Bioacoustics of Allobates melanolaemus

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).

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).