Bioacoustics of Dinarippiger discoidalis

Our study establishes the basis for future research on the genus Dinarippiger gen . nov . by presenting a comprehensive overview of the D. discoidalis comb . nov . occurrence in the Dinaric Alps. Special attention was given to the syntopic occurrence of D. discoidalis comb. nov. and Ephippiger species. At the present moment, we know that in several localities in Slovenia , Croatia , and Bosnia & Herzegovina the species co-occurs with E. ephippiger , a central European and Balkan species. In another part of its distribution, i.e., in Istria and Primorska region of Slovenia , D. discoidalis comb . nov . occurs syntopically either with another species of the genus Ephippiger , Alpine E. persicarius , or with a hybrid population of E. ephippiger x E. persicarius . This could be an interesting biogeographical case that requires further attention, as E. ephippiger and E. persicarius could be two subspecies of a single species, which would provide further confirmation that Ephippiger is an Apennine genus whose representatives spread to Eastern Europe relatively recently across the Western Balkans or along the northern banks of the Sava River. The area between Slovenia and Croatia is a well-known glacial micro-refugium ( Taberlet et al. 1998 , Joger et al. 2007 , Jablonski et al. 2017 , Wang et al. 2022 ) due to its contact with the Alps, the Dinaric Alps, the Pannonian basin, the Adriatic coast, and the Po region, harbouring ice-free habitats during the last glaciation. In many groups of plants and animals, these areas represent either the center of dispersal or the secondary contact regions ( Surget-Groba et al. 2002 , Brus 2010 , Dufresnes et al. 2020 , García et al. 2020 ). Dinarippiger discoidalis comb . nov . does not hybridize with any of the Ephippiger species in the areas of sympatric occurrence. Another interesting biogeographical and phylogenetic question is the presence of a single, highly variable species within the newly established Dinarippiger gen . nov . or several distinct species with more restricted distributions and currently undefined diagnostic traits. Many authors have tried to assess the intraspecific variability of D. discoidalis comb . nov . , but have failed in reaching a definite conclusion (e.g., Fieber 1854, Krauss 1879 ). Previous authors have focused mostly on body size ( Fieber 1853 , Krauss 187), the number of inner and outer spines on the hind tibiae ( Werner 1920 ), or calling song traits ( Gomboc & Šegula 2014 ). Werner (1920) did not manage to find any consistent differences among D. discoidalis comb . nov . populations and noted that the substantial overlaps in trait variability could be the evidence of a single highly variable species. However, in the same study, Werner (1920) noted the presence of a northern smaller race and a southern larger race, but apart from body size no clear differences between the two were found. Geographical variation in body size is, for example, present in Italian Ephippiger cavannai Targioni Tozzetti, 1881 , a species characterized by smaller individuals in montane locations and larger ones in the coastal areas ( Massa et al. , 2012 ). Galvagni (1956) initially described a separate taxon, E. perforatus tamaninii , which later turned out to be a montane population of E. cavannai . Without a systematic comparison of the individuals from distant and isolated populations, variability within D. discoidalis comb . nov . remains an open question. This issue is illustrated by a photograph of a peculiar male ( Fig. 13 ) from Vremščica Mt. ( Slovenia ), serving as a reminder that future studies have to include a phylogeographical survey, detailed morphometric analyses, as well as comparative morphological and bioacoustic approach.

The song of Dinarippiger discoidalis comb. nov. was first described by Harz (1967) and later analyzed and visualized by several other scientists ( Keuper et al. 1988 a , 1988b, Heller 1988 , Keuper 1989 , Jatho et al. 1992 , Jatho 1995 , Massa et al. 2012 ). Our data corroborate the findings of the previous studies, showing that the song consists of echemes containing 3–7 (only very rarely 1–2) syllables ( Fig. 11A–D ). In structure, it is thus similar to the songs of Ephippiger species (see Jatho et al. 1992 , Massa et al. 2012 ) but differs clearly from the songs of the European Uromenus species ( Heller et al. 2021 ). Each syllable has a distinct opening and closing hemisyllable made by a series of strongly dampened impulses. These short elements are produced by jumping of the scraper against the teeth of the stridulatory file (see Fig. 11D ) as is typical for Ephippigerini . The frequency spectrum of the song has its peak in the ultrasound, around 20 to 40 kHz ( Fig. 11E ; Keuper et al. 1988b ). A relatively high syllable number per echeme should enable D. discoidalis comb. nov . females to discriminate against the mono- or disyllabic song of E. ephippiger when the species co-occur in the same habitat in Slovenia (see above), Croatia (see above), Bosnia & Herzegovina (Mikšić 1969) or Montenegro ( Ingrisch & Pavićević 2012 ). In the Ephippiger diurnus complex, syllable number per echeme is important for phonotactic female choice ( Ritchie 1991 ). However, after a closer inspection of the temporal parameters of amplitude modulation (besides syllable number per echeme), an unexpectedly large variation has been observed ( Table 1 ), even when taking the effects of temperature into account. Our data are too limited for drawing conclusions but among-individual differences as large as the ones found within a single field recording ( Gomboc & Šegula 2014 ; #61) are quite surprising, despite the fact that animals in the sun may sing much faster than the ones in the shade. Locality T NSE EP DOH DCH DS SP SRR NI IP TN Source Italy (Trieste) 23 5 6.4 (n=9) 30 94 128 148 6.8 47 3.1 - Massa et al . 2012 . #2 Slovenia (Istria) 24 6 11.2 (n=3) 59 434 514 543 1.8 81 5.8 - Gomboc & Šegula 2014 . # 60 Slovenia (Vremščica) 24 4–6 4.3 (n=8) 46 143 199 237 4.2 43 5.3 - Gomboc & Šegula 2014 . # 61 Croatia (M. Učka) ? 4–5 3.9 (n=10) 36 105 149 185 5.4 43 3.1 - Massa et al . 2012 #1 Croatia (Rijeka) ? 3–7 1–1.5 - - - - - - - - Harz 1967 Croatia (Rijeka) 25±2 3–7 - 23.6 92.2 125.7 149.6 6.7 39.5 - 83±6 Keuper et al . 1988, Jatho et al . 1993, Jatho 1995 Croatia (Rijeka) 20 4 - 32.5 183.5 229.5 245 4.1 63.5 3.85 - this paper Croatia (Rijeka) 24.5 4 - 51.5 342.5 408.5 435.5 2.3 65 6.4 - this paper Croatia (Rijeka) 23 3 - 53 235 306 335 3.0 - - - this paper Croatia (Pag) ? 2–4(5) 1–1.5 - - - - - - - Duijm 1990 Croatia (Žuljana) 25 (1)4 - 25 239 284 312 3.2 43 5.7 - this paper Croatia (Hvar Isl.) 35 5–6 12.8 (n=4) 30 179 227 251 4.0 68 2.9 - this paper Montenegro (Kotor) >28 4–7 4.2 (n=10) 18 73 99 116.5 8.6 32.5 2.9 113 this paper, Heller 1988 Montenegro (Golije Mt.) 26 2–3 3.5 (n=6) 22 203 238 260 3.8 - - - this paper The stridulatory structures are situated on the tegmina of both males and females. In the males, the stridulatory file is located on the underside of the left tegmen, whereas in the females it is situated diagonally on the upper side of the right tegmen ( Fig. 12A–D ). Correspondingly, the scraper is formed by the inner edge of the right tegmen in the male and of the left tegmen in the female. The right tegmen of the male carries a large glossy mirror cell. Stridulatory teeth are rather symmetrical ( Fig. 12E–F ) as can be expected for a species with loud opening and closing hemisyllables. In the female, the stridulatory structures may be used exclusively in a defensive context, a function already mentioned by Krauss (1878) for this species. Judging from the very limited data on the number of teeth in the male stridulatory file, differences among populations may exist (see Table 1 ).