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Who is jumping in a Serbian bog? – Orthopteran fauna of the Vlasina region

Vlasina Plateau is a highland bog situated in the mountains of southeastern Serbia, close to the border with Bulgaria. From a conservation point of view, bogs are one of the most important habitats and they are considered as threatened all across Europe. As the Orthopteran fauna of southern European bogs has not been studied in detail, we decided to make an inventory of grasshoppers and bush-crickets of Vlasina region. During eight years (2012 to 2019) of orthopterological study, 63 species were recorded at Vlasina Plateau. Interesting findings are those of Balkan Field Grasshopper (Chorthippus bornhalmi) and Bures’ Bush-cricket (Isophya bureschi) recently reported as first for Serbia, as well as regionally rare Serbian Pygmy Bush-cricket (Anterastes serbicus), Domogled Meadow Bush-cricket (Broughtonia domogledi), Short-winged Cone-head (Conocephalus dorsalis), Club-legged Grasshopper ( Gomphocerus sibiricus), Fieber’s Walking Bush-cricket (Psorodonotus fieberi) and Pygmy Toothed Grasshopper (Stenobothrus crassipes). In addition, we provided new distributional and bioacoustic data for Poecilimon pseudornatus and I. bureschi.


Introduction
Peatlands are peculiar wet habitats rich in accumulated dead organic matter. They are characteristic for areas that meet several combined climatic and pedological features, such as high soil humidity with low nutrients as well as low annual and minimal temperature, and they usually appear across the Northern Hemisphere, the most numerous being those in taiga and tundra (Langheinrich et al. 2004). Despite their long-time recognized status of high conservation significance, due to ongoing climate change, increasing habitat degradation caused by human activities, and succession (Brigić et al. 2019), peatlands are still among the most vulnerable and endangered sites (Langheinrich et al. 2004). Well-studied peatlands in the Western Balkans are bogs, i.e. peatlands rich in Sphagnum (see e.g. Brigić et al. 2017), which are today small and disjunctive remnants of Pleistocene meadows exhibiting boreal fauna and flora (Horvat 1950;Topić and Stančić 2006). There are several peat bogs in Serbia, mainly in the southwestern and southeastern part of the country, some of them among the largest in the Balkans. Examples are the Pešter Plateau and Vlasina Plateau (Šovran et al. 2013). Vlasinsko blato (Vlasina mud) in southeastern Serbia was considered to be the largest peat bog in Balkan Peninsula prior to its submersion in the 1950s. Although most of its parts were submerged, crucial habitats with endemic and relict species survived, and amongst these species, the best known is the insectivorous Drosera rotundifolia L. (Ranđelović and Zlatković 2010). Today, the remaining peatland is conserved under the "Vlasina" Landscape of Outstanding Features. In this area, intensive research has been carried on numerous taxa, mostly vertebrates -birds (Puzović et al. 2009), reptiles and amphibians (Crnobrnja-Isailović et al. 2011;Dinov and Crnobrnja-Isailović 2013); but also some invertebrates -ants (Petrov 2011), butterflies (Tot et al. 2015;Tot et al. 2017), true bugs (Šeat 2017), hoverflies (Tot et al. 2018) and dragonflies (Đukić et al. 2019).
Literature data on Orthoptera of the Vlasina region are scarce (Pančić 1883;Adamović 1950Adamović , 1975Skejo and Ivković 2015;Pavićević et al. 2014), so we aim to gather all historic data as well as new information related to the group in this peculiar peatland. We briefly present composition of the grasshoppers' assemblages at each locality, provide new data about song and distribution of Poecilimon pseudornatus and Isophya bureschi in Serbia and we put the highland into context of European Orthoptera fauna.

Material and methods
Studied area. Vlasina Plateau, situated in SE Serbia (Fig. 1), close to the border with Bulgaria, represents a mountainous peatbog in the centre of the Balkan Peninsula. Average height of area is from 1000 to 1300 m a.s.l. In the centre of plateau there is Vlasina Lake, laying at 1210 m a.s.l. The lake is surrounded by the numerous peaks -Čemernik Mt. (1638 m a.s.l.) to the west, Gramada Mt. (1721 m a.s.l.) to  (Figs 2A, B, C), whereas forest vegetation is reduced to small fragments as a consequence of anthropogenic activities in the past (Ranđelović and Zlatković 2010). Data collection. Orthoptera were investigated in the field on 151 localities between 2012 and 2019 ( Fig. 1) by common entomological methods (visual and acoustic searching, sweep netting). All the species were identified to species level and usually photographed or collected for evidence. Part of collected material was pinned, while the majority was preserved in 96% ethanol. Besides fieldwork investigations, amateur data on Orthoptera of Vlasina were collected from Serbian web pages specialized in biodiversity data accumulation and curation -Alciphron (Ivković 2014(Ivković -2020 and Biologer (Popović et al. 2020). All detailed data are provided in Supplementary file 1.
Bioacoustic terminology. Audio recordings were taken with a Roland R-05 digital audio recorder (sampling rate 96 kHz, 24-bit amplitude resolution, microphone response frequency up to 40 kHz). Sound analysis and figures of the oscillo- grams were prepared using Adobe Audio CC 2015 software. The song terminology follows Heller et al. (2004): calling song -song produced by an isolated male; functional unit of the song -the smallest part of the song, which contains all necessary song elements in appropriate order to elicit a female response; syllable -the sound produced by one complete up (opening) and down (closing) stroke of the forewings; impulse -a simple, undivided, transient train of sound waves; after-click -click produced with considerable delay after the main impulse group. Identification and taxonomy. Specimens were determined using Harz (1969Harz ( , 1975, Iorgu & Iorgu (2008), Willemse (1985)

Results
Based on published data and results presented in this article, a total of 64 orthopteran species occur in the area of Vlasina lake. Of these, 30 belong to Ensifera and 34 to Caelifera. Four species -Oedipoda caerulescens (Linnaeus, 1758), reported by Adamović (1950), Oedaleus decorus (Germar, 1825), Chorthippus mollis ( Charpentier, 1825) reported by Adamović (1975) and Poecilimon schmidtii (Fieber, 1853) (leg. M. Karaman, 17.7.1971), deposited in the Zoological Collection of the Department of Biology and Ecology at Novi Sad (ZZDBE), were not recorded during our surveys and they are thus not included in the list of species. We can expect that these species are still present in the area of Vlasina Lake, but during our field trips, we probably overlooked them.

Notes on interesting species
Isophya bureschi (Fig. 3A) -Until recently, this species was known in Serbia only from the Vlasina Plateau. Here, we report one new locality situated in Senokos, eastern Serbia (N 43.15901°, E 22.93186°). Stridulatory file in male from Senokos bears 72 teeth (Fig. 3B) and in two males from Vlasina Lake 66 and 71 teeth, while in both populations males have a long and pointed cercal tooth (Figs 3C-E). According to our observations, the song of I. bureschi can be heard from a distance   Fig. 4A) in central and eastern Serbia, we discovered that P. pseudornatus has a wider distribution range, whereas the locality around Vlasina Lake represented the easternmost finding of   2,3,9,28,29,32,35,38,40,45,55,59,62,65,67,74,81,87,91,99,100,101,105,109,111,119,124,140 Isophya speciosa (Frivaldszky, 1868)  13,21,25,26,27,29,31,35,37,40,59,64,69,75,76,77,78,79,82,84,87,90,98,99,102,103,107,111,112,113,119,121,135,142,147 Pseudopodisma fieberi (Scudder, 1897) this species. New distribution data raised the question about the distribution of P. pseudornatus and P. affinis in Serbia (Fig. 5), a topic already discussed by Chobanov and Heller (2010). The main problems in this matter are the lack of research in Serbia and the fact that the previous authors used only the morphological details, whereas they did not use the song, which is the most significant character for distinguishing between the species from the P. ornatus group. Based on the analysed specimens, we can confirm that P. ornatus is not present in Serbia; thus, it has been confused with either P. pseudornatus or P. affinis.

Discussion
Orthopteran fauna of the alpine habitats of Serbia remains poorly studied; Grebenščikov (1950) provided data on orthoptera found on high mountains, but as his research data was obtained from several mountains in Serbia, it is not comparable with research presented in this article. To date, only Adamović and Mladenović (1993-94) provided information on the orthopteran fauna on peat bogs in Serbia to date, and they reported 23 species, most of which were found at Vlasina Plateau. Only two species reported by Adamović and Mladenović -Polysarcus scutatus (Brunner von Wattenwyl, 1882) and Broughtonia arnoldi (Ramme, 1933), were not reported from Vlasina Plateau. The majority of the investigated species are endangered by habitat loss caused by the rapid tourism development in the area around Vlasina Lake. One of the endangered species is Broughtonia domogledi, whose populations are threatened with habitat destruction throughout their distribution range (Chobanov et al. 2016). We observed this species around Vlasina Lake in a tourist resort. Even though the species is very common on Vlasina Plateau in late summer, the conservation of its habitats is still necessary. Besides habitat loss, the greatest threat not only to Orthoptera, but to the entire flora and fauna of Vlasina Plateau, are small hydropower plants constructed on several rivers in Crna Trava municipality. Regardless of the fact that Vlasina Lake is man-made, extensive changes, such as water regime changes, can