Ololygon skuki, (Lima, Cruz & Azevedo) (Lima, Cruz & Azevedo, 2011)

Nascimento, Filipe A. C., Araujo-Vieira, Katyuscia, Dubeux, Marcos J. M., Marinho, Pedro, Guedes-Santos, Jhonatan, Roberto, Igor Joventino, Santos, Ednilza Maranhão Dos, Ávila, Robson Waldemar, Pombal Jr, José P. & Faivovich, Julián, 2024, Phylogenetic position, morphological data, call, and geographic distribution of the elusive treefrog Ololygon skuki (Hylidae: Hylinae: Scinaxini), Zootaxa 5493 (4), pp. 401-418 : 403-411

Results

Adult external morphology

The overall external morphology of the topotype specimens and type series of Ololygon skuki ( Fig. 1 ; Appendix 1), is congruent with the original description reported by Lima et al. (2011). However, we observed some characteristics that were either not informed in the description or differed from it, as follows (data from Lima et al. 2011 in parenthesis).

Vocal sac external, evident by loosened, partially expanded skin on the posterolateral portion of the gular region, single, subgular, ventrally not reaching the pectoral region (vocal sac single, median, subgular). Pectoral fold absent (not informed). Nuptial pad on Finger II light-colored, without distinct epidermal projections ( Fig. 2A, B ), extending from Metacarpal II to the base of the disc dorsomedially and ventrally obscuring almost entirely the inner metacarpal tubercle (nuptial pad undeveloped). Nuptial pad present on Finger III ( Fig. 2B ), covering the Metacarpal III dorsomedially or extending dorsomedially from Metacarpal III to the base of the disc, without distinct epidermal projections (not informed). Scattered acini (many or few) along the palm and on the ventrolateral region of fingers IV and V present in CFBH 47968 or absent in the remaining individuals (not informed). Glandular concentrations and spicule-shaped papillary epidermal projections absent on medial region of forearm, pectoral, gular (not informed), and inguinal regions (inguinal gland not developed). Some measurements are presented in Table 1 .

In addition to the characteristics mentioned above, we observed other minor variations among specimens of the type series MNRJ 70000, 70002–10, as follows: snout mucronate to slightly mucronate in dorsal view, with the snout point well marked with one tubercle or poorly marked with more than one tubercle; loreal region concave to almost oblique; tympanum rounded, well defined, except for the upper portion that is almost ovoid; supratympanic fold marked, but few developed, covering the upper portion of the tympanic ring (except in MNRJ 70002, 70009), with two or three (MNJR 70009) large tubercles (tubercles absent in MNRJ 70002–3, 70006, 70008); tubercles present or absent (MNRJ 70003–5, 70009–11) on flanks and dorsum of body, when present, more developed on the flanks; tubercles less developed, scattered on head; external border of forearms, tarsi, and feet with a row of tubercles (inconspicuous or absent in MNRJ 70002, 70006); belly granular, almost smooth in MNRJ 70001; darkcolored skin fold on wrist; outer metacarpal tubercle elliptical, ovoid or rounded; disc of Finger II and Toe I smaller than others; inner metatarsal tubercle nearly elliptical, ovoid, or rounded (MNRJ 70001); and outer metatarsal tubercle not visible.

Coloration. We observed some color variation in the individuals CFBH 47968 and MHNUFAL 12390, as follows:

In life, dorsum brown or black with a subtriangular, light brown or cream interocular blotch, anteriorly bordered by a dark brown or black line, and an irregular, light brown or cream blotch and a black transversal line on the sacral region; without evident longitudinal lines ( Fig. 3A–C ). Canthus rostralis and loreal region same coloration of dorsum, without lines or stripes ( Fig. 3E ). Dorsal surfaces of arms, forearms, hands, thighs, and feet with dark brown dots and small blotches (CFBH 47968; Fig. 3D ) or with dark brown bars (MHNUFAL 12390; Fig. 3B ) in a light brown background. Black line from posterior corner of eye to mid flank present (MHNUFAL 12390; Fig. 3B ) or absent (CFBH 47968; Fig. 3F ). In the specimen CFBH 47968 ( Fig. 3F ), axilla, inguinal region, and anterior surface of thighs with orange flash coloration; posterior surfaces of thighs spotted with orange and yellow on a black background; posterior surfaces of tibia with yellow dots and small blotches on a black background, poorly black transversal bars in the left tibia; ventrally, belly and throat light cream, with white granules; arms and forearms light cream; palms, soles, tibia, tarsi spotted with black; thigh finely spotted with black posteriorly. No information or photos of the hidden surfaces of thighs and tibia, inguinal region, and ventral view of the body in life were available for MHNUFAL 12390.

In preservative, the overall coloration pattern is similar to that in life, but diagonal bars (poorly defined) and transversal dark bars (on a white background) are visible on the dorsal and posterior surfaces of thighs in the individual CFBH 47968 ( Fig. 1 ). The orange and yellow have faded, becoming white.

Call

The call of Ololygon skuki (n = 3 calls; 93 notes analyzed; 1 unvouchered individual) is composed of a long series of pulsed notes, with a gradual rise in the sound intensity until the middle of the call train ( Fig. 4A ). The three calls last 3.7, 3.6, and 2.8 s, emitted at a rate of 0.36 calls/min, with intercall intervals of 3.6 and 4.6 min. Each call has 34, 33, and 26 notes, respectively. Notes last 0.03– 0.13 s (χ = 0.05 ± 0.01 s) and are emitted at a rate of 9.1– 9.4 notes/s (χ = 9.2 ± 0.2 notes/s), with internote intervals of 0.04– 0.13 s (χ = 0.06 ± 0.01 s). The first 10 or 11 notes are slightly shorter than the others. Each note consists of 25–42 well defined pulses (χ = 36.1 ± 3.8 pulses), which gradually increase in amplitude until the last third of the note and following gradually decrease ( Fig. 4B, C ). Pulses are emitted at a rate of 298–898 pulses/s (χ = 723 ± 85 pulses/s), with a sharp attack followed by a decreasing of sound intensity towards the beginning of the next pulse. Pulses tightly packed, and the amplitude modulation pattern is more distinctly visible on high amplitude notes. The fundamental frequency (minimum frequency) is 3,273.0– 4,392.7 Hz (χ = 4,079.7 ± 222.8 Hz) and the dominant frequency is 4,565.0–5,512.5 Hz (χ = 5,125.3 ± 222.4 Hz). Calls do not have harmonic structures, as their frequencies are not multiple of the fundamental frequency.

Phylogenetic analyses

The parsimony analyses resulted in 2,450 most parsimonious trees (mpts) of 87,703 steps. Given the goals of this study and the extensive size of the dataset from Araujo-Vieira et al. (2023), Figure 5 only shows the section of the phylogenetic results corresponding to the Ololygon argyreornata group. Our results showed that the O. argyreornata group is a well-supported clade (97% jackknife). Ololygon skuki was recovered as the sister taxon of all remaining species and related candidate species of the group ( Fig. 5 ). These include the four candidate species Ololygon spp. 2 , 4, 5, and 6, and two lineages of O. argyreornata A and B. Within this clade, Ololygon sp. 5 is the sister taxon (68% jackknife) of the pectinate series followed by Ololygon sp. 6 and a clade composed of the two lineages of O. argyreornata A and B and Ololygon sp. 4 and Ololygon sp. 2 (68% jackknife), where O. argyreornata A and B are poorly supported (68% jackknife) as sister taxa of Ololygon sp. 2 .

The individual from the municipality of São Sebastião do Passé , Bahia, Brazil, identified previously as Ololygon argyreornata (UFBA 10246; Dória et al. 2018: erroneously published as from the municipality of Catu , Bahia; pers. comm. Marcelo Napoli ), was recovered nested among specimens of O. skuki . This would be the first record of O. skuki in the state of Bahia, extending its known distribution approximately 425 km SW (straight line) from its type locality at Environmental Protection Area of Catolé and Fernão Velho, municipality of Maceió, Alagoas, Brazil ( Fig. 6 ). The UPDs (16S rDNA, ≈540 bp) between topotypic specimens and that from São Sebastião do Passé is 0.4%, while O. skuki differs in UPDs of 10.2 to 15.1% from Ololygon spp. 2 , 4, 5, and 6, and O. argyreornata A and B (see Table 2 ).

Natural history

Observations were carried out between 17:30 and 23:00 h at the type locality, in a temporary pond inside the forest, on different dates in April, May, and July 2011. The male was found calling in a horizontal position with heads upwards (approximately 2 m above ground), perched on a leaf of shrubs along the edges of the pond. No other calling individuals were heard nearby. The amplexus is axillary. Amplectant couples were observed on four different substrates: a trunk inside the pond, a fallen tree trunk at the pond’s edge, a leaf litter, and partially submerged in the pond water ( Fig. 7A–C ). At that time, adult males of Chiasmocleis alagoana Cruz, Caramaschi & Freire were occasionally found amplexing adult females of Ololygon skuki ( Fig. 7D ).

Figures

FIGURE 1. Ololygon skuki (CFBH 47968, male topotype, SVL 14.7 mm). (A) Dorsal and (B) ventral views of the body. (C) Right hand and (D) right foot in ventral view. (E) Head in lateral view. Scales = 1 mm.

FIGURE 2. Nuptial pad on fingers II and III of the left hand of the topotype specimen of Ololygon skuki (CFBH 47968, male). Hand in (A) ventral and (B) dorsal (digitally reversed) views. The arrow indicates the glandular acini of the nuptial pad on Finger III. Scales = 0.2 mm.

FIGURE 3. Male topotypes of Ololygon skuki in life. Body in (A) dorsolateral, (C) dorsal, (D) ventral, and (E) lateral views of CFBH 47968 (male, SVL 14.7 mm). Body in (B) in dorsolateral view of MHNUFAL 12390 (male, SVL 15.3 mm). (F) Body in posterodorsal view showing the hidden posterior surfaces of thighs and shanks of CFBH 47968. Photo (B): João Almeida.

FIGURE 4. Vocalization of Ololygon skuki (MHNUFAL-SOM 001; unvouchered specimen). (A) Oscillogram (above) and spectrogram (below) of one call. (B) Oscillogram (above) and spectrogram (below) of two notes in the red brackets of (A). (C) Expanded oscillogram of the first note of (B).

FIGURE 5. Phylogenetic relationships of the Ololygon argyreornata group as recovered in one of the 2,450 most parsimonious trees obtained from the analysis of molecular dataset with gaps as a fifth state under equal weights for all transformations. All nodes shown are retained in the strict consensus. Values around nodes are parsimony jackknife supports. An asterisk (*) indicates lineages with 100% jackknife frequencies. Nodes lacking values have <50% jackknife support. See Araujo-Vieira et al. (2023: appendix S1) for the list of GenBank accession numbers and localities.

FIGURE 6. Known geographic distribution of Ololygon skuki. The white star indicates the type locality in Mata do Catolé, municipality of Maceió, state of Alagoas. The white dot indicates the new record for the state of Bahia in the municipality of São Sebastião do Passé. We only consider records with voucher specimens in collections.

FIGURE 7. (A–C) Couples of Ololygon skuki in amplexus in Mata do Catolé, Maceió, state of Alagoas, Brazil. (D) Interspecific amplexus between a male of Chiasmocleis alagoana and a female of O. skuki. Photos: Bruno Vilela.