Colostethus melanolaemus, GRANT & RODRÍGUEZ, 2001

GRANT, TARAN & RODRÍGUEZ, LILY O., 2001, Two New Species of Frogs of the Genus Colostethus (Dendrobatidae) from Peru and a Redescription of C. trilineatus (Boulenger, 1883), American Museum Novitates 3355, pp. 1-24 : 11-16

Colostethus melanolaemus , new species

Figures 6 , 8–11

HOLOTYPE: MUSM 17741 (field number AMNH FS 11921), an adult male collected by Lily O. Rodríguez, 11 March 1999, Explornapo Lodge , ACEER, Lower Río Napo near Quebrada Sucusari, Departamento Loreto, Peru, GPS coordinates 72°55'W, 3°14'S .

PARATYPES: MUSM 15607 , collected by Lily O. Rodriguez, 24 March 1993 at the type locality. AMNH FS 11920 and AMNH FS 11922 , collected by Lily O. Rodríguez, 10–11 March 1999 at the type locality. AMNH 114924–114945 , collected by Borys Malkin, 28 March–9 April 1970 at Estirón , Río Ampiyacu, Departamento Loreto, Peru .

ETYMOLOGY: The specific epithet is an adjective derived from the Greek melanos (black) and laemos (throat), in reference to the pure black throat of adult males of this species.

DIAGNOSIS: A small species (males to about 23 mm SVL, females to about 24 mm SVL); Finger III weakly swollen in adult males; throat black in adult males, immaculate white in females; testes white (unpigmented) in adult males; Toes II–IV basally webbed; dorsolateral stripe present; oblique lateral stripe present as a diffuse, inconspicuous, pale region or group of small spots that extends from the groin to midway along the flanks; ventrolateral stripe present (poorly defined); one subarticular tubercle on Finger IV; median lingual process absent; cloacal tubercles absent; anal sheath absent; black armband absent.

Colostethus melanolaemus is most similar to C. trilineatus and C. juanii . 6 It differs from both in having (1) throat pure black in adult males (gray in C. trilineatus ; gray stippling concentrated into spots, mottling, or reticulated pattern in C. juanii ), (2) significantly greater adult SVL ( tables 1, 2), and (3) weakly swollen Finger III in adult males (strongly swollen in C. trilineatus ; not swollen in C. juanii ). Colostethus melanolaemus further differs from C. trilineatus in having an advertisement call of 1–6 notes, mode = 4 (couplets or 9–13 notes, mode = 10, in C. trilineatus ), and emphasized frequency of 3840 – 4560 Hz (emphasized frequency 4920–6040 Hz in C. trilineatus ). Colostethus melanolaemus is further diagnosed from C. juanii in having significantly shorter internote duration ( C. melanolaemus : n = 11, range = 123.4–236.7, x = 153.15 ± 10.26 msec; C. juanii : n = 11, range = 271.9– 468.7 msec, x = 389.12 ± 18.89 msec; P = 0.0001).

MEASUREMENTS OF HOLOTYPE (in mm): The holotype, MUSM 17741, is an adult male with vocal slits and enlarged, white (unpigmented) testes. SVL 22.7; forearm length from proximal edge of palmar tubercle to outer edge of flexed elbow, 5.2; hand length from proximal edge of palmar tubercle to tip of Finger III, 5.6; shank length from outer edge of flexed knee to heel, 10.6; foot length from proximal edge of outer metatarsal tubercle to tip of Toe IV, 9.7; head width between angle of jaws, 7.3; head length diagonally from corner of mouth to tip of snout, 7.2; eye length from posterior to anterior corner, 3.0; eye to naris distance from anterior corner of eye to center of naris, 2.3; distance between centers of nares, 3.2; snout length from anterior corner of eye to tip of snout, 3.8; interorbital distance, 2.2; greatest diameter of tympanum, 1.3.

DESCRIPTION OF TYPE SERIES

MORPHOLOGY: Adult males 21.1–23.4 mm SVL (n = 11, x = 22.16 ± 0.22). Adult females 21.3–23.6 mm SVL (n = 14, x = 22.24 ± 0.22). Ventral surfaces smooth. Dorsal surfaces smooth or weakly granular, with low, conical tubercles scattered over posterior part of body and dorsal surfaces of thighs and shanks. Weak bulge present immediately posterior to rictus.

Head width between angle of jaws 31– 34% of SVL, 0.96–1.11 times head length. Interorbital distance 26–30% of head width. Snout sloped, gently rounded or almost truncate in dorsal aspect, bluntly rounded in profile, protruding beyond jaws (fig. 6). Loreal region flat, vertical or weakly sloped outward to lips. Canthus rostralis sharply rounded, well defined. Eye 40–48% of head length. Eye­naris distance 56–61% of snout length and 61–77% of eye length. Nares directed posteriorly in profile, protuberant in dorsal aspect. Tympanum small; greatest diameter 30–43% of eye length. Teeth on maxillary arch straight, moderately long, not curved and fanglike.

Hand length 20–25% of SVL, 0.89–1.09 times forearm length. Relative lengths of fingers III> I> II ± IV, with Finger II usually longer than IV. Finger IV extended to midpoint between proximal and distal subarticular tubercles of Finger III in most specimens; Finger IV extended to base of distal subarticular tubercle in a few specimens, in which Fingers II and IV are subequal (e.g., MUSM 15607; fig. 9). All fingers free of lateral fringes, with only faint trace of lateral keeling visible under high magnification. Metacarpal fold very weak, forming small, inconspicuous tubercle proximally. One well defined subarticular tubercle on Fingers I, II, and IV; two on Finger III. Palmar tubercle round, low. Thenar tubercle weak, fairly small, slightly elongate. Digital discs weakly expanded. Each finger with pair of prominent dorsal scutes.

Condition of Finger III sexually dimorphic. In adult males, preaxial surface of Finger III with glandular appearance, thicker and ‘‘meatier’’ than other fingers, often with irregular outline in palmar view, enlarged, with subarticular tubercles closer to postaxial than preaxial side of finger (i.e., Finger III of males weakly swollen along entire length). Preaxial surface unexpanded and nonglandular in females.

Shank and foot length 41–47 and 38–46% of SVL, respectively. Relative lengths of appressed toes IV> III> V> II> I (fig. 9). Basal webbing between Toes II–III and III– IV; no webbing between IV–V; preaxial lateral fringe of Toe II well­defined but not expanded into webbing (webbing formula II 1 ½ –3 ½ III 2 ½ –4 IV, following Myers and Duellman, 1982). Weak keels barely discernible on each edge of Toe V, but well­developed fringes present on both edges of all other toes. Weak outer metatarsal fold present, forming weak tubercle proximally in some specimens (e.g., MUSM 17741). Tarsal keel well defined, curved proximally, distally faint but extended to reach inner metatarsal tubercle. Toe discs weakly expanded, each with well­defined dorsal scutes. One subarticular tubercle on Toes I and II, two on III and V, three on IV; all well­defined and protuberant except proximal tubercle on right Toe IV, which is less prominent but always present. Round, protuberant outer metatarsal tubercle and elliptical inner metatarsal tubercle separated by slight bulge.

COLOR IN PRESERVATIVE: The dorsum (fig. 10) is grayish brown. The dorsolateral stripe is stippled gray. In males, the throat is conspicuously solid black, and the chest, most of the belly, and the ventral surface of the upper arm are all stippled gray. Females are ventrally immaculate. Ventral surfaces of legs and groin are free of pigmentation in both sexes. Palmar and plantar surfaces are brown. Contact surfaces of tubercles are gray.

The dorsal thigh color is pale brown, with one dark brown or gray crossband or spot that aligns with a similar band or spot on the dorsal surface of the shank. The anterior surface of the thigh has a diffuse, dark brown stripe from near the knee through the groin and continuous with the dark coloration of the flank. A conspicuous, curved, whitish spot occurs on each side of the cloaca. The shank is dorsally pale brown with a well­defined dark brown transverse band. Concealed surfaces of the thigh (= posterior surfaces of thigh) and shank are dark brown with minute whitish flecks and spots. The preaxial portion of each foot is whitish, free of melanophores. The foot is dorsally brown with one or more dark brown blotches. The posterior surface of the tarsus and plantar surface are dark brown. Contact surfaces of tubercles and digital discs are gray.

The arm is tan or gray with scattered darker spots and blotches. The elbow is conspicuously dark brown. The anterior and posterior surfaces of the upper arm are darker in MUSM 15607, forming dark brown longitudinal stripes.

A broad, blackish brown stripe extends along the flank (fig. 6), through the loreal region, and around the tip of the snout (encompassing the nares). Along the flank, this dark coloration is bordered ventrally by a narrow, moderately defined, white ventrolateral stripe that extends from the groin, above the arm, to the posteroventral border of the eye. Below the ventrolateral stripe, the flank is stippled gray or pale brown, as is the face below the blackish brown face mask. The oblique lateral stripe is present as a diffuse, inconspicuous, pale region or group of small spots extending from the groin to midway along the flank (fig. 6).

NATURAL HISTORY: The four specimens from the type locality were collected in the forest along a trail leading from the Explornapo Lodge to the Amazon Center for Environmental Education and Research (ACEER). Like Colostethus juanii and C. trilineatus , C. melanolaemus occurs near streams but extends at least 25 m into the forest, therefore differing from strictly riparian species confined to the streamside, such as C. abditaurantius and C. imbricolus . Colostethus melanolaemus and C. trilineatus both occur at the type locality of C. melanolaemus near the junction of the Río Napo and the much smaller Río Sucusari .

VOCALIZATIONS

MUSM 15607 (21.5 mm SVL) was recorded for audiospectrographic analysis by Lily O. Rodríguez at 08:00 h from leaf litter at the type locality (AMNH herpetology reel 271). Two uninterrupted sequences of calls were recorded approximately 3–4 m from the frog; temperature data were not taken. The first series includes 14 calls (72 notes) in 27 sec (0.52 calls per sec; 5.14 notes per sec); the second section of tape includes 39 calls (140 notes) in 71 sec (0.28 calls per sec; 1.97 notes per sec). Temporally, calls are highly variable. Each call consists of 1–6 notes (x = 3.6 ± 0.2 notes; mode = 4 notes) separated by intervals of variable duration. Similarly, the time between calls varies from a few to many seconds, with no apparent pattern. Signal interference due to conspecific call overlap obscures many of the temporal parameters in most calls. Nevertheless, examination of isolated calls reveals that the signal is nonpulsatile.

Detailed data were taken from one call composed of four notes (call duration = 751.2 msec), two of five (844.8 msec and 843.7 msec, respectively), and one singlenote call (54.7 msec). As shown in figure 11, emphasized frequencies lie between 3840– 4560 Hz. Notes are weakly frequency modulated from lower to higher. Note duration ranges from 47.3–59.8 msec (n = 15, x = 53.98 ± 1.12 msec). Internote duration ranges from 123.4–236.7 msec (n = 11, x = 153.15 ± 10.76 msec). No pattern of spectral or amplitude modulation within or among calls was discerned.

Throughout the recording, the voucher specimen chorused with another male, heard in the background. Either of the two males initiated calling, but the background male consistently called at a slightly faster rate and emitted longer calls (up to 14 notes per call).

REMARKS

Many species of dendrobatids that are <19 mm SVL lack the distal subarticular tubercle on Finger IV and have Fingers IV ³ II (TG, unpublished data). However, Colostethus melanolaemus is the first species larger than 19 mm that we have seen with this morphology, and it indicates that finger length and number of subarticular tubercles vary independently of body size.

As described above, we coded Finger III as weakly swollen in adult male Colostethus melanolaemus . In some dendrobatids the swelling is conspicuous, either exaggerated distally (e.g., C. nubicola ) or along the entire length of the digit (e.g., C. trilineatus ). In others, including C. melanolaemus , the swelling of Finger III is much more subtle, and in some cases the only way to unambiguously code this character is to compare directly well­prepared, sexually active males and females.

Although the call of Colostethus melanolaemus differs in a number of aspects from that of C. trilineatus , it is nearly indistinguishable from the temporally highly variable call of C. juanii . Insofar as the call of C. juanii has not been described previously, and it bears on the diagnosis of C. melanolaemus , we describe it here. Call data for C. juanii derive from recordings TG 9903 (ICN 44487, 20.8 mm SVL, recorded at 09:45 h, 15 August 1999, air temperature 21.9°C, microphone 60 cm from frog; called from atop a moss­covered boulder immediately adjacent to the stream, overhung by vegetation) and TG 9904 (ICN 44486, 20.3 mm SVL, recorded at 08:20 h, 16 August 1999, air temperature 21.4°C, microphone 25 cm from frog; frog perched on an almost horizontal portion of a moss­covered tree trunk of about 7 cm diameter, approximately 4 m from the stream up a very steep­walled canyon), both made by TG at Villavicencio (type locality; see appendix for details), copied on AMNH herpetology reel 290. Although these two frogs called out in the open, most calling C. juanii were secluded in the leaf litter and other debris from this secondary forest. Calling began at daybreak and abruptly tapered off at around 09:00 h, with only sporadic calling produced infrequently throughout the rest of the daylight hours.

TG 9903 includes two continuous trains of notes separated by a pause of 19 sec. The first continuous train consists of 93 calls (175 notes) in 2.95 min (0.52 calls per sec; 0.99 notes per sec) emitted as single notes, couplets, triplets, and quadruplets; the second train includes 20 calls in 1.17 min (0.28 calls per sec), all produced as single notes. TG 9904 includes one single train of 90 calls (138 notes) in 4.0 min (0.38 calls per sec; 0.58 notes per sec), a second train of 16 calls (32 notes) in 50 sec (0.32 calls per sec; 0.64 notes per sec), and a third train of 63 calls (140 notes) in 3.5 min (0.30 calls per sec; 0.67 notes per sec); the three trains on TG 9904 are all mixtures of single notes, couplets, triplets, and quadruplets. The time between the second and third trains is 63 sec (time between the first and second trains undetermined). Of 284 calls pooled from both recordings, 41.9% are single notes, 35.2% are couplets, 17.6% are triplets, and 5.3% are quadruplets (x = 1.86 ± 0.05 notes per call). No pattern was detected in the sequence of single notes, couplets, triplets, and quadruplets, except that trains begin with a series of single notes. Notes vary continuously from being nonpulsatile to consisting of two or three pronounced pulses.

Detailed analysis was carried out on the first 23 notes of the second train of recording TG 9904 (fig. 12). The first three notes are notably softer than the rest of the train, and they increase in duration (37.5, 46.9, and 62.5 msec, respectively) and emphasized frequency (3560–3720, 3600–3880, and 3720– 4080 Hz, respectively); as such, they appear to be typical ‘‘warm­up’’ calls and are excluded from further analysis. The remaining 20 notes were emitted in 10 calls as two single notes (duration of each 59.4 msec), six couplets (duration 478.1–581.3 msec), one triplet (duration 1093.6 msec), and one quadruplet (duration 1256.2 msec; fig. 12). Signals are frequency modulated from lower to higher, with minimum emphasized frequencies of 3880–4160 Hz and maximum emphasized frequencies of 4120–4560 Hz. Note duration is 53.1–68.8 msec (n = 20, x = 62.03 ± 0.94 msec). Time between calls (groups of notes) is 2–4 sec, and time between notes within a single call (internote duration) is 271.9–468.7 msec (n = 11, x = 389.12 ± 18.89).

Figures

Fig. 6. Lateral view of two similar Amazonian species of Colostethus. Note the variation in the pale area anterior to the groin and the distance of the pale ventrolateral stripe from arm. From top to bottom, C. trilineatus (AMNH FS 8689 Ƌ; MUSM 15618 Ƌ), and C. melanolaemus (AMNH FS 11920 Ƌ; AMNH 114944 ♀). ×2.8.

Fig. 8. A specimen of Colostethus melanolaemus from the type locality. [From color transparency by LOR.]

Fig. 9. Right foot and hand of Colostethus melanolaemus (MUSM 15607). Scale bars = 2 mm.

Fig. 10. Ventral and dorsal views of adult male Colostethus melanolaemus from the type locality. From left to right, top row: AMNH FS 11920, MUSM 17741 (holotype); bottom row: AMNH FS 11922, MUSM 15607. ×2.8.

Fig. 11. Narrow­band (59 Hz) spectrogram and waveform of advertisement call of Colostethus melanolaemus (MUSM 15607).