Bioacoustics of Mecopoda stridulata

Remarks. From the dimensions of the stridulatory organs the species belongs to the Mecopoda subgroup niponensis . It differs in song clearly from all other species of the subgroup and also from M. yunnana by producing very short song units (single syllables), separated by short silent gaps from the preceding and following syllables ( Figs. 6–7 ). Concerning the inter-tooth distances, the file is relatively homogenous ( Figs. 11 F , 12 ) like that of M. fallax and M. yunnana [using fig. 5l ( M. minor ) in Liu et al. 2020 for comparison instead of the smaller fig. 5m ( M. yunnana ) following the description of the sizes in the text]. The distances start anally at around 40–50 µm, do not exceed about 70 µm in the middle of the file and become smaller than 40 µm only near to the articulation ( Fig. 12 ). In song, M. s. stridulata differs clearly from M. fallax , but its SRR is quite similar to the rhythm in the trill phase of M. yunnana . M. yunnana , however, seems to produce fast syllable groups (Liu Cx et al. 2020). Further bioacoustic and genetic studies have to confirm that M. s. stridulata really belongs to the niponensis subgroup.

Other specimens studied. All MALAYSIA , Sabah (Borneo): 1 male (3261450), Kota Kinabalu, 9.viii.1984 , (secondary vegetation) , CI [additional label “Stridulation = gleichmässiges Zwitschern” (stridulation=uniform chirping)]. 3 males , OTRmeceloS15-17 ( ZFMK ), Matunggong , 19 viii 1992 , coll. K. Riede. Our specimens were identified on base of male 3261450 which has a file in structure nearly identical to that of the holotype of Mecopoda stridulata stridulata . The song of this specimen was described as ‚uniformly chirping‘ fitting well to the recordings mentioned above. The specimens with this song, however, differ slightly in file structure. Song. The long lasting calling song (recording of M2 lasting 136 s, of M3 89 s) consists of single isolated syllables, produced with an SRR of 8.3 Hz ( Figs. 6–7 ; T = 20ºC). Within the syllable, a short (10 ms) and soft part is followed by a much louder and longer (20 ms) part. This second part had a resonant structure with the strongest component sweeping upwards from 7.3 to 8.3 kHz. The fundamental at 2.5 kHz was clearly visible, but the second strongest harmonic was at 10 kHz. Additional description. Morphologically the Bornean species differs from M. himalaya by the following, although weak, morphological characters: the pair of teeth at the end of the male cercus are of nearly identical size and are clearly spaced from each other instead of having the apical tooth markedly larger than the preapical tooth and both teeth inserted rather close to each other. Further on, the styli at tip of the male subgenital plate are thin and short but less shortened than in the latter species. Male cerci not very stout at base, narrow apical area little curved mediad and provided at end with two small acute teeth of rather equal size that are markedly spaced from each other ( Fig. 3 L–O ). Stridulatory file long (5.0– 5.8 mm ), with about 106–126 teeth. Subgenital plate moderately wide, narrowed from base towards midlength; divided into two lobes in apical area; apical incision about 0.26–0.28 times the length of the subgenital plate; styli short and thin. There are brown and green color variants.