Bioacoustics of Hyloxalus alessandroi

REMARKS Given the overall morphological similarity and geographic distributions of Colostethus alessandroi and C. mcdiarmidi , it is likely that they are closely related. Indeed, the possibility exists that they are geographic variants of a single species, such as extremes in a cline. However, although few specimens are presently available, we compared directly equivalent semaphoronts (adult males) from several localities and found no evidence of clinal variation along either a latitudinal or altitudinal gradient, 7 and a number of characters distinguish the two groups. Additional specimens, especially from intermediate localities, are required to further assess intraspecific variation and test our hypothesis. Similarly, the inclusion of additional lines of evidence (e.g., vocalizations, osteology, DNA sequence data) could further elucidate this problem, although failure to discover differences in them would not necessarily prove these populations to be conspecific.

NATURAL HISTORY: Colostethus alessandroi is riparian. All the specimens collected to date were taken from habitats in early stages of succession. Males were observed calling beside streams, perched on moss­covered rocks or fallen vegetation, or hidden among rocks and vegetation. Calling activity was greatest in early morning and tapered off by midday, although it also was observed to continue into the afternoon, especially during the rainy season. VOCALIZATIONS An uncollected individual was recorded by Alessandro Catenazzi at a creek at the type locality at 10:00 h on 21 February 1999 , 17.4°C (AMNH herpetology reel 289). Although the specimen evaded capture, it was clearly observed calling from a moss­covered rock overhung by tree roots; many other specimens were also observed calling, and all emitted the same vocalization. Data were taken from a continuous train of 321 couplets and two single notes in 1.40 min of continuous tape. Couplets are produced rhythmically at an average rate of 1.58 couplets per sec. Detailed data were taken from the first 35 vocalizations of this series; the two single notes were pooled with the first notes of couplets. The duration of the first note of each couplet is significantly longer than the second note ( P = 0.0001); the first note ranges from 84.4–103.1 msec ( n = 35, x = 91.96 ± 0.62 msec), whereas the second note is 75.0–87.5 msec ( n = 33, x = 81.06 ± 0.64 msec). Internote duration is 34.4–53.1 msec ( n = 33, x = 46.69 ± 0.65 msec). Time between couplets is 212.5–596.9 msec ( n = 33, x = 365.4 ± 19.6 msec). Notes are weakly or nonpulsatile. Spectral energy is concentrated between 3400–4320 Hz with the greatest energy peak at 3720–4160 Hz ( n = 68, x = 3881 ± 10 Hz); all but four of the 35 calls exhibit greatest energy peaks below 4.0 kHz. Each note is strongly frequency modulated from lower to higher (fig. 18). The two notes of each couplet overlap almost completely in all spectral parameters and are only statistically distinguishable in that the minimum frequency of the first note is slightly higher than the second note (first note: n = 35, x = 3512 ± 9 Hz; second note: n = 33, x = 3484 ± 9 Hz; P = 0.0351).