Bioacoustics of Nisitrus malaya

Diagnosis Average size, colouration contrasting with black and yellow, characterised by black vertex, yellow frons and orange brown legs. This new species is very close to N. vittatus from which it differs by adult and juvenile colouration, male and female genitalia and calling song. General colouration darker, particularly among FW cells and veins beneath R; R black (instead of cream-coloured as in N. vittatus ); in male venation, anal-most and middle chords narrow and nearly parallel with one another (instead of diverging apically), and basal-most chord extend from basal half of middle chord (instead of at/after midpoint). It differs from N. vittatus by the male genitalia with pseudepiphallus more robust, broad, anterior margin more strongly concave. Female copulatory papilla with truncated lobule at the ventro-anterior end. Juvenile differs strikingly in the body colour pattern. Male calling song also differs by longer echeme period. This species is also similar to N. crucius sp. nov. in size and habitus, but differs by the absence of cross-shaped black pattern on frons and does not occur in Borneo.

Calling song ( Singapore , n = 4 males , 20 echemes; MNHN-SO-2851–2854) ( Fig. 25A–C ) At 27.3°C, the calling song consists of bouts of highly variable length, ranging from a few seconds to several minutes. Each bout is composed of short echemes made of triplets of syllables; echeme duration is 32.3 ± 2.8 ms (29.0–37.56 ms); echeme period is 64.5± 4.3 ms (59.5–75.5 ms); downtime between consecutive echemes is 32.1 ±4.4 ms (24.3–41.3 ms). Durations for the first to third syllables of the triplet are as follows: 6.1 ±1.5 ms (3.7–8.0 ms), 6.7 ± 2.7 ms (2.5–10.6 ms) and 5.8± 2.9 ms (3.0–11.2 ms). Call spectrum consists of a series of harmonics with three distinct peaks in the first three harmonics: first harmonic (fundamental frequency) at 7.35± 1.28 kHz (6.201–9.39 kHz), which is also the dominant frequency; second harmonic at 13.33± 1.01 kHz (12.23–15.07 kHz); third harmonic at 18.88 ±0.77 kHz (17.23–20.07 kHz).

Remarks We split the species previously recognised as N. vittatus into two distinct species after integrating evidence from general and nymphal colouration, female genitalia morphology, acoustics, DNA (12S sequence) and distribution. In terms of adult morphology, the new species is very similar to N. vittatus in habitus, other than being darker in colouration. The male genitalia are not always distinguishable between these species; but the sclerotization of the female genitalia can be differentiated. However, the colour patterns in the nymphs are drastically different. Likewise, a multivariate analysis of the call properties also showed distinct calling songs. The 12S gene tree also demonstrates that the two species form distinct clades. Lastly, the new species occurs in Malay Peninsula whereas N. vittatus occurs in Borneo and Sumatra . Integrating these pieces of evidence indicates that N. vittatus and N. malaya sp. nov. are indeed separate species having probably diverged recently, despite the similarities in adult habitus and male genitalia.