Diversity and distribution of the millipedes (Diplopoda) of Georgia, Caucasus

Abstract The diplopod fauna of Georgia, Transcaucasia, is very rich given the country’s relatively small territory; it presently comprises 103 species from 44 genera, 12 families, and 7 orders. Most of the Diplopoda known from Georgia (86 species, or 83%) demonstrate Caucasian distribution patterns, 36 and 46 species, as well as 8 and 9 genera being endemic or subendemic to the country, respectively. A single Holarctic family, Anthroleucosomatidae (order Chordeumatida), contains 44 Caucasian species and 20 genera, of which 27 species and 14 genera are endemic or subendemic to Georgia. Likewise, all species from the orders Polyzoniida, Siphonocryptida, Glomerida and Chordeumatida, as well as most species of Julida and Polydesmida are native, also endemic or subendemic to the Caucasus, but the genera and families they represent are widely distributed at least across the Euro-Mediterranean Realm. Most of the presumed troglobionts in the Caucasus appear to be confined to western Georgia’s karst caves (14 species, 5 genera). Within Georgia, the fauna of the western part (= Colchis) is particularly rich and diverse, while that of the central and eastern parts of the country grows increasingly depauperate inland following the gradual climatic aridisation from west (Black Sea coast) to east (Armenia and Azerbaijan). The vertical distribution of the Diplopoda in Georgia, as well as the Caucasus generally, shows the bulk of the fauna restricted to forested lowland to mountain biomes or their remnants. Only very few Chordeumatida and Julus species seem to occur solely in the subalpine to alpine environments and thus may provisionally be considered as high-montane elements. Ongoing and future research on the millipedes of the Caucasus, especially in cave and montane environments, will undoubtedly allow for many more novelties and details of the diversity and distribution of Georgia’s Diplopoda to be revealed or refined.


Introduction
Georgia is one of the main countries in the Caucasus, lying between western Asia and Eastern Europe. It is bounded in the west by the Black Sea, in the north by Russia, in the south by Turkey, and in the southeast and east by Armenia and Azerbaijan (Fig. 1). The area is mainly montane to high montane, situated between 41° and 44°N, and 40° and 47°E. The Greater Caucasus Mountain Range, or Caucasus Major, forms the northern border of Georgia, while the southern border is bounded by the Lesser Caucasus Mountains, or Caucasus Minor. The Caucasus Major is much higher in elevation (more than 5000 m a.s.l.) than the plateau-like Caucasus Minor, both being connected by the submeridional Surami (= Likhi) Mountain Range which divides Georgia into the western and central + eastern parts. Both parts are quite varied in climate and biota. Western Georgia's landscape ranges from lowland marsh-forests, swamps, and temperate rainforests within the Colchis Plain to eternal snows and glaciers, while the eastern part of the country even contains a small segment of semi-arid plains. Forests cover around 40% of Georgia's territory, while the alpine/subalpine zone accounts for approximately 10% of the land. The climate of Georgia is extremely diverse, considering the nation's small size, but is largely mild to warm. There are two main climatic zones, roughly corresponding to the eastern and western parts of the country. The Greater Caucasus Mountain Range plays an important role in moderating Georgia's climate and protects the nation from the penetration of colder air masses from the north. The Lesser Caucasus Mountains partially protect the region from the influence of dry and hot air masses from the south (Bondyrev et al. 2015).
The millipede fauna of Georgia has recently been reviewed and shown to comprise 95 species from 42 genera, 12 families, and 7 orders (Kokhia and Golovatch 2018). A few relevant faunistic papers have, or will have, appeared since (Golovatch 2018, Golovatch and Turbanov 2017, Antić et al. 2018, Evsyukov et al. 2018, 2020, Vagalinski and Lazányi 2018, Short et al. 2020, allowing for the previous checklist to be rectified and updated, as well as the previous reference list to be considerably shortened. The present checklist contains 103 species from 44 genera, 12 families, and 7 orders (Table 1). Data on the elevations at which the species occur, both within and beyond Georgia, are also added, representing the basic information for our analysis of millipede vertical distributions.

Material and methods
Only described species and published records are considered in our paper, while dubious taxa and those not identified to the species level have been omitted both from the checklist and reference list. Only one important exception has been made: Calyptophyllum sp. as the only record of this genus in the Caucasus (Table 1). Three zigzag transects chosen to grossly reflect the north-to-south lie of the macro relief of Georgia, extending from the Caucasus Major in the north to the Caucasus Minor in the south (Figs 2-5), have been drawn, one each for the western, central and eastern parts of the country (Fig. 1). The transect across western Georgia connects Pitsunda -Arabika Plateau -Khaishi -Bagdati -Batumi (427 km long), that in central Georgia connects Roki Tunnel -Tskhinvali -Tbilisi -Tsalka Reservoir -Ninotsminda -Javakheti National Park (275 km), and the eastern Georgia one connects Omalo -Tianeti -Akhmeta -Shilda -Kvareli -Lagodekhi -Tamariani (186 km) (Fig. 2). Both at the bottom of the maps and on the maps themselves, each transect is accompanied by the respective altitudes given for each of the turn localities and thus provides a clear generalized picture of the macro relief (Figs 3-5). These three transects thus cover all major variations in millipede vertical distribution across entire Georgia. This novel approach to a graphic presentation of faunistic results allows us to combine the horizontal and vertical distributions of millipedes in the easiest and most vivid way on the same map. Mapping largely concerns endemic or subendemic species and concerns only the territory of Georgia.
Most of the colour maps were generated using Google Earth Pro version 7.3.2.5495 and Adobe Photoshop CS6. The final images were processed with Adobe Photoshop CS6.

Main relevant references
Family Glomeridellidae Genus Typhloglomeris Verhoeff, 1898 15. Typhloglomeris lohmanderi (Golovatch, 1989) C  (Lignau, 1903) W, C + 20-2200, se Ca Lignau 1903, Read 1992 63. C. pterophylacum Read, 1992 W, C + 20-1600, se Ca Read 1992, Zuev 2014 64. C. quadrus Read, 1992 W, C 700-1000, e Ca Read 1992 65. C. ruber (Lignau, 1903) W + 100-2000, se Ca Lignau 1903, 1915, Read 199266. C. schestoperovi Lohmander, 1936  All species of Polyzoniida, Siphonocryptida, Glomerida and Chordeumatida, as well as most species of Julida and Polydesmida appear to be native, endemic or subendemic, but the genera and families they represent are widely distributed across the Euro-Mediterranean Realm. As a result, endemism is profound at the species and, to a lesser degree, generic levels. Most of the species (86, or 83%) show a Caucasian distribution pattern, thus being endemic or subendemic to the Caucasus region. The same pattern was found at the generic level, with 18 genera being endemic or subendemic to the Caucasus, including all 14 genera of the order Chordeumatida that inhabit the region Makarov 2016, Antić et al. 2018). There are neither families nor orders of Diplopoda that are confined to the Caucasus region alone.
This picture is hardly surprising, as due to the proximity to the Black Sea the climate of western Georgia is largely humid warm temperate. More easterly, the climate is increasingly dry and hot, already dominating eastern Georgia (Bondyrev et al. 2015). Following this trend, the millipede fauna is increasingly depauperate: at least 79 diplopod species occur in western Georgia (= Colchis), but this number drops down to 37 in the central and to 25 in the eastern parts of Georgia (Table 1,  . Millipedes are mainly confined to forests in the Caucasus and in Georgia reflecting their terrestrial, meso-to hygrophilous, largely also calciphilous, arthropod relationships which are historically, trophically and ecologically closely associated with forested biomes (Golovatch and Kime 2009). Dry steppes and arid light forests in central and eastern Georgia (Table 2), as well as the Colchidan swamps of western Georgia support only very few millipede species. Especially tolerant to xeric conditions    seems to be Leptoiulus tanymorphus (Attems, 1901) (Fig. 12), whereas both Hirudisoma roseum (Victor, 1839) and Julus colchicus Lohmander, 1936 (Fig. 6), as well as several Chordeumatida tend to represent particularly hydrophilous epigean species. Nearly all cavernicoles (e.g., Leucogeorgia spp.) are likewise highly hydrophilous. As noted above, due to the quite extensive karsts that blanket much of western Georgia, in particular Abkhazia, Samegrelo, Racha Lechkhumi and Imereti, a large proportion of the total fauna is taken up by true cavernicoles (14 species, or 13%). The bulk, however, remains forest-dwelling millipedes and their woody habitats mainly are more or less montane. Present-day Georgia enjoys a remarkable network of nature reserves and national parks, with more than 1/3 of the entire national territory still   covered with mountain forests. In contrast, its lowland woodlands have largely been destroyed and long replaced by agri-or sylvicultures, as well as orchards and vineyards (https://apa.gov.ge/en/protected-areas/national-park).
Following Gulisashvili (1964) and Nakhutsrishvili (2013), the altitudinal nature zonation of Georgia can crudely be presented in a tabular form ( Table 2). The zonation varies quite clearly in different parts of Georgia (Fig. 1) in relation to climatic gradients. Central Georgia (Figs 1, 4), which is climatically closer to the eastern part of the country, warrants recognition as a separate entity based at least on the distribution of several endemic or subendemic species of Diplopoda (Fig. 11).
No transects are contained in Figures 6-12 to avoid an "overcrowded" presentation of the numerous species distributions; however, these are easy to extrapolate from the figures and thus to follow the general trends and variations in the macro relief of the corresponding parts of Georgia. Only relatively few millipedes occur in subalpine to alpine environments (usually ≥ 2200 m a.s.l.) in Georgia (Table 2). Yet nearly none of them can be considered as being characteristic of the high altitudes, because the same species appear to populate lower elevations as well, down to almost sea-level: Caucaseuma variabile Antić & Makarov, 2016, Dentatosoma magnum Antić & Makarov, 2016  Metamastigophorophyllon hamatum Antić & Makarov, 2016, Chaetoleptophyllum flexum Golovatch, 1979, Cylindroiulus placidus (Lignau, 1903), Strongylosoma kordylamythrum Attems, 1898, Brachydesmus assimilis Lohmander, 1936, B. kalischewskyi Lignau, 1915, Polydesmus abchasius Attems, 1899and P. lignaui Lohmander, 1936. The same concerns Omobrachyiulus brachyurus (Attems, 1899) and Catamicrophyllum caucasicum (Attems, 1901), both of which occur also at ≤ 2500 m a.s.l. in the Caucasus Minor of Armenia and Azerbaijan; the former species also in Dagestan, Russia, Caucasus Major (personal observations). Nopoiulus kochii (Gervais, 1847) is a subcosmpolitan species, common also throughout the Caucasus (10-2200 m a.s.l., Table 1), but because the entire genus Nopoiulus is particularly diverse in the Caucasus region, the latter could well have also been the origin centre of N. kochii (Golovatch and Enghoff 1990).
At the present, the only exception that may possibly be referred to as a high-montane element in the fauna of Georgia, as well as the entire Caucasus, seems to be Alpinella waltheri Antić & Makarov, 2016 (2860 m a.s.l., Table 1, Map 12). Even though some species of Julus, i.e., Julus colchicus Lohmander, 1936 (20-2850 m a.s.l.), J. kubanus Lohmander, 1936 (300-2100 m a.s.l.) and J. lindholmi Lohmander, 1936 (450-2200 m a.s.l., Table 1, Figs 9, 12), mostly occur over a wide range of altitudes, J. lignaui Verhoeff, 1910 (1500-2800 m a.s.l.) is perhaps the sole congener that seems to be inclined to dwelling in high-mountain environments. However, the paucity or even absence of unequivocally high-mountain elements in the Caucasus generally, and in Georgia in particular, requires confirmation, as our knowledge of the millipede fauna of the regions concerned is still far from complete.

Conclusion
Ongoing research on the diplopod fauna of Georgia will undoubtedly reveal many more species and refine their distributions. This particularly concerns several genera of Julidae, including new cavernicolous and epigean ones (D. Antić, A. Evsyukov, B. Vagalinski, personal communications). As a result, the present paper must only be taken as provisional, marking the present state of the art and is certain to be updated in the near future.