti on 20 February 2002; Río Napo, sector La Primavera (0.4442°S, 76.7868°W), 244 m, QCAZ 43826, adult male, collected by S. R. Ron, E. Toral and I. G. Tapia on 29 June 2009; Río Napo, sector La Primavera, El Descanso (0.4310°S, 76.7864°W), 244 m, QCAZ 43894, adult female, collected by S. R. Ron, E. Toral and I. G. Tapia on 30 June 2009; El Coca (0.4778°S, 76.9898°W), 267 m, QCAZ 559, adult male, collected by Giovanni Onore on 1 April 1984, QCAZ 43682, adult male, 43683–84, adult males, collected by S. R. Ron, E. Toral and I. G. Tapia and 27 June 2009; PROVINCIA SUCUMBÍOS: Playas del Cuyabeno (0.2654°S, 75.8917°W), 230 m, QCAZ 28272, 28398, adult females, 28278, adult male, collected by M. R. Bustamante, N. Acosta-Buenaño, M. Guerra and C. Proaño between 7–8 October 2003; Puerto Bolívar (0.0886°S, 76.1420°W), 240 m, QCAZ 28240, adult male, collected by P. Menéndez and M. R. Bustamante on 5 August 2003; Río Napo, La Selva Lodge (0.5086°S, 76.3649°W), 229 m, QCAZ 44025, 44027, adult males, collected by S. R. Ron, E. Toral and I. G. Tapia on 2 July 2009; Río Napo, 2.5 km S from Pañacocha (0.4712°S, 76.6667°W), 225 m, QCAZ 44851, 44853, 44858, adult males, 44856, adult female, collected by S. R. Ron, E. Toral and I. G. Tapia on 3 July 2009; 2.5 km N from Nueva Loja (0.0917°N, 76.8901°W), 350 m, QCAZ 33983, adult female, 33984, adult male, collected by S. Valdivieso, D. Tirira, J. Wiens and L. A. Coloma on 17 March 1990; Pañacocha, Moretal Sur (0.2758°S, 75.9352°W), 212 m, QCAZ 50785, juvenile, collected by R. Betancourt on 11 February 2011.

ECUADOR: PROVINCIA ORELLANA: Río Napo, Nuevo Rocafuerte, (0.9192°S, 75.4010°W), 187 m (QCAZ 44789); Río Napo, Huiririma (0.7116°S, 75.6239°W), 194 m (QCAZ 44632–33); Río Napo, San Vicente (0.6790°S, 75.6511°W), 203 m (QCAZ 44525–26); Río Napo, Chiroisla (0.5756°S, 75.8998°W), 203 m, (QCAZ 44424, 44426–27, 44429); Río Napo, Edén (0.4983°S, 76.0711°W), 216 m, (QCAZ 44181, 44249); Estación Científica Yasuní, Universidad Católica del Ecuador (0.6702°S, 76.4376°W), 231 m (QCAZ 8466, 8469, 11883, 19203, 49153); Río Napo, sector La Primavera, El Descanso (0.4310°S, 76.7864°W), 244 m (QCAZ 43895–96); Parque Nacional Yasuní, Pozo SPF, 250 m (QCAZ 31257–59); Nuevo Rocafuerte, Tambococha (0.9783°S, 75.4256°W), 177 m (QCAZ 55226, 55232, 55296, 55363, 55432–33); PROVINCIA SUCUMBÍOS: Playas de Cuyabeno (0.2654°S, 75.8917°W), 230 m (QCAZ 28383–84, 28391, 28397); Puerto Bolívar (0.0886°S, 76.1420°W), 240 m (QCAZ 27815, 28190, 28211, 28230, 28232, 28310, 28315); Río Napo, entrance to La Selva Lodge (0.5086°S, 76.3649°W), 229 m (QCAZ 44022–24, 44026, 44028); La Selva Lodge, Limoncocha (0.4981°S, 76.3738°W), 245 m (QCAZ 25401, 25408, 25410, 25417); Río Napo, 2.5 km S from Pañacocha (0.4712°S, 76.6667°W), 225 m (QCAZ 44848–50, 44852, 44854–55, 44857); 2.5 km N from Nueva Loja (0.0917°N, 76.8901°W), 350 m (QCAZ 2797).

Hypsiboas alfaroi (Fig. 4E, 8E and 18) is characterized by: (1) mean SVL 32.80 mm in males (range 27.91–36.27; n = 32), 44.51 mm in females (range 39.68–49.21; n = 12); (2) basal webbing on fingers; (3) tubercle on heel; (4) dorsal coloration varying from creamy white to grayish brown or brown, sometimes with dark markings (e.g., broad transversal bands, narrow longitudinal lines); (5) faint brown middorsal line often present; (6) flanks creamy white or gray (in life, blue in large females and light blue or white in males) with dark brown dots or blotches; (7) hidden surfaces of thighs creamy white, gray or brown (in life, blue in large females and light blue or white in males) with dark brown dots or blotches; (8) ventral surfaces of thighs creamy white, yellowish white or brown; (9) ventral areas creamy white or yellowish white with brown flecks on the head, neck, and chest; (10) webbing on feet; (11) in life, iris yellowish, bronze or cream with faint yellow coloration on its upper margin; (12) prepollical spine present in males.

Hypsiboas alfaroi is most similar to Hypsiboas tetete sp. n. but it can be distinguished by having a markedly different advertisement call (Fig. 13C–H). Although with overlapping values, Hypsiboas alfaroi has a smaller tympanum (relative to SVL, mean male TD/SVL = 0.06, SD = 0.01, n = 32; Hypsiboas tetete sp. n. mean male TD/SVL = 0.08, SD = 0.009, n = 5; differences are significant: t = –3.21, df = 35, P = 0.003). Hypsiboas alfaroi differs from Hypsiboas fasciatus, Hypsiboas almendarizae, Hypsiboas calcaratus, and Hypsiboas maculateralis in advertisement call (Figs 12A–F and 13A–D) and by having a small tubercle on the heel instead of a large calcar. Hypsiboas alfaroi further differs from Hypsiboas fasciatus, Hypsiboas almendarizae, and Hypsiboas calcaratus by having dark brown dots on the flanks (vertical dark lines in Hypsiboas fasciatus, Hypsiboas almendarizae, and Hypsiboas calcaratus). Morphological characters useful to differentiate Hypsiboas alfaroi from other species are shown in Table 6.

Adult male, 32.06 mm SVL, foot length 13.22 mm, head length 8.77 mm, head width 10.02 mm, eye diameter 3.69 mm, tympanum diameter 2.19 mm, tibia length 18.74 mm, femur length 16.24 mm, arm length 5.71 mm, eye-nostril distance 2.59 mm, head wider than long and wider than body; snout rounded in lateral view, truncate in dorsal view; distance from nostril to eye shorter than diameter of eye; canthus rostralis indistinct, rounded; loreal region concave; internarial area convex; nostrils not protuberant, directed laterally; interorbital area slightly convex; eye large, strongly protuberant; diameter of eye 1.7 times diameter of tympanic annulus; tympanum concealed beneath skin;tympanic annulus evident, ovoid, longer dorsoventrally and concealed dorsally by supratympanic fold, separated from eye by ca. 1.01 times its diameter; posterior end of supratympanic fold reaches anterior border of arm insertion. Arm slender, axillary membrane absent; indistinct low tubercles present along ventrolateral edge of forearm; relative length of fingers I<II<IV<III; fingers bearing large, oval discs, that of third finger about three fourths of tympanum diameter; subarticular tubercles prominent, round to ovoid, single; supernumerary tubercles present; palmar tubercle small, elongated; prepollical tubercle large, flat, elliptical; prepollex enlarged, claw shaped; nuptial excrescences absent; webbing absent between fingers. Small tubercle on tibiotarsal articulation; ill defined, scattered tubercles on tarsus and along ventrolateral edge of foot; toes bearing discs slightly wider than long, smaller than those of fingers; relative length of toes I<II<V<III<IV; outer metatarsal tubercle ill defined, small, round; inner metatarsal tubercle large, elongated, elliptical; subarticular tubercles single, round, flat; supernumerary tubercles restricted to the soles; webbing formula of toes I2—2II2—3III2—3IV3—1¾V. Skin on dorsum, head, and dorsal surfaces of limbs smooth; skin on flanks smooth with weak longitudinal wrinkles posterior to the arm; skin on venter coarsely granular; skin on ventral surfaces of head and thighs granular, those of shanks smooth. Cloacal opening directed posteriorly at upper level of thighs; short simple cloacal sheath covering cloacal opening; round tubercles below and on the sides of vent. Tongue ovoid, widely attached to mouth floor; vomerine odontophores triangular, narrowly separated, posteromedial to choanae, bearing 10 vomerine teeth on each side; choanae trapezoidal, oblique.

Color of holotype in preservative. Dorsum grayish brown with five to six broad diffuse brown transversal bands; scattered minute black dots on dorsal surfaces; few small cream dots restricted to the posterior dorsum; faint brown narrow middorsal line restricted to the head; flanks creamy white with dark brown dots; dorsal surfaces of hindlimbs and forelimbs grayish brown with narrow transversal brown bars (one or two on each upper arm and forearm, and three or four on each thigh, shank, and tarsus); hidden surfaces of thighs grayish brown with dark brown dots; venter creamy white with brown flecks on head, neck, and chest; ventral surfaces of hindlimbs and forelimbs yellowish white with a narrow to wide brown stripe on the outer edge of the hands, forearms, tarsal folds, and feet; bones white.

The specific name is a noun in the genitive case and is a patronym for Eloy Alfaro Delgado, former Ecuadorian president (1897–1901 and 1906–1911) and leader of the liberal revolution in Ecuador. His government promoted the separation between church and state and the modernization of Ecuador by supporting education and large-scale systems of transportation and communication.

Variation in dorsal and ventral coloration of preserved specimens is shown in Figure 18. Background dorsal coloration varies from creamy white (e.g., QCAZ 44429) to pale grayish brown (e.g., QCAZ 19328), grayish brown (e.g., QCAZ 44180), pale brown (e.g., QCAZ 28398) or brown (e.g., QCAZ 28272). Irregular dorsal marks may be present in diverse patterns. A faint dark middorsal line extends from the tip of the snout to the mid-dorsum (e.g., QCAZ 43895) or the sacral region (QCAZ 44025), but in some specimens it is restricted to the head (e.g., QCAZ 55926) or is altogether absent (e.g., QCAZ 28272). There is variation in the number, size, and shape of the dorsal marks. Five to seven diffuse broad transversal bands on the dorsum (sometimes interconnected), and narrower brown transversal bars on the dorsal surfaces of the limbs (one or two each on the arm and forearm, and three to five each on the thigh, shank, and foot) may be present (e.g., QCAZ 28272). Faint, narrow longitudinal lines may be present on the dorsum (e.g., QCAZ 44858, 43263). The dorsum and dorsal surfaces of limbs can have scattered black or white dots (e.g., QCAZ 43263, 28398). The coloration of flanks varies from creamy white to gray with irregular dark brown spots distributed from the groin to the mid-flank. In some individuals, similar spots can also be present in the hidden surfaces of the thighs, shanks, ventral surfaces of the forelimbs, and dorsal surfaces of the feet (e.g., QCAZ 28272). The hidden surfaces of thighs sometimes have dark brown blotches (QCAZ 28272).

Ventral areas of preserved specimens vary from creamy white (e.g., QCAZ 28398, 44180) to yellowish white (e.g., QCAZ 43263) with dark flecks on the head, neck, and chest (Fig. 18). In some individuals, the flecks are also present on hindlimbs, forelimbs, and belly (e.g., QCAZ 28272, 28398). A narrow to wide brown stripe is present in some individuals on the outer edge of the hands, forearms, thighs, tarsal folds, and feet (e.g., QCAZ 43263). Coloration of webbing and disc vary from brown to gray. Vomerine odontophores are triangular (with arched base in some specimens). Bones are white.

In the adult type series, the largest male has a SVL of 36.27 mm, and the largest female 49.21 mm; mean male SVL = 32.80 mm (n = 32; SD = 1.97), mean female SVL = 44.51 mm (n = 12; SD = 3.09). Females were significantly larger than males (t = -14.94, df = 42, P < 0.001). Inter-population variation in size and other morphometric variables are shown in Tables 1 and 2.

(based on photographs; Figs 4E and 8E). Dorsal surfaces vary from pale creamy white (e.g., QCAZ 39631) to yellowish tan (e.g., QCAZ 43261), reddish brown (e.g., QCAZ 43254) or brown (e.g., QCAZ 43978) with a faint brown middorsal line (e.g., QCAZ 43978); sometimes, broad pale brown transversal bands are present on the dorsum (e.g., QCAZ 43978); narrow pale brown transversal bars (e.g., QCAZ 43683) or narrow pale brown longitudinal lines (e.g., QCAZ 44635) may ornament the dorsal surfaces of the limbs; scattered minute black dots on the dorsum may be present (e.g., QCAZ 44635); flanks are white, light blue or blue with irregular dark brown spots (e.g., QCAZ 43683) or blotches (e.g., QCAZ 43252); hidden surfaces of thighs are gray, white, light blue or blue with dark brown irregular spots (e.g., QCAZ 43683) or blotches (e.g., QCAZ 39631); in some specimens, the hidden surfaces of the shanks and dorsal surfaces of the feet have similar brown spots (e.g., QCAZ 43254); venter creamy white (e.g., QCAZ 43254) or yellowish with creamy white belly (e.g., QCAZ 43260); conspicuous brown flecks are present on the ventral areas of the head, neck, and chest (e.g., QCAZ 44635); ventral surfaces of hindlimbs and forelimbs are translucent white (e.g., QCAZ 43683) or yellowish (e.g., QCAZ 43260); in some specimens, the ventral surfaces of the thighs are creamy white (e.g., QCAZ 43254); discs and webbing are brown (e.g., QCAZ 43978), yellowish (e.g., QCAZ 43261) or pale cream (e.g., QCAZ 39631); a narrow to wide brown stripe may be present on the outer edge of the hands, forearms, thighs, feet, and tarsal folds (e.g., QCAZ 43978); iris yellowish (e.g., QCAZ 43683), bronze (e.g., QCAZ 43254) or cream with a subtle yellow tone on its upper quarter (e.g., QCAZ 44635); coloration of bones varies from white (e.g., QCAZ 43252) to green (e.g., QCAZ 43683).

Three males were recorded at Estación Científica Yasuní PUCE (Provincia Orellana) on 20 June 2009. The call (Fig. 13C–D) consists of four to five trill-like notes with a mean duration of 0.20 s (SD = 0.05) and mean rise time of 0.07 s (SD = 0.03). Other call parameters are listed in Table 7.

Hypsiboas alfaroi occurs in the Ecuadorian northern Amazon region (Napo, Orellana, and Sucumbíos provinces; Fig. 15). Localities with known elevation range from 176 m (Nuevo Rocafuerte) to 350 m (Nueva Loja). Nuevo Rocafuerte is on the border between Ecuador and Peru; the occurrence of Hypsiboas alfaroi in Peru is highly likely.

Specimens from Nuevo Rocafuerte, Playas de Cuyabeno, Puerto Bolívar, Estación Científica Yasuní of Universidad Católica del Ecuador, and Nueva Loja were found at night in primary and secondary forest, perching on vegetation 50 to 180 cm above the ground, in flooded areas, swamps, near streams and in forest away from water bodies. Individuals at San Vicente were found in pastures, secondary forests, flooded grassland, and ponds.

Vegetation types for Ecuadorian localities are: (1) Amazonian Lowland Evergreen Forest, characterized by high plant alpha-diversity and a canopy of 30 m with emergent trees that reach 40 m, (2) Floodplain Lowland Forest of White Waters, characterized by periodical flooding with white waters from large rivers and vegetation that reaches 35 m of height with several vegetation strata, and (3) Lowland Forest of Palms and black-waters, swamps characterized by a canopy of 30 m with dense understory and a dominance of the palm Mauritia flexuosa.

The distribution polygon of Hypsiboas alfaroi has 47,524 km². Within it, 4,287 km² (9.0%) have been degraded by human activities, especially agriculture and cattle raising (estimated from Ministerio de Ambiente del Ecuador 2013). Because its distribution range is relatively large and has a low proportion of degraded habitat, we propose that Hypsiboas alfaroi be assigned to the Least Concern category.