Bolitoglossa silentium, Arias & Chaves & Kubicki & Parra-Olea, 2024

Arias, Erick, Chaves, Gerardo, Kubicki, Brian & Parra-Olea, Gabriela, 2024, Taxonomic assessment of the Bolitoglossa (Eladinea) subgenus (Caudata: Plethodontidae) with the description of two new species from the Cordillera de Talamanca, Costa Rica, Zootaxa 5537 (2), pp. 211-233 : 224-228

Bolitoglossa silentium sp. nov.

http://zoobank.org/ urn:lsid:zoobank.org:act:79090380-9E6A-4E8E-995D-9D90097AD705

Valle del Silencio Web-footed Salamander

( Figures 8–10 )

Holotype. UCR20489 ( Figs. 8–9 ), an adult male from Costa Rica: Provincia de Limón: Cantón de Talamanca: Distrito de Telire: Valle del Silencio Biological Station , Parque Internacional La Amistad , (9.1093º N, - 82.9625º W, 2450 m elevation), collected by Gerardo Chaves, Adrián García-Rodríguez, and Luis Guillermo Artavia on 10 July 2008.

Paratypes. UCR21203, a subadult male; same locality as holotype, collected by Eduardo Boza-Oviedo on 4 April 2011 .

Generic Placement. Assigned to the genus Bolitoglossa due to having fewer than 14 costal grooves and lacking a sublingual fold and to the subgenus Eladinea based on the molecular evidence presented herein.

Diagnosis. The combination of the following characteristics can be used to distinguish Bolitoglossa silentium from the other described species of the genus Bolitoglossa : (1) moderate species (55.9 mm in adult male) with limbs relatively long and slender; (2) head relatively long; (3) hands and feet greatly unwebbed, at least two phalanges of the longest digits free of webbing; (4) dorsal coloration dark brown with large blotches yellowish green; gular surface paler that venter, yellow to yellowish green; (5) 16S and cyt b mtDNA distances.

Comparisons. Bolitoglossa silentium is differentiated from members of the subgenus Eladinea by its 16S and cyt b mtDNA distances. Since B. silentium is only known to occur in Costa Rica and molecular evidence strongly supports it forming part of the Bolitoglossa diminuta species group within the subgenus Eladinea , phenotypic comparisons are presented here only concerning to members of that clade (i.e., B. aurae , B. aureogularis , B. chiquitica sp. nov., B. diminuta , B. jugivagans , and B. pygmaea ), which are endemic to mountain ranges of Costa Rica and western Panama. In addition, we compare with B. robinsoni due the geographic proximity and the lack of information about the phylogenetic position of the last species.

Contrasting characteristics for Bolitoglossa silentium are presented in parentheses. Bolitoglossa aurae Kubicki and Arias 2016 can be distinguished from B. silentium by having unique dorsal coloration of pale yellow with a dark brown middorsal stripe on the head and body (dorsal color dark mustard yellow with extensive dark brown blotches); ventral surface brilliant yellow without evident dark blotches (ventral surface with extensive dark pigment); head shorter, FSL/SL = 26.2 % (FSL/SL = 31.5–32.6 %); adult smaller, SL = 40.5 mm (SL = 41.3–55.9 mm in adult males). Bolitoglossa aureogularis Boza-Oviedo et al. 2012 has limbs relatively short, LI = 3.5 (limbs longer, LI of 0–2); ventral coloration with extensive white pigment (ventral coloration dark brown with mustard yellow blotches); fingers and toes rounded (fingers and toes truncate); head shorter, FSL/SL = 25.6 % (FSL/SL = 31.5–32.6 %). Bolitoglossa chiquitica sp. nov. has hands and feet that are greatly webbed, with less than one phalanx of the longest digits free of webbing (hands and feet with little webbing, two phalanges of the longest digits are free of webbing); dorsal coloration yellowish cream to dark brown without evident dark blotches present (dorsal color dark mustard yellow with extensive dark brown blotches); adult smaller, SL = 25.2–28.8 mm (SL = 41.3–55.9 mm in adult males). Bolitoglossa diminuta Robinson 1976 by having dark midventral line (ventral coloration dark brown with mustard yellow blotches, without midventral line); fingers and toes rounded (fingers and toes truncate); adult smaller, SL = 31.1 mm (SL = 41.3–55.9 mm in adult males). Bolitoglossa jugivagans Hertz et al. (2013) has relatively short limbs, LI = 4 (limbs longer, LI = 0–2); dorsal coloration dark brown reddish (dorsal color dark mustard yellow with extensive dark brown blotches); fingers and toes rounded (fingers and toes truncate); head shorter, FSL/SL = 26.9 % (FSL/SL = 31.5–32.6 %); adult smaller, SL = 31.2 mm (SL = 41.3–55.9 41.3–55.9 mm in adult males). Bolitoglossa pygmaea Bolaños and Wake 2009 has hands and feet are greatly webbed, less than one phalanx of the longest digits free of webbing (hands and feet with little webbing, two phalanges of the longest digits are free of webbing); fingers and toes rounded (fingers and toes truncate); adult smaller, SL = 23.6–32.6 mm (SL = 41.3–55.9 41.3–55.9 mm in adult males). Bolitoglossa robinsoni Bolaños and Wake 2009 has the throat pale but with punctate melanophores (the gular surface is bright yellow with few dark melanophores); hands and feet longer than wide, HaL/HaW = 1.07±0.1, Fol/FoW = 0.94±0.08 (hands and feet wider than long, HaL/HaW = 0.85–0.88, Fol/FoW = 0.84–0.86); head shorter, FSL/SL = 30.1–31.4 % (FSL/SL = 31.5–32.6 %).

Description of holotype. Adult male having an SL of 55.9 mm ( Figs. 8–9 ). Head well-differentiated from the trunk (HeW 8.6 mm, NeW 6.2 mm, ShW 6.5 mm), with the greatest width of the head at an imaginary transverse line crossing the eyes; head truncate in dorsal outline and rounded to truncate in profile; snout moderate (SnL 4.1 mm, 7.33 % of SL), with nearly terminal small nostrils (LNH 0.5 mm, RNW 0.5 mm) directed anterolaterally; internarial area slightly concave in dorsal outline. Snout protruding beyond the anterior margin of the lower lip in lateral view. Eyes moderate to large (EW = 78 % of SnL), not protruding beyond the dorsal and ventral outline of the head, directed anterolaterally, with a distinct suborbital groove. Teeth are numerous. There are 4 premaxillary teeth, 61 maxillary teeth, and 24 vomerine teeth. Well-defined superior eyelids, barely higher than the top of the head in the interorbital area. Top of head flat and smooth, tapering slightly toward anterior terminus, lacking contrasting interorbital or other dermal structures. Canthus rostralis indistinct; intercanthal area flat to slightly convex; and loreal region slightly concave. Evident cirri (nasolabial protuberances) on tip of snout; nasolabial grooves start at ventrolateral margins of nares and terminate in a cirrus. Gular fold is well-defined, starting on the dorsolateral portion of the neck, below the postorbital groove. Evident mental gland is visible under the skin of the anterior intermandibular region, ovoid, 3.39 mm length in its larger diameter.

Arms relatively long and slender (FLL = 14.7 mm, 26.3 % of SL), without noticeable hypertrophied forearm compared to the upper arm. Hands relatively large and broad (HaL = 5.6 mm, 38.1 % of VGS; HaW = 5.2 mm, 60.5 % of HeW; Fig. 10A ). Finger I is embedded in the webbing tissue; tip of fingers II and IV with at least one phalanx protrude freely; two phalanges protrude free beyond interdigital tissue margin in Finger III. Tip of fingers truncate; terminal pads weakly discernible on the ventral surface of fingers II–IV. Relative lengths of fingers on the right hand I <IV <II <III.

Legs relatively long and slender (HLL 16.1 mm, 28.9 % of SL). Feet moderate and slender (FoL 6.4 mm, 43.5% of VGS; FoW 6.4 mm, 74.4 % of HeW; Fig. 10B ). Toes II, III, IV, and V protruding freely beyond interdigital tissue margin, Toe I with minimal indentation at webbing. Toe III is most free of interdigital tissue, with the two distal phalanges protruding. Tips of toes truncate; terminal pads discernible on ventral distal surface of toes II–V. Relative lengths of toes on the right foot I <V <II <IV <III.

Body subcylindrical (slightly wider than high) in cross-section, and slender (TW = 6.5 mm; TW = 23.7 % of AGL). The skin on the head, body, limbs, and tail surface is smooth. Eleven costal grooves are visible between the axilla and groin, 13 if counting axillary and inguinal grooves; costal grooves are most visible on ventral and lateral portions of the body. Adpressed limbs separated by 0 costal folds; 12 costal folds total between axilla and groin. Tail long (TL = 60.2 mm), cylindrical in cross-section, without an evident constriction at the base, and some caudal grooves discernible on anterior portion of the tail.

Coloration in life ( Fig. 8 ). The ground color of the dorsal surfaces of the head, trunk, tail, hind limbs, and forelimbs is dark mustard yellow with large dark brown blackish blotches. The dark blotches on the dorsum form a broad irregular dorsal band that extends from interorbital area to the anterior half of the trunk; two irregular lines extend from eye to anterior half of the body. This coloration extends to flanks, where dark mustard yellow is reduced to blotches on dark brown background. Head and upper eyelids have the same coloration of the trunk. The iris is bronze with a dark brownish-black reticulation. The ground coloration of upper surfaces of the arms and legs is similar to the color in trunk but few dark brown blotches are present. Tail coloration is the same to the trunk but with less dark blotches.

The trunk’s ventral surface is darker than the dorsal surface, dark bluish-black with numerous pale yellow mustard blotches. The chest was mustard yellow and paler in contrast when compared to the surrounding areas. Additionally, the chest nearly lacked the presence of dark melanophores. The gular surface is bright yellow with few dark melanophores; the mental gland is paler. The ventral surface of tail was similar to dorsal surface. The cloacal area was paler than the surrounding areas; dark mustard yellow. The ventral surfaces of the arms and legs were similar to the dorsal surfaces. The palmar and plantar surfaces were dark mustard yellow with black chromatophores.

Coloration in ethanol ( Fig. 9 ). After fifteen years in ethanol (70%) the overall coloration of the holotype has become darker throughout, principally consisting of a brown to dark brown tone. The dark mustard yellow of the trunk changed to pale brown generating a darker pattern in the trunk. However, the darker dorsal and lateral bands are still visible. The dorsal surfaces of limbs are pale brown. The trunk’s ventral surface is paler than in life, now being pale brown with dark and pale blotches. The gular surface is pale brown.

Measurements (in mm), limb interval, and percentages of the holotype. SL 55.9; TL 60.2; ShW 6.5; HeW 8.6; NeW 6.2; EW 3.2; SnL 4.1; JSL 9.6; LGFS 13.6; LNH 0.5; RNW 0.5; IND 3.1; NLP 0.9; ICD 3.9; HLL 16.1; FLL 14.7; TW 6.5; VGS 14.7; FSL 18.2; UHL 11.4; AGL 27.4; VL 5.5; HaW 5.2; HaL 5.6; LF2 3.1; LF3 3.9; WF3 1.4; FoW 6.4; FoL 6.4; LT2 3; LT3 3.6; WT3 1.3. Limb interval 0. Measurements in related percentages: VGS/SL 26.3 %; IND/HeW 36 %; AGL/SL 49 %; HeW/SL 15.4 %; HeW/AGL 31.4 %; SnL/ HeW 47.7 %; LNH/HeW 5.8 %; LNH/SL 0.9 %; RNW/HeW 5.8 %; RNW/SL 0.9 %; HLL/SL 28.8 %; FLL/SL 26.3 %; HaL/VGS 38.1 %; FoL/VGS 43.5 %; HaW/HeW 60.1 %; FoW/HeW 74.4 %; LT2/FoL 46.9 %; LF2/HaL 55.4 %; WT3/FoW 20.3 %; WF3/HaW 26.9 %. Number of teeth: PMT 4, MT 61, VT 24.

Variation. The paratype had a more rounded snout and much less defined protruding cirri or nasolabial protuberances, sexually dimorphic features. The paratype is darker than the holotype, with fewer mustard yellow coloration areas. In the paratype, the gular surface is darker than that of the holotype; however, it is paler than the venter of the trunk. In the paratype, the number of costal interspaces between adpressed limbs was 2, differing from the holotype (0). The tail was cut and the remaining tail was 27 mm.

Measurements (in mm), limb intervals, and percentages of the paratype. SL 41.3; ShW 4.4; HeW 5.9; NeW 4.5; EW 2.2; SnL 2.5; JSL 7.2; LGFS 10.7; IND 1.7; NLP 0.8; ICD 2.9; HLL 10.5; FLL 10; TW 4.5; VGS 9.9; FSL 13; UHL 6.8; AGL 20.7; VL 4; HaW 3.3; HaL 3.5; FoW 4.3; FoL 3.8. Limb intervals 2. Measurements in related percentages: VGS/SL 23.9 %; IND/HeW 28.8 %; AGL/SL 50.1 %; HeW/SL 14.3 %; HeW/AGL 28.5 %; SnL/HeW 42.4 %; HLL/SL 25.4 %; FLL/SL 24.2 %; HaL/VGS 35.4 %; FoL/VGS 38.4 %; HaW/HeW 55.9 %; FoW/HeW 72.9 %. Number of teeth: PMT 2, MT 42, VT 14.

Etymology. The specific epithet, silentium , is a noun in apposition and is from Latin, meaning silence. The Spanish meaning of silence is “silencio”, this name was chosen in recognition of the site where this species was found, Valle del Silencio (Silent Valley).

Habitat and natural history observations. The habitat of Bolitoglossa silentium is a mature cloud forest dominated by Quercus covered in moss, with a great abundance of bryophytes and epiphytes. The type locality occurs in the Montane rain forest ( Holdridge 1967; Bolaños et al. 2005), characterized by a very short dry season (one to two months), annual precipitation range between 2200 to 4500 mm, and annual temperature between 6 to 12 ºC. All specimens were found on the trunks of trees, active during the night.

Distribution. This species is known from the type locality, the Valle del Silencio and the Cerro Buru, at 2300–2450 m a.s.l. ( Fig. 1 ). This species was found in the primary forest within the protected area of La Amistad International Park.

Figures

FIGURE 1.A) Map of the Cordillera de Talamanca in the Costa Rica-Panamá border-line region showing all known populations of the seven species within the Bolitoglossa diminuta Species Group. B) Map showing the localities for B. bramei, B. pygmaea, B. robinsoni, and B. silentium sp. nov. on the Fábregas and Echandi massifs. The open shape indicates the historical data and the solid shape indicates the localities with molecular data included herein.

FIGURE 8. Holotype of Bolitoglossa silentium sp. nov. (UCR20489) in life. Photograph by Luis G. Artavia.

FIGURE 9. Dorsal and ventral views of the body of the holotype of Bolitoglossa silentium sp. nov. (UCR20489) in preservation. Photograph by E.A.

FIGURE 10. Ventral views of the hand and foot of the holotype of Bolitoglossa silentium sp. nov. (UCR20489) in preservation. Photographs by E.A.