Eleutherodactylus franzi sp. nov.

Gruenwald, Christoph I., Montano-Ruvalcaba, Carlos, Jones, Jason M., Ahumada-Carrillo, Ivan, Gruenwald, Andre J., Zheng, Jiacheng, Strickland, Jason L. & Reyes-Velasco, Jacobo, 2023, A novel species of piping frog Eleutherodactylus (Anura, Eleutherodactylidae) from southern Mexico, Herpetozoa 36, pp. 95-111 : 95

Eleutherodactylus franzi sp. nov.

Figs 2 , 3 , 4 , 5A Franz’s Piping Frog / Rana gaitera de Franz

Type material.

Holotype. INIRENA 2900 (CIG 01725). Adult male (Fig. 2 ), El Cucharillo, Municipio de Ixcateopan de Cuauhtémoc (18.5331, -99.7335, 2,315 m a.s.l.; datum = WGS84), Guerrero, Mexico, collected on 27 June 2020 by Héctor Franz-Chávez, Christoph I. Grünwald, André J. Grünwald and Kimberly Montelongo-Chávez. Paratypes (n = 14; Fig. 3 ). INIRENA 2901--10 (CIG 01716-24, 01726), 10 adult males, collected at same locality and on same date as holotype; INIRENA 2895--97 (CIG 01727-29), 3 adult males, 3 km E of Ixcateopan de Cuauhtémoc, Municipio de Ixcateopan de Cuauhtémoc (18.5076, -99.7329, 2,060 m a.s.l.; datum = WGS84), Guerrero collected on 27 June 2020 by Héctor Franz-Chávez, Christoph I. Grünwald, André J. Grünwald and Kimberly Montelongo-Chávez; INIRENA 2898 (CIG 01731), 1 adult male, between El Cucharillo and Chichila, Municipio de Taxco de Alarcón, (18.5335, -99.7117, 2,260 m a.s.l.; datum = WGS84), Guerrero, Mexico, collected on 27 June 2020 by Héctor Franz-Chávez, Christoph I. Grünwald, André J. Grünwald and Kimberly Montelongo-Chávez.

Diagnosis.

Based on our phylogenetic analysis, this is a member of the genus Eleutherodactylus , subgenus Eleutherodactylus Syrrhophus , as defined by Hedges et al. (2008). In the Eleutherodactylus (Syrrhophus) nitidus species series and the Eleutherodactylus (Syrrhophus) nitidus species group as defined by Grünwald et al. (2018), based on the condition of the tympanic annuli, ventral epidermis and visceral peritoneum. A small frog, but relatively large Syrrhophus , adult males measure 25.6-29.5 mm SVL; vocal slits are present in males, readily visible under partially translucent ventral epidermis; digital tips are widely expanded, 1.8-2.6 times the width of the narrowest part of the finger on the third and fourth fingers; fingers moderately long, finger lengths are I-II-IV-III with third finger length ranging from 15-18% of SVL; compact lumbo-inguinal gland above the inguinal region present, raised, indistinct, but visible in live specimen; ventral epidermis is partially translucent and visceral peritoneum is clear, not white, thus abdominal vein is not clearly visible against a white background on the venter of live specimens and viscera is partially visible through translucent dark grey ventral epidermis; limbs moderate, TL/SVL ratio is 0.40-0.50, FeL/SVL ratio is 0.31-0.38 and TotFL/ SVL ratio is 0.50-0.60; snout relatively short, END/ SVL ratio is 0.08-0.11; tympanum small, indistinct and round, tympanic annuli not visible in live specimen; TW/ED ratio is 0.40-0.60. The dorsal and lateral skin is slightly shagreened, whereas the ventral skin is smooth. Dorsal colouration cream or tan, with darker brown reticulations on dorsal and lateral portions of head and back; loreal and region dark brown, from snout to behind tympanum, with some pale spots and speckling present on labial region same colour as pale dorsal colouration; pale interorbital bar variable, may be present or absent, when present same colour as pale dorsal colouration of head and body; distinct irregular-edged dark brown transverse bands present on legs; upper arms same colouration and pattern as forearms; no pale mid-dorsal stripe; upper flanks same colour as dorsum, lower flanks whitish with some grey marbling; venter pale lavender with some sparse white spotting and pale grey on throat. No inguinal flash colours present on thighs and groin. The mating call of adult males is a short low-pitched pipe (see below; Fig. 4 ).

Comparisons.

Eleutherodactylus franzi can be distinguished from all species in the Eleutherodactylus (Syrrhophus) longipes species series by: possessing a small, indistinct tympanum with no tympanic annulus visible and with a diameter less than 50% of the diameter of the eye; by possessing a ventral epidermis which is semi-translucent and combined with a visceral peritoneum which is not white, an abdominal vein on the venter is not clearly evident against a white background in life; by possessing indistinct, but visible raised lumbo-inguinal gland above the inguinal region.

Eleutherodactylus franzi can be distinguished from most species of the Eleutherodactylus (Syrrhophus) modestus species group by the combination of possessing a compact, protruding lumbo-inguinal gland above the inguinal region, digital tips which are expanded more than 1.8 times the width of the narrowest part the finger on the third and fourth fingers and the lack of a distinct interorbital bar a colour distinct from the dorsal ground colouration. It can further be distinguished from the superficially similar E. grunwaldi by its smaller body size, 25.6-29.5 mm (vs. 28.4-32.4 mm), less expanded fingertips, 1.8-2.5 times the width of the narrowest part of the finger on fingers three and four (vs. 2.8-3.2) and the presence of a visible raised lumbo-inguinal gland. From the superficially very similar E. saxatilis , it can be distinguished by snout shape, eye size and head colouration. These two frogs, although not closely related, are very similar in appearance, but come from two widely-separated mountain ranges in central Mexico and are genetically distinct. Eleutherodactylus franzi has an angular canthus rostralis, with a shorter snout that is distinctly truncated from a lateral profile. It has a larger eye, with a larger ETD and, generally, there is a pale interorbital region that lacks dark markings. In E. saxatilis , the canthus rostralis is noticeably rounded and the snout is acuminate from a lateral profile. The eyes are smaller and located closer to the tympanum and there is no noticeable lack of dark dorsal markings in the interorbital area.

Within its own species group, E. franzi can be distinguished from most species by possessing a compact inguinal gland that is indistinct, but visible in live specimens. This character may or may not be visible in preserved specimens depending on how they were preserved. This species differs from E. pipilans , E. erythrochomus and E. nebulosus , which lack visible compact lumbo-inguinal glands altogether. All other known species in the E. (Syrrhophus) nitidus species group have readily visible compact lumbo-inguinal glands above the inguinal region, except E. maculabialis , which has similarly visible, but indistinct lumbo-inguinal glands. Eleutherodactylus franzi can be further distinguished from E. pipilans and E. nebulosus by possessing digital tips which are expanded more than 1.8 times the width of the narrowest part of the finger and from E. erythrochomus by possessing digital tips which are more than 1.5 times, but less than 3.0 times, the width of the narrowest part of the finger. It is distinguished from E. albolabris , E. nitidus , E. petersi , E. jamesdixoni and E. orarius by the combination of larger size, smoother skin, longer limbs and tips of digits which are expanded more than 1.8 times the narrowest part of the finger on the third and fourth fingers. This species is distinguished from E. dilatus , E. humboldti , E. maurus and E. sentinelus by its larger size, smoother skin, pale dorsal colouration with dark reticulations and lack of a pale interorbital bar which is paler than the pale dorsal colouration. Furthermore, all these species, except E. humboldti , present multi-note whistles, while E. franzi has a call that consists of a single note, low-pitched pipe. Eleutherodactylus franzi may be distinguished from E. maculabialis and E. syristes by its larger size, more expanded fingertips, lack of inguinal flash colouration, as well as those species’ unique advertisement call which consists of a trill rather than a short pipe. In Guerrero, two other species of saxicolous Eleutherodactylus ( E. pipilans and E. erythrochomus ) have similar colouration, similar smooth skin and widely expanded digital pads. Both are readily distinguishable from E. franzi by possessing an indistinct lumbo-inguinal gland which is barely visible in life and by a male advertisement call which is a peep instead of a pipe. Furthermore, E. franzi can be distinguished from E. pipilans by its more expanded digital tips on the third and fourth fingers, 1.8-2.5 times the width of the narrowest part of the finger (vs. 1.3-1.9) and distinct lack of dark markings in the interorbital region (vs. no difference from rest of dorsum). It can further be distinguished from E. erythrochomus by the conspicuous dark pattern on a pale dorsal colouration, lesser expanded digital tips no more than 2.5 times the width of the narrowest part of the digit on the third and fourth fingers (vs. 2.3-3.8) and a less distinct tympanum. General characteristics for the Eleutherodactylus nitidus species group are given in Table 1 .

Description of the holotype.

Adult male, relatively large (26.2 mm SVL); head as wide (9.5 mm) as long (9.5 mm), head wider than body; snout rounded from a dorsal view and rounded to slightly truncate from a lateral profile; tympanum indistinct, rounded with no supra-tympanic fold present; tympanum small, oval, greatest width of tympanum 1.4 mm; greatest diameter of eye 2.8 mm; tympanum width to eye-diameter 0.51; eyelid width 1.6 mm, approximately 38% of the IOD; first finger shorter than second finger; finger lengths from shortest to longest I-II-IV-III; digital pads on fingers two, three and four expanded, 2.1 times the narrowest point of the digit on fingers three and four; expanded finger pads widely expanded, truncate, three palmar tubercles; inner palmar tubercle 70% of middle palmar tubercle and outer palmar tubercles about 60% as large as middle palmar tubercle, (Fig. 5A ); toe lengths from shortest to longest I-V-II-III-IV, TL1 and TL5 very similar; outer metatarsal conical with a round base moderate, approximately 56% of inner metatarsal tubercle; inner metatarsal tubercle spherical shape with oval base, large, approximately 1.1 mm in length. Dorsal skin smooth, lateral skin slightly shagreened with some low tubercles; ventral skin smooth. Vocal slits present.

In life, the holotype had a yellowish-tan dorsal colouration on the back, with darker brown blotches on the back and flanks. Head yellowish-tan with some dark brown speckling, no pale interorbital bar; however, the interorbital region mostly lacks darker brown speckling giving it the resemblance of a pale interorbital bar. Labial region pale grey with some tan and some white speckling. Three and four white-tipped tubercles present at the rictal. A dark brown stripe present from the tip of the snout posteriorly through loreal region, eye and tympanum to right above rictal tubercles. Forearms, thighs, femur and tarsus tan with indistinct pale brown banding. The upper arms were unmarked, tan to slightly orange. No inguinal flash colouration was present on groin or thighs. Ventral colouration was lavender with some sparse white and on sides, ventral colouration on throat grey. Ventral skin was slightly translucent and visceral peritoneum clear, so no visible red abdominal vein and viscera were visible in life.

Colouration in preservative is pale tan on dorsum, with darker brown reticulations. Pale tan interorbital bar present. Dark canthal bar is dark brown. Unmarked upper arms are cream to white. Limbs cream with dark brown cross-banding. The dorsal surfaces of the legs are light brown and the groin and posterior surfaces of the thighs are brown. Ventral surfaces yellowish-cream, unmarked, slightly darker brownish pigmentation on throat and chin. Ventral surfaces of hands and feet brown, with dark brown spots. (Fig. 2D, E ).

Measurements of the holotype (in millimetres).

IND 2.2, IOD 4.2, END 2.5, ETD 0.9, UpL 6.4, FoL 7.5, PaL 2.3, HaL 6.7, F1L 2.3, F1PW 0.5, F1W 0.4, F2L 2.8, F2PW 0.8, F2W 0.4, F3L 4.7, F3PW 1.1, F3W 0.5, F4L 3.5, F4PW 1.1, F4W 0.5, IPTL 0.7, MPTL 1.0, OPTL 0.6, FeL 10.0, TL 11.0, TaL 7.1, TotFL 11.4, T1L 2.4, T1PW 0.62, T1W 0.5, T2L 3.6, T2PW 0.7, T2W 0.5, T3L 4.4, T3PW 0.7, T3W 0.5, T4L 6.0, T4PW 0.7, T4W 0.5, T5L 2.5, T5PW 0.6, T5W 0.4, IMTL 1.1, OMTL 0.6, FeL/SVL 38%, TL/SVL 42%, HaL/SVL 26%, TotFL/SVL 56%, HL/SVL 35%, HW/SVL 36%.

Variation.

SVL from 25.6-29.5 mm (27.15 ± 1.77). Expanded finger pads vary from 1.8-2.5 times the narrowest part of the digit on the third finger and from 1.8-2.6 times the narrowest part of the digit on the fourth finger, with average 2.0 ± 0.21 on the third finger and average 2.2 ± 0.21 on the fourth finger. Dorsal ground colouration cream or tan, but varied with some greenish, reddish or yellowish tinge, always with darker brown blotches or reticulations. The extent of the darker brown blotches or reticulation varied greatly. The condition of the interorbital area ranged from unmarked and same colour as ground colouration to heavily marked by dark speckling same colour as dark dorsal blotches or reticulation. Venter always lavender, but with varying amounts of white spots. Morphological variation of E. franzi is presented in Table 2 .

Advertisement call.

The advertisement call of the males of this species consists of a single, short, low-pitched pipe that lasts about 106 ms and has a dominant frequency of 2612.7 ± 40.6 Hz (Fig. 4A-D ). The note has limited amplitude modulation and the highest energy is displayed at the end of the note. The call is similar to that of E. pipilans and E. erythrochomus . The call differs from the nearby E. maurus and the sympatric E. humboldti , which also have a pipe, by being shorter and lower pitched. We present call data for both E. franzi and the sympatric E. humboldti in Table 3 . The advertisement call also differs from the sympatric or near sympatric E. petersi and E. nitidus as these two species have a call that consists of a multi-note whistle rather than a single-note pipe.

Distribution and ecology.

Eleutherodactylus franzi appears to be endemic to the Sierra de Taxco Region of northern Guerrero (Fig. 6 ). This is an extension of the Mexican Transverse Volcanic Belt which extends south into the Balsas Basin. This frog occurs at high elevations between 2,000-2,400 m a.s.l. and has been collected in tropical deciduous forest, oak woodland and pine-oak forest, as well as mixtures of these assemblages. It is restricted to areas of karstic rock outcroppings and the associated sinkholes and caves systems. This species may also occur in nearby Estado de México, as habitat is continuous and the State line is near the type locality. Old reports of E. pipilans from that State may be referable to this species; however, we have made attempts to examine these specimens at MZFC and were not able to find the specimens (C. Grünwald, pers. obs.)

Etymology.

This species is named after Héctor Franz-Chávez, Mexican herpetologist and avid field collector who collected the type material and who helped collect an extensive sampling of the Eleutherodactylus specimens to be used in our succession of studies.

Figures

Figure 2. Holotype of Eleutherodactylus franzi, sp. nov., INIRENA 2900 (CIG 01725), El Cucharillo, Municipio de Ixcateopan de Cuauhtemoc, Guerrero, Mexico in life (A-C) and in preservative (D, E).

Figure 3. Some of the paratypes of Eleutherodactylus franzi sp. nov., in life. A-C. INIRENA 2902 (CIG 01717) El Cucharillo, Municipio de Ixcateopan de Cuauhtemoc, Guerrero, Mexico; D-F. INIRENA 2910 (CIG 01726) El Cucharillo, Municipio de Ixcateopan de Cuauhtemoc, Guerrero, Mexico; G-I. INIRENA 2895 (CIG 01727), 3 km E of Ixcateopan de Cuauhtemoc, Municipio de Ixcateopan de Cuauhtemoc, Guerrero, Mexico; J-L. INIRENA 2896 (CIG 01728), 3 km E of Ixcateopan de Cuauhtemoc, Municipio de Ixcateopan de Cuauhtemoc, Guerrero, Mexico; M-O. INIRENA 2898 (CIG 01731), between El Cucharillo and Chichila, Municipio de Taxco de Alarcon, Guerrero, Mexico.

Figure 4. Spectrograms (top) and oscillograms (bottom) of the advertisement calls of Eleutherodactylus franzi sp. nov., recorded at El Cucharillo, Municipio de Ixcateopan de Cuauhtemoc, Guerrero, Mexico (A, B) and at 3 km E of Ixcateopan de Cuauhtemoc, Guerrero, Mexico (C, D).

Figure 5. A. Ventral aspect of the hand of the holotype of Eleutherodactylus franzi sp. nov., INIRENA 2900 (CIG 01725) from El Cucharillo, Municipio de Ixcateopan de Cuauhtemoc, Guerrero, Mexico; B. Ventral aspect of the hand of a Eleutherodactylus humboldti, INIRENA 2911 (CIG 01703) from 9.4 km N of Valle de Bravo junction on Valle de Bravo - Toluca toll road, near San Bartolo, Municipio de Amanalco, Estado de Mexico, Mexico.

Figure 6. Map showing the type localities and distribution of Eleutherodactylus which are either closely related or superficially similar to the species described herein from southern Mexico. White diamond represents the type locality of E. franzi sp. nov. and white circle represents additional locality.