Unusual call characteristics and acoustic niche adaptation of Limnonectes larvaepartus Iskandar, Evans & Mcguire, 2014 in its habitat (Anura: Dicroglossidae)

Abstract

The advertisement call of Limnonectes larvaepartus is unique among frogs of the genus Limnonectes which have a true acoustic organ. The calls of three adult males L. larvaepartus were recorded at the foothill of Hutadelita Mountain (N 000 48’ 48.3” E 1220 23’ 00.8”; 396 m asl), Nantu Wildlife Sanctuary, Gorontalo, northern Sulawesi by using an Olympus LS-11 recorder with built-in microphones. Air temperature during recording was around 26°C. Adobe Audition 3.0 software was used to visualize and analyze the calls. The advertisement calls consist of 1-6 pulses, though only one pulse is usually produced. The wave structure of the call of L. laervaepartus is unusual because it is characterized by a short series of pulses that form a pulse train. Each pulse from the beginning of the call until the middle of the call has its own frequency spectrum, whereas the pulse train during the second half of the call becomes tightly compressed and forms one frequency spectrum. Calls of L. larvaepartus do not have a dominant frequency. Minimum frequencies decrease gradually from the beginning to the end of the pulse train; however, the maximum frequency rises gradually. Ascending frequency characters in one pulse also occur in the energy spectrum and bandwidth of frequency. The lowest minimum frequency at the end of pulse train is ~165 Hz; while the highest maximum frequency is also located at the end of the pulse train and is ~6860 Hz. The short pulses call of L. larvaepertus is similar to that of L. hasceanus, although the two species are not close relatives; in L. larvaepartus, the pulse only consists of one period, whereas in L. haschenus it consists of two periods. Considering acoustic adaptation, call of L. larvaepartus has similar frequency spectrum with call of L. modestus, we assume that they would not call at the same time and at the same localities because of their similar acoustic niches.