Dragonflies and damselflies (Odonata) from Flores Island, Lesser Sunda Archipelago: New occurrences in extreme environments and an island-level checklist of this group

Although the Odonata are common inhabitants of various extreme environments such as geothermal springs, brackish wetlands, mangroves, and volcanic lakes, the assemblages of this group associated with extreme habitats in Australasia are rather poorly known. Here, we combine museum collection data and published reports on Odonata from extreme habitats on Flores Island, Lesser Sunda Archipelago. The highly acidic Sano Nggoang Crater Lake (mean pH = 3.17) on Flores houses seven species as follows: Agriocnemis pygmaea, Xiphiagrion cyanomelas (Coenagrionidae), Neurothemis ramburii, Orthetrum pruinosum pruinosum, O. sabina, O. testaceum soembanum (Libellulidae), and Anax gibbosulus (Aeshnidae). A coastal marsh site with slightly brackish water on Flores harbors at least five dragonfly species as follows: Diplacodes trivialis, Neurothemis intermedia excelsa, N. terminata, Pantala flavescens, and Rhyothemis phyllis ixias (Libellulidae). The migratory dragonfly Pantala flavescens was a single species recorded on the waterless Kanawa Island near the western edge of Flores. Our findings suggest that extreme habitats in eastern Indonesia primarily colonized by widespread generalist Odonata species. Finally, an updated checklist of Odonata species recorded from Flores Island was compiled. Our survey of museum specimens recovered two species not found on existing species lists for Flores: Neurothemis intermedia excelsa and Pantala flavescens.


Introduction
The order Odonata (dragonflies and damselflies) contains not less than 5,900 species globally (Kalkman et al. 2008;Van Tol 2020). These insects are able to colonize a wide array of extreme environments such as hot springs, acidic, alkaline, sulfide, and hypoxic water bodies, salt-water wetlands and mangroves, and ephemeral wetlands and pools (Brues 1924;Corbet 2004).
Odonata was considered one of the four insect orders (the others being Diptera, Coleoptera, and Hemiptera) that commonly occur in hot springs around the World (Pritchard 1991). There is a large body of Figure 1. Map of the localities with extreme habitats on Flores and Kanawa islands (Lesser Sunda Archipelago, Indonesia), from which available museum lots were sampled: Sano Nggoang Lake (1); coastal marsh near Labuan Bajo on Flores Island (2); and Kanawa Island (3). Site 1. Sano Nggoang Lake [8. 7093°S, 119.9975°E]. This is a large crater lake (size of 3.3×2.2 km) situated in the center of the Waesano Stratovolcano, West Flores ( Fig. 2A). It has a maximum depth of 500 m, being the deepest volcanic lake in eastern Indonesia (ESIA 2019). Based on a published report, the lake's waters are highly acidic (mean pH = 3.17; range 2. 81-3.85 Site 2. Small coastal marsh [8.5220°S, 119.8704°E] near Labuan Bajo on Flores. This site contained a shallow reed marsh of 100×100 m in size having a slightly brackish water and situated ca. 30 m away from the shoreline (Fig. 2B). This marsh was destroyed due to the reconstruction of Bajo Komodo Ecolodge in 2018 (I. Bolotov, pers. observ.).
Site 3. Kanawa Island [8.4926°S,119.7575°E]. This is a small island, 500×730 m, situated 9 km away from the western edge of Flores. The maximum altitude is 60 m. The island is covered by dry grass savanna with Indian jujube (Ziziphus mauritiana) and tamarind (Tamarindus indica) (Bolotov et al. 2018a). It does not house permanent water bodies but small seasonal marshes are present in its western and northern parts during the rainy season (Fig. 2C).

Occurrences of Odonata from extreme environments on Flores
The extreme habitats on Flores Island support species-poor Odonata assemblages. Based on available museum lots, three species were recorded on the shore of the Sano Nggoang Lake [site 1], i.e. the dragonfly Orthetrum sabina, and damselflies Agriocnemis pygmaea and Xiphiagrion cyanomelas (Figs 3-5).
Distribution: Seychelles, India, Sri Lanka, mainland Southeast Asia, China, Japan, Indonesian Archipelago, the Philippines, New Guinea, Solomon Islands, Australia, and the Fiji Islands (Steinmann 1997b). Earlier records from Flores: Unknown. To the best of our knowledge, the present study reports on the first record of Neurothemis intermedia excelsa from this island.
Comments: This subspecies can be distinguished from other geographic races be the combination of the following characters: coloration of the wing base does not reach triangle in the forewing and extends to triangle in the hindwing (male); coloration of the wing base restricted to innermost cells (female) (Seehausen & Günther 2016).
Comments: The primary diagnostic feature of this subspecies is the darker face and blackish labium (Fig. 10C, 10F) (vs almost yellow in the nominate subspecies) (Seehausen et al. 2018).

Brief review of the Odonata fauna on Flores
This study brings the total Odonata fauna of Flores Island to 46 species (16 Zygopteran and 30 Anisopteran taxa) (Table 1). Two species recovered on Flores for the first time, i.e. Neurothemis intermedia excelsa and Pantala flavescens. The dragonfly species richness on Flores is similar to that on Timor (approximately 40 species) (Seehausen et al. 2018), but much less than that on Sumba, which has more than 70 species (Lieftinck 1953).
Most Odonata taxa in the fauna of Flores are widespread species sharing clear affinities to the Oriental Region (30 species, 65% of the total species richness), while 15 species and subspecies (32%) can be considered endemic to the region (Table 1). The ranges of the latter group expand throughout the Lesser Sunda Islands (two species are also known to occur on Java) or restricted to the eastern insular group of this archipelago (i.e. the East Nusa Tenggara Region). Among these endemic taxa, two species are unknown beyond Flores, i.e. Drepanosticta floresiana and Indolestes floresianus, although their distribution needs further study (Lieftinck 1939(Lieftinck , 1953(Lieftinck , 1960. Finally, Hemicordulia australiae represents the single species of probably Papuan-Australian origin on Flores (2%) (Kalkman et al. 2008).

Odonata populations in extremely acidic water bodies in Indonesia and beyond
The Sano Nggoang Lake represents a deep, acidic, and brackish water body enriched by nitrogen and sulphur (see Material and methods). Available museum collections indicate that the shallow coastal areas of this crater lake (pH below 3.9) house viable populations of Orthetrum sabina, Agriocnemis pygmaea, and Xiphiagrion cyanomelas. Additionally, Orthetrum pruinosum pruinosum, O. testaceum soembanum, Neurothemis ramburii, and Anax gibbosulus were recorded from this lake based on published data (Lieftinck 1936). In summary, the Odonata fauna of this acidic lake on Flores contains seven widespread, generalist species. The damselfly Xiphiagrion cyanomelas and the skimmer Orthetrum sabina were common species in this caldera in 1929 and 2015. Agriocnemis pygmaea did not occur in 1929, but this diminutive species may have been overlooked, as it was on Timor (Seehausen et al. 2018). The other species were not rediscovered in 2015. It should be mentioned that the larvae of Xiphiagrion cyanomelas and Orthetrum pruinosum were also found in Lake Linow, an acidic, geothermal water body in northern Sulawesi (temperature 27.8°C, pH 4.0; 05.vi.1932) (Lieftinck 1936).
The Sano Nggoang and Linow lakes in eastern Indonesia are rather unusual examples of successful colonization of highly acidic environments by dragonflies. Typically, these insects cannot colonize extremely acidic water bodies. This is most likely associated with negative effects of low pH (below 4.0) on the survivorship, predation, respiration rate, and fitness of dragonfly nymphs (Gorham & Vodopich 1992), although the eggs of dragonflies seem to be resistant to acidic waters and can tolerate pH 3.5 without significant shifts in the development times and hatching success (Hudson & Berrill 1986;Rychła et al. 2011). Only chironomids were recorded in the acidic Banyupahit-Banyuputih River (pH below 3.5) flowing from the Kawah Ijen Crater Lake in East Java, Indonesia (Löhr et al. 2006). Odonata were absent in highly acidic (pH below 3.0) mining lakes in the Muskau Arch area at the Germany-Poland border (Rychła et al. 2011), while Coenagrion mercuriale (Charpentier, 1840) was found in such a lake (pH 3.0) near Grünewalde in eastern Germany (Rodrigues & Scharf 2001). However, water bodies with a slightly higher pH can host dragonfly assemblages with several acid-tolerant species, e.g. the Adirondack lakes in North America (pH 4.0-6.0) (Frolich Strong & Robinson 2004) and small forest lakes in Europe (pH 4.2-5.0) (Mossberg & Nyberg 1979). It was shown that pH is a primary environmental filter of dragonfly assemblages controlling site-to-site shifts in their phylogenetic structure across biomes (Arrowsmith et al. 2018).

Dragonflies in coastal marshes and on small waterless islands
The coastal marsh site near Labuan Bajo on Flores supported at least five species, i.e. Diplacodes trivialis, Neurothemis intermedia excelsa, N. terminata, Pantala flavescens, and Rhyothemis phyllis ixias. The majority of these taxa represent widespread generalist species, a pattern consistent with findings from coastal wetlands in North America (Wright 1943;McCreadie et al. 2005;Catling et al. 2006, Catling 2009) and Europe (Uboni et al. 2020). In particular, diverse assemblages of odonates exploit brackish pools and salt marshes from Quebec and New Brunswick in Canada to the deltas of the Mississippi and Mobile rivers/Tensaw on the Gulf of Mexico (Wright 1943;McCreadie et al. 2005;Catling et al. 2006, Catling 2009). It was shown that at least 15 widespread Odonata species inhabit brackish wetlands in Europe (Uboni et al. 2020). Saline inland lakes in North America can also support rather species-poor Odonata assemblages, comprising a few common, generalist species (Schwarz 1891;Osburn 1906;Cannings & Cannings 1987). The dragonfly Erythrodiplax berenice (Drury, 1773) (Libellulidae) can breed in seawater and is a common inhabitant of salt-water marches and ponds in eastern North America (Osburn 1906;Dunson 1980;Dunson & Travis 1994). The mangrove skimmer Orthetrum poecilops Ris, 1919 (Libellulidae) is another coastal specialist from East Asia that can breed in salt water (Wilson 2020). Recently, Mortonagrion megabinluyog Dow & Choong, 2015 (Coenagrionidae), a possible example of coastal species with restricted range, was described from coastal mangroves of Brunei on Borneo (Dow & Choong 2015).
Record of Pantala flavescens from the Kanawa Island in April (dry season) aligns with available data on high migratory abilities of this dragonfly. This migratory species was recorded repeatedly on islands, which lack surface fresh water, e.g. Beihuang Island in China (Cao et al. 2018), Ngulu Atoll in Micronesia (Buden 2010), and Maldives (Hobson et al. 2012). It was shown that arrival of Pantala flavescens to Maldives and Seychelles is a part of its annual migration through the western Indian Ocean from India to East Africa (Anderson 2009;Hobson et al. 2012). Conversely, small waterless islands can support dragonfly development during the rainy season when seasonal marshes and pools emerge in various depressions. It was shown that dragonflies and other aquatic invertebrates rapidly colonized even small temporary pools such as rainwater-filled elephant footprints in the Kibale National Park, Uganda, East Africa (Remmers et al. 2017).

Conclusion
 The Odonata colonizing extreme environments such as acidic lakes and seaside habitats in eastern Indonesia are primarily widespread generalist species.  Species-poor dragonfly assemblages were recovered from extreme habitats in eastern Indonesia for the first time. The highly acidic Sano Nggoang Crater Lake on Flores supported seven species, while a small coastal marsh site on the shore of this island harbored five species. One migratory species was found on a waterless islet near the eastern edge of Flores.  The Odonata fauna of Flores Island contains 46 species, with 16 Zygopteran and 30 Anisopteran taxa. Our research of museum specimens recovered two species new to the fauna of Flores: Neurothemis intermedia excelsa and Pantala flavescens. The Odonata species richness estimate on Flores is comparable with that on Timor but much lower than that on Sumba.