Bioacoustics of Hetrodini

Bioacoustics Male tegmina. As in almost all tettigonioids, Hetrodini produce their songs by rubbing the stridulatory file on the lower side of the left tegmen against the scraper, the amplified edge of the right tegmen. In all species studied, left and right tegmen were quite similar in shape ( Fig. 2 ). They do not show structures adapted for sound propagation or amplification like e.g., glossy mirror cells. Species differ in the size of the tegmina and in details of the venation but are in general quite uniform ( Fig. 3 ). Stridulatory files. In all specimens studied by us and by others ( Grzeschik 1969 ) the left tegmen was nearly always placed above the right tegmen as it is typical for tettigonioids. In Eugaster only 4 out of 237 males had a reversed position, but also these males were able to sing ( Grzeschik 1969 ). The left file carried also more and stronger teeth and was longer than that of the right tegmen ( Grzeschik 1969 , Glenn 1991 ). The tooth number in the left file varied between 20 and 65, the length of the file between 1.4 and 4.3 mm , and the intervals between the teeth in the middle of the file between 32 and 136 µm ( Table 1 ; see Fig. 4 for examples). The intervals between the teeth were distinctly larger in the two Acanthoplus species than in all other investigated species. Amplitude pattern. All Hetrodini species studied until now produce non-resonant songs with each syllable consisting of a series of distinct impulses ( Fig. 7 , 8 , 10 ; see also e.g., figures in Kowalski & Lakes-Harlan 2013 ). However, in recordings containing many echoes these impulses can often not be recognised as separated units. According to the grouping of the syllables, the songs can be subdivided into three categories. Some species produce very long (sometimes lasting more than one hour), uninterrupted sequences of syllables (trilling species; Fig. 5A ). Other species have also songs containing series of syllables lasting several seconds, but these sequences and their intervals are typically variable in duration. There is a more or less continuous transition from nearly trill-like sequences ( Fig. 5B 1 ) to short groupings or even single series separated by large gaps ( Fig. 5B 2 , 3 ). The third group of species differs clearly from the preceding ones showing short groups of syllables (echemes) with intervals in a similar range, both quite constant in their duration ( Fig. 5C ). The echemes contained 7 to 31 syllables depending on the species. The syllable repetition rate of the species studied here varied between 7 and 44 Hz ( Table 2 ; all song types ). In all species studied, there seems to be only one type of hemisyllable; the sound is probably produced during the closing movement of the tegmina only. Accordingly, the steep side of the teeth is directed towards the wing edge (in SEM photos of Conti & Viglianisi 2005 ). Opening hemisyllables are missing or are very weak ( Fig. 7I , 8G ). Spectra. The power spectra of the male songs show one broad peak with the maximum always in the high audio range, between 9 and 19 kHz ( Fig. 6 , Table 2 ). The bandwidth 10 dB below peak ranged from 4 to 12 kHz. In interspecific comparisons, there were no obvious correlations between any morphological characteristics (body size, pronotum length, tooth number, file length, inter-tooth intervals) and peak frequency (r 2 =0.01–0.09; p=0.11–0.63) or bandwidth (r 2 =0.00–0.08; p=0.33–0.68; see Table 1 and 2 ). species song type syllable duration syllable period SRR echeme duration syllables per echeme ERR impulses per syllable impulse period ºC peak frequency bandwidth 10dB below peak ms ms Hz s n Hz n ms kHz Acanthoplus discoidalis A 30.0 53.0 19.0 5.5 6.7 26 12.8 Acanthoplus longipes A 43.5 78.0 9.1 7.7 5.8 22 12.8 Cosmoderus femoralis A 14.3 32.2 31.1 14.5 1.1 23 16.4 4.3 Enyaliopsis bloyeti C 32.3 31.0 1.0 30.8 0.6 24 13.7 5.3 Enyaliopsis carolinus B 20.4 44.5 28.9 12.9 19.5 14.8 6.0 Enyaliopsis ephippiatus B 13.8 25.8 39.0 4.4 20.8 0.7 21.3 16.1 10.3 Enyaliopsis sp. 1 (near ephippiatus ) B 45.0 22.3 4.0 23.7 16.0 7.7 Enyaliopsis jennae B 23.0 42.6 23.5 19.4 24.5 11.7 3.6 Enyaliopsis sp. 2 Mpwapwa B 21.7 37.7 26.5 10.0 28.8 0.8 23 12.9 4.9 Enyaliopsis sp. 4 B 24.5 41.0 24.4 2.0 25 10.9 Enyaliopsis nyala C 33.5 29.9 0.2 7.5 1.7 27 Enyaliopsis mulanje C 56.3 17.8 0.7 13 23 Enyaliopsis ilala C 110 9.1 0.77 23 Enyaliopsis nyasa 59.4 16.8 18 Enyaliopsis iaculator C 20.2 41.4 24.2 0.39 13 1.41 24 13.2 Gymnoproctus rammei B 49.0 20.5 7.4 12.7 2.4 8.8 6.4 Gymnoproctus sculpturatus B 25.9 52.9 18.9 6.7 15.3 1.8 20 Gymnoproctus sp. Chenene B 27.5 52.1 19.2 9 13.8 2.1 20 14.7 8.6 Acanthoproctus cervinus C 82 139 7.2 3.08 22 0.07 21 25 10.8 Acanthoproctus diadematus B 99 123 8.1 18.2 175 19 20 10.4 Eugaster guyoni C 16.7 28.0 38.1 0.3 10.4 1.8 1.9 24.2 11.7 6.8 Eugaster spinulosa C 13.4 27.7 37.6 0.4 10.6 1.9 25 16.7 11.8 Eugasteroides loricatus loricatus A 11.8 23.5 43.8 15.6 0.8 19.5 12.2 6.2 Spalacomimus liberianus B 16.0 30.0 33.3 (182) 20.0 25 10.7 Spalacomimus magnus A 16.8 35.3 28.5 16.4 1.3 21 11.6 4.6 Spalacomimus stettinensis C 25.8 40.2 25.6 1.86 47.7 0.285 23.5 10.2 7.8 Spalacomimus talpa A 17.1 45.6 22.1 7.7 43.0 0.5 21.5 12.5 8.9 Spalacomimus verruciferus C 25.1 55.1 18.3 1.1 19.3 0.4 27.3 0.9 21.2 13.7 8.9 Spalacomimus sp. near verruciferus C 19.7 68.9 14.5 2.0 29.0 0.3 19.0 1.1 20 10.8 10.6 Hetrodes pupus A 38.1 62.2 16.1 ? 10.9 Song intensity. The loudness of the song is an important parameter that determines the range of the song to conspecifics and predators, depending also on spectral characteristics of the sounds and of the ears of the receivers. It is rarely measured because the procedure requires special equipment. In Hetrodini, Kowalski & Lakes-Harlan (2010) presented data for one species, and here another three are added ( Table 3 ; all measured or calculated for a singing male in 1 m distance). Our new data may have a tendency for underestimating the loudness because the equipment was not sensitive for ultrasonic frequencies (>20 kHz). The much lower values of Acanthoplus longipes were obtained with equipment sensitive to 10 kHz only according to its datasheet. species dB SPL in 1 m distance n specimen / source Acanthoplus longipes 67 Kowalski & Lakes-Harlan 2010 Eugasteroides loricatus 88 1 Spalacomimus talpa 80 1 Spalacomimus verruciferus 94.5 (94;95) 2 Syntopic occurrences . Despite the large number of (sub)species described there is little information which of these forms do coexist at a certain place and how they might manage to live together. In Table 4 we present all of the surprisingly few examples of syntopic occurrences we could find together with data on body size and song characteristics of the species involved. Locality Species Body size (mm) SRR (Hz) Song type Source 1 NAMIBIA: Rehoboth Acanthoproctus cervinus Acanthoplus discoidalis 45 37 7 19 C A Kowalski & Lakes-Harlan 2013 2 TANZANIA: Lake Chala Eugasteroides loricatus Spalacomimus talpa Spalaco. verruciferus 43 20 34 44 22 18 A A B new data 3 TANZANIA: Lake Jipe, foothills N Pare Eugasteroides loricatus Spalacomimus talpa 43 20 44 22 A A Gerstaecker 1869 4 TANZANIA: Rau Forest Eugasteroides loricatus Spalacomimus talpa Enyal. ephippiatus 43 20 28 44 22 39 A A B new data 5 TANZANIA: East Chenene Spalacomimus magnus Gymnoproctus spec. 48 20 28 19 A B Hemp & Heller 2019 TANZANIA: Puge Simbo Forest Reserve Eugasteroides loricatus Gymnoproctus rammei 43 23 44 20,5 A B Hemp & Heller 2019 6 TANZANIA: Lembeni Enyaliopsis bloyeti Enyal. ephippiatus Spalaco. stettinensis Spalacomimus talpa Spalaco. verruciferus 37 28 29 20 34 31 39 27 22 18 C * B C # A B new data Chromosomes. A comparison of the karyotype of eighteen Hetrodini species/taxa revealed differences in the chromosome number (2n), the chromosome morphology (including X and Y chromosomes), the fundamental number of chromosomes arms (FN), the sex chromosome system, and C-banding pattern (C-band/C-block). The information presented applies to both new and previously published data ( Fig. 13 ; Mbata 2005 , Warchałowska-Śliwa & Bugrov 2009 , Grzywacz et al. 2015 , Warchałowska-Śliwa et al. 2015 ). The examined males had from 29 to 17 chromosomes and one of two sex determination systems: the classical X0 as well as neo-XY. Males of four Hetrodini species belonging to two different subtribes ( Enyaliopsina : Enyaliopsis bloyeti ; Eugastrina : Eugaster —2 species and Eugasteroides loricatus ) have a similar karyotype characterized by 2n = 29 and acrocentric chromosomes including the X chromosome, the largest element in the set. In Hetrodes pupus (Hetrodini) , Enyaliopsis ephippiatus , Enyaliopsis spec. 2 Mpwapwa and Gymnoproctus (both Enyaliopsina ) the complement is reduced to 2n = 27 (all chromosomes acrocentric) as well as in Cosmoderus (Enyaliopsina) and Acanthoplus (Acanthoplina) to 25 with one or two bi-armed pairs of autosomes and an acrocentric or bi-armed X chromosome. The lowest chromosome number, 2n = 17 was found in Spalacomimus magnus (Eugastrina) with five bi-armed autosomes. All the abovementioned taxa show X0 sex determination system. On the other hand, a neo-XY sex chromosome mechanism was also observed in two subtribes: in the genera Enyaliopsis [ E. jennae (2n = 28) and E. carolinus (2n = 26)] and in Spalacomimus [ S. talpa and S. verruciferus (2n = 24) with different morphology of the neo-sex chromosomes]. After C-banding, chromosome regions showed quantitative variation in constitutive heterochromatin blocks among species and genera. For detailed information see Specific part.