Sibon ayerbeorum, Vera-Pérez, 2019

Vera-Pérez, Luis Enrique, 2019, A new species of Sibon Fitzinger, 1826 (Squamata: Colubridae) from Southwestern Colombia, Zootaxa 4701 (5), pp. 443-453 : 444-449

Sibon ayerbeorum sp. nov.

Figs. 1–5A .

Sibon cf. lamari: Ayerbe et al. (2007) .

Proposed common name: The Ayerbes’ snail-eater (Caracolera de los Ayerbe in Spanish)

Holotype. MHNUC-He-Se-000659 (field number LVP 0379; Figs. 1A , 2A , 3B and 4 C-D), adult female collected by Luis Enrique Vera Pérez on October 18, 2017, at sector La Cueva , Parque Nacional Natural Munchique, municipality of El Tambo, department of Cauca, Colombia (2º46’15.6’’ N, 76º58’48.6’’ W, 1135 m).

Paratypes (N=3). MHNUC-He-Se-000660 (field number LVP 0380; Figs. 1B , 2B , 3A , 4 A-B and 5A), adult female collected by Luis Enrique Vera Pérez on October 19, 2017, at same locality as holotype (2º46’14.6’’ N, 76º58’44.3’’ W, 1191 m). MHNUC-He-Se-000360, 000361 (field numbers: CSA-00248-se, 00249-se), male and female juveniles, respectively, collected on June 15–16, 1988, at San Joaquín River , La Playa , Parque Nacional Natural Munchique , municipality of El Tambo, department of Cauca, Colombia (1400 m) by Óscar Mosca Castillo .

Diagnosis. Sibon ayerbeorum differs from all other congeners based on the following combination of characters: (1) 15–15–15 (N=3) or uncommonly 15–17–15 (N=1) smooth DSR without enlarged vertebral row; (2) preoculars absent; (3) non-protuberant eyes; (4) six supralabials with 3 th to 5 th (N=6) or 3 th and 4 th (N=2) contacting orbit; (5) six infralabials with 1 st to 4 th in contact with anterior chinshields, (6) first pair of infralabials generally in contact behind symphysial (N=3); (7) postmental absent; (8) 155 ventrals in the single male, 136–140 in females; (9) 93 paired subcauldals in the single male, 78–79 in females; (10) 248 ventrals plus subcaudals in the single male, 214–219 in females; (11) 15.6 mm SVL in the single male, 13.6–29.3 mm in females; (12) 6.5 mm TL in the single male, 5.9–12.4 mm in females; (13) body coloration pattern composed by irregular middorsal and ventrolateral dark-bordered ocelli; (14) ventral coloration dark with light spots in each ventral scale.

Comparisons ( Table 1 ). Sibon ayerbeorum is more similar to species of the S. argus group, with which it shares an ocellate pattern, 15–15–15 DSR, loreal contacting eye, enlarged penultimate supralabial bordering the orbit and the ratio of tail length (28–33% of total length). However, it differs by having fewer ventrals, subcaudals, ventrals plus subcaudals and non-protuberant eyes with respect to S. argus (protuberant eyes); and fewer ventrals, subcaudals and ventrals plus subcaudals in the single male and females, only six supralabials, and postmental absent with respect to S. longifrenis (usually a tiny postmental). Additionally, it is smaller (maximum TOL= 417 mm) than S. argus (more than 690 mm) and S. longifrenis (700 mm).

The new species can be easily differentiated from species of the S. annulatus and S. nebulatus groups because they present a regularly blotched/banded pattern or an irregular pattern with small blotches, spots, and stipples. In addition, the new species has fewer ventrals, supralabials, infralabials and an absence of postmental scales when compared with S. lamari . In relation to its congeners distributed in Colombia, S. ayerbeorum has fewer ventrals and subcaudals than S. annulatus ; and fewer ventrals and ventrals plus subcaudals in males and females than S. nebulatus , as well as the absence of postmental scales (present in S. annulatus ).

Description of holotype. Adult female is based on the presence of eggs in the posterior portion of body, TOL 417 mm, SVL 293 mm, TL 124 mm (29.7% of TOL). Head is longer (HL 13.2 mm) than wide (HW 7.9 mm) and distinct from neck; snout short (SL 3.0 mm), blunt in dorsal and lateral view; rostral not extending posteriorly between internasals, wider (1.6 mm) than high, same length than median internasal suture (0.9 mm); internasals slightly shorter (0.9 mm) than wide (1.1 mm), their length about three-fourths length of prefrontal suture (1.2 mm); prefrontals as long (2.0 mm) as wide (1.9 mm), bordering the eye above loreal, their median suture (1.6 mm) about three-sevenths length of frontal; frontal longer (3.7 mm) than wide (2.4 mm), widest anteriorly, length almost twothirds that of parietals, in contact with prefrontals, supraoculars and parietals; supraoculars longer (3.0 mm) than wide (1.8), widest posteriorly; parietals longer (5.6 mm) than wide (3.3 mm), widest anteriorly, their suture (4.1 mm) about nine-tenth length of frontal; parietals in contact with frontal, supraoculars, upper postoculars, anterior and posterior temporals and six nuchal scales; nasal divided, longer (1.7 mm) than high (0.9 mm), in contact with rostral, prefrontals, loreal and first two supralabials; loreal single, longer (1.4 mm) than wide (0.9 mm), its length one-half length of eye (2.7 mm); pupil semi-elliptical; no preocular; three postoculars; two anterior temporals (low- er small in right side), 3/2 posterior temporals, temporals above fifth supralabial; six supralabials, 3 rd to 5 th bordering the eye; penultimate supralabial enlarged; six infralabials, 1–4 in contact with anterior chinshields, first pair in contact behind mental; no postmental; anterior pair of chinshields longer (3.0 mm) than wide (1.2 mm), longer than posterior pair; posterior pair of chinshields longer (2.4 mm) than wide (1.4 mm), slightly wider than anterior pair; mental groove present; 139 ventrals; cloacal plate single; supracloacal ridges absent; 79 paired subcaudals; dorsal scales smooth in 15–15–15 rows without apical pits; vertebral row not enlarged. Body is compressed laterally. Middorsal ocelli absent on anterior portion of body, appearing small on the 2 / 5 portion and increasing in size towards the posterior portion of body and tail; ocelli color is just present scarcely on parietals. Ventrolateral ocelli absent, diffuse or small up to 1 / 3 portion of body. Dark venter with one enlarged or two small light spots appear on almost all ventral scales. Maxillary teeth 18/19, 1 st and 2 nd of each maxilla are less separated in relation to the others.

Variation. Most differences with holotype are present in the juvenile paratype MHNUC-He-Se-000361, which has 15–17–15 DSR and the enlarged penultimate supralabial separated from orbit in both sides by the presence of a small subpostocular (right side) and by elongation of the antepenultimate supralabial that reaches the lower postocular (left side). A projection of the posterior margin of mental scale is present in paratypes MHNUC-He-Se-000660 and 000360, blocking the contact between first pair of infralabials in the last one. Morphological characters of the type series of Sibon ayerbeorum is shown in Table 2 .

Coloration in life ( Figs. 3–5A ). Dorsal ground color tan to burly wood, with chocolate to sienna middorsal and ventrolateral ocelli bordered of medium taupe to dark taupe. Most dorsal scales are spotted and/or tipped mainly with the same ocelli border color. Interspaces color between ventrolateral ocelli are white to ivory, which is replaced progressively by dorsal ground color from anterior to posterior portion of body and tail. Upper surface of head colored mainly with the ocelli border color, dorsal ground color and scarcely stippled with the ocelli color. Lower surface of the head is colored mainly with the same colors as lateral ocelli interspaces and the ocelli borders, spotting the chinshields, gular and preventral scales and forming sutures on labials. Ventral coloration composed mainly of the same color as ocelli borders and white spots. Eyes golden rod and pale golden rod with dark spots, speckles and reticulations.

Color in alcohol. Coloration in preservative is similar to that in life after a year, except that the dorsal ground and ocelli colors that have slightly faded. On the specimens collected 30 years ago the ocelli border color became light brown, dorsal ground color is pinkish, white coloration is pale cream and ocelli are pale orange.

Natural history. Sibon ayerbeorum occurs at highly conserved habitats of humid premontane forest and the transition toward tropical humid forest. At type locality, individuals were found active at night (22:30, 23:30 h) moving on the ground (holotype) and foraging on vegetation about 1.5 m above ground ( Fig. 4A ). The defensive behavior upon the capture of paratype consisted of an expansion of head simulating a triangular shape, followed by a dorso-ventral compression and a body coiling forming a flattened dorsal posture ( Fig. 4B ). Then, it expelled foul odors by anal gland secretions and fecal wastes, and finally, it turned around to sit still in ventral position to look like a dead snake. During handling for taking pictures during the day, the holotype hid its head forming a “cinnamon roll” or body knot shape ( Fig. 4 C-D).

Both adult females were gravid, each one with two well-formed eggs perhaps about to be deposited due to their proximity to the cloaca. The new species inhabits in sympathy with other tree snail-eating snakes ( Vera-Pérez et al. 2018): Sibon nebulatus , Dipsas sanctijoannis and D. temporalis ( Fig. 5 ).

Geographic distribution. This species is endemic to Colombia and only known from the Western slopes of Western Cordillera in La Cueva and La Playa, Parque Nacional Natural Munchique, municipality of El Tambo, department of Cauca ( Fig. 5 ) at elevations between 1135 and 1400 m. The distance between the two localities is approximately 10 km in a straight line.

Remarks. Coordinates for “La Playa”, Parque Nacional Natural Munchique were taken from Ayerbe et al. (2007) from other specimens collected in that locality at the same altitude.

Etymology. Named in honor of Santiago Ayerbe González and his sons Fernando and Santiago José (R.I.P). Dr. Ayerbe is a renowned Colombian pediatrician and toxinologist who has devoted most of his life in favor of prevention, treatment and management of snakebites, and has also contributed to the knowledge of the reptiles of the department of Cauca. Fernando is a renowned ornithologist and scientific illustrator, author of the most recent book about the birds of Colombia. Santiago José died in the earthquake which affected the city of Popayán in March, 1983.

Conservation status. Several areas among the Colombian Pacific region have had little or no sampling, including a great extension of Parque Nacional Natural Munchique. In addition, the capture of the juvenile paratypes by a local person and the lack of coordinates make possible the occurrence of this species not only into the protected area, but also in surrounding and buffer areas. For these reasons, I consider that the new species is still poorly known, especially regarding its geographic distribution, habitat preferences and population. So, it can be listed as Data Deficient according the IUCN guidelines.

Figures

FIGURE 1. Holotype MHNUC-He-Se-000659 (A) and paratype MHNUC-He-Se-000660 (B) of Sibon ayerbeorum in dorsal (top) and ventral (middle) views, and a portion after midbody (bottom: dorsal, lateral and ventral views, respectively). Scale bars = 5 cm.

FIGURE 2. Heads of holotype MHNUC-He-Se-000659 (A) and paratype MHNUC-He-Se-000660 (B) of Sibon ayerbeorum in dorsal, lateral (right, left) and ventral views (from top to bottom, respectively). Scale bars = 1 cm.

FIGURE 3. Coloration in life of adults paratype MHNUC-He-Se-000660 (A) and holotype MHNUC-He-Se-000659 (B) of Sibon ayerbeorum.

FIGURE 4. Paratype MHNUC-He-Se-000660 of Sibon ayerbeorum foraging on vegetation (A) and forming a flattened and coiled posture upon capture (B), and holotype MHNUC-He-Se-000659 hiding its head during the day (C-D).

FIGURE 5. Snail-eaters from Parque Nacional Natural Munchique: (A) Sibon ayerbeorum (paratype MHNUC-He-Se-000660), (B) Sibon nebulatus (MHNUC-He-Se-000656), (C) Dipsas sanctijoannis (not collected), and (D) D. temporalis (MHNUC-He- Se-000654).

Tables

TABLE 1. Comparative summary of characteristics of Sibon ayerbeorum, similar species and congeners distributed in Colombia. Abbreviations of characters are presented in Material and methods. Dashes in DSR separate the anterior, midbody and posterior counts. Values in italics indicate incomplete tails. Based and complemented from Lotzkat et al. (2012).

	S. ayerbeorum	S. argus	S. longifrenis	S. lamari	S. annulatus	S. nebulatus
TOL max (mm)	417	690	700	592	733	1013
M	221		578	592	733	738
F	417		541	544	576	1013
Ventrals
M	155	181–201	166–173	168–171	170–197	159–200
F	136–140	186–192	147–168	162–163	161–186	161–193
Subcaudals
M	93	112–121	95–106	112–119	104–133	75–114
F	78–79	95–108	80–101	77–108	107–124	64–100
Ventrals + subcauldals
M	248	294–322	263–275		278–318	262–289
F	214–219	281–300	231–263		277–304	247–279
DSR	15–15–15, 15– 17–15	15–15–15	15–15–15	15–15–15	15–15–15	15–15–15
Preoculars	Absent	Absent	Usually absent	Usually absent	Usually absent	Usually absent
Postoculars	2–3	2–3	1–3	2	0–2	1–4
Tant	1–2	1–2	1–2	1	1–2	1
Tpost	2–3	2–3	1–3	2–3	1–3	1–2
Supralabials	6	6–9	7–9	7–8	6–9	5–9
Infralabials	6	6–9	6–9	8–10	6–10	6–10
1st infralabials behind mental	Usually in contact	Usually separated	Separated	Separated	Separated	In contact
Postmentals	0	0	0–1	2	1–2	0

TABLE 2. Measurements and counts in the type series of Sibon ayerbeorum. Abbreviations of characters are presented in Material and methods. Oblique bar separates the right/left sides when counts are different. Numbers in parentheses represent supralabials and infralabials in contact with the orbit and anterior chinshields, respectively.

	Holotype MHNUC- He-Se-000659	Paratype MHNUC- He-Se-000660	Paratype MHNUC- He-Se-000360	Paratype MHNUC- He-Se-000361
SEX	F	F	M	F
SVL (mm)	293	272	156	136
TL (mm)	124	113	65	59
Ventrals	139	136	155	140
Subcaudals	79	78	93	79
DSR	15–15–15	15–15–15	15–15–15	15–17–15
Preoculars	Absent	Absent	Absent	Absent
Postoculars	3	2	3	3/2
Tant	2	2	1/2	1/2
Tpost	3/2	3	2	3
Supralabials	6(3–5)	6(3–5)	6(3–5)	6(3, 4)
Infralabials	6(1–4)	6(1–4)	6(1–4)	6(1–4)
1st infralabials behind mental	in contact	in contact	separated	in contact
Postmentals	0	0	0	0
Maxillary teeth	18/19	16/17	20/19	20