Bioacoustics of Mecopoda niponensis

The species can morphologically be separated from all other congeneric species by its short and wide tegmina ( Fig. 5 A ; see measurements in Liu Cx et al. 2020). Also its trilling calling song, studied in China (Liu YF et al. 2019; Liu Cx et al. 2020), Japan ( Ichikawa et al. 2006 ; Yamamoto 2006) and Korea ( Kim 2009 ), shows a characteristic amplitude modulation (see Fig. 6–7 ), clearly different from other Mecopoda species. However, we have a specimen from Vietnam at hand in which morphology and song pattern disagree. The trilling song of this animal shows the typical niponensis pattern, but it has unusually long and narrow tegmina. With a length/width ratio of 3.43 it is just outside the range (2.19–3.36) given by Liu Cx et al. (2020) for niponensis . More important, the tegmen length ( 55 mm ) is far outside the range of niponensis ( 34–49 mm , Liu Cx et al. 2020; 40–43 mm in Korea , Storozhenko et al. 2015 ). Since it has additional song components not known from niponensis , and was found outside the known range of the species, we consider it as member of a new subspecies (see below).

Diagnosis. Differs from the nominate subspecies by longer tegmina, from other Mecopoda species by the characteristic amplitude modulation in the trill (see Fig. 6–7 ) and from the Vietnamese species M. ampla and M. prominens in file structure (see Fig. 11–12 ). Morphology. As nominate subspecies, but with longer tegmina (see above). Song. The recorded specimen had an unusually variable song containing two elements. It produced trill-like series, quite similar to the song of the continental subspecies ( Fig. 6 ) and to that known from other parts of its range (for details see Liu Cx et al. 2020). These series last for many minutes and have a relatively complicated structure. Within a song unit, the low-amplitude beginning and ending phases consist of repeated simple syllables, while the high-amplitude climax is composed of many repeated subunits. In the recorded specimen the subunits consisted of five to six syllables with a characteristic amplitude pattern ( Fig. 7 ). In other parts of its range like Japan and Korea ( n. niponensis ) one subunit seems to have typically only three syllables ( Ichikawa et al. 2006 ; Kim 2009 ). Besides the trills, the specimen produced also occasionally long series of echemes before the trill. In the frequency spectrum, the ultrasound components were even stronger than the peak in the audible range ( Fig. 14 ). Stridulatory file. Like specimens of the nominate subspecies, also the Vietnamese specimen has a long file carrying about 115 teeth ( Fig. 11 B ) like M. n. niponenis . The inter-teeth distances start anally with 50 µm and reach their maximum of about 80 µm between the 30th and 40th tooth ( Fig. 12 ). In the file of the lectotype of M. n. niponenis the inter-tooth distances are slightly smaller but there is some variability in this character. The file of the M. n. continentalis specimen (105 teeth) photographed by Liu Cx et al. (2020) is similar to M. n. vietnamica n. ssp, but has the maximum around the 50th tooth. Another Chinese specimen of M. n. continentalis ( Fig. 11 A ; CH 7674, 107 teeth) is between the lastly mentioned and M. n. vietnamica subsp. nov. , and the specimen from Fujian ( M. n. continentalis ; 115 teeth) is similar to the lectotype of M. n. niponenis ( Fig. 12 ).