High endemicity in aquatic dance flies of Corsica, France (Diptera, Empididae, Clinocerinae and Hemerodromiinae), with the description of a new species of Chelipoda

Abstract All known records of aquatic dance flies (Empididae, Clinocerinae: 21 species; Hemerodromiinae: eight species) from the island of Corsica (France) are summarized, including previously unpublished data and data on the newly described species Chelipoda puschae Ivković, Perović & Grootaert, sp. nov. This species was collected during the “La Planète Revisitée Corsica 2019” survey and represents the first description of a new species in the genus Chelipoda from the European–Mediterranean region in more than 180 years. A key to European species of Chelipoda is provided. Including the new species, five species are recorded from Corsica for the first time: Dolichocephala malickyi Wagner, 1995, Dolichocephala oblongoguttata (Dale, 1878), Dolichocephala ocellata (Costa, 1854), Chelifera subangusta Collin, 1961, and Hemerodromia unilineata Zetterstedt, 1842. The new species is described and illustrated, and new records of aquatic dance flies from Corsica are given, with new data on 17 species in eight different genera. At present, 29 species of aquatic dance flies are known from Corsica, with 10 species endemic to the island.


Introduction
The island of Corsica is situated in the Tyrrhenian Sea, about 170 km south of mainland France, about 90 km west of Italy, and separated from Sardinia by the Strait of Bonifacio. Mountains cover about two-thirds of the island, forming a single chain that runs in a north-south direction. Corsica is one of the most important centres of endemism for freshwater invertebrates in Europe (Giudicelli 1975;Ketmaier and Caccone 2013). In terms of its area of about 8700 km 2 , the concentration of endemic species on Corsica is one of the highest in Europe, with most of the endemic species located in spring brooks and streams at higher altitudes (Giudicelli 1975).
The aquatic Empididae (Hemerodromiinae and Clinocerinae) of Corsica have previously been studied on a number of occasions (Becker et al. 1910;Vaillant 1965Vaillant , 1982Wagner 1995). Becker et al. (1910) and Vaillant (1965Vaillant ( , 1982 described, in total, three new species of aquatic dance flies from the island. Pusch (1996) provided the most detailed study of the Clinocerinae of Corsica, describing six new species. At present 23 species of aquatic dance flies are known from Corsica (Becker et al. 1910;Vaillant 1964Vaillant , 1981Wagner 1995;Pusch 1996), with nine endemics (Yang et al. 2007).
Both larval and adult aquatic Empididae are predators, mainly feeding on smaller aquatic dipterans such as Chironomidae, Simuliidae, and Psychodidae (Vaillant 1952(Vaillant , 1967Harkrider 2000;Werner and Pont 2003;Ivković et al. 2007;Ivković and Plant 2015). Adult Hemerodromiinae are easily distinguished from adult Clinocerinae by their raptorial forelegs. They live and hunt in riparian vegetation, whereas adult Clinocerinae are primarily found on the surface of emergent wet stones or in moss mats (Ivković et al. 2007;Sinclair 2008).
Distribution and biodiversity studies are crucial for an understanding of the drivers of biodiversity hotspots (Ivković and Plant 2015;Schmidt-Kloiber et al. 2017). Regional distribution and biodiversity surveys are important for defining the biogeographic distribution of certain species or genera. They also contribute to the study of the various factors that influence changes in biodiversity and that subsequently affect the species conservation status (Meyer and Wagner 2011;Ivković et al. 2013aIvković et al. , 2017Ivković et al. , 2020Shamshev and Ivković 2020).
In this paper, we present new records of aquatic dance flies from Corsica (France) and also describe a new species. Detailed distribution data are presented, all resulting from the examination of specimens collected at 26 sites, sampled during the "La Planète Revisitée Corsica 2019" survey in June 2019.

New specimen records
This paper is largely based on data and specimens obtained during the "La Planète Revisitée Corsica 2019" survey (http://laplaneterevisitee-corse.mnhn.fr/fr/participants-volet-terrestre-2019). This 6 th section of the large-scale biodiversity programme "La Planète Revisitée" or "Our Planet Reviewed" was organized solely by the French National Museum of Natural History (MNHN, Paris). Its primary aim is to rehabilitate taxonomic work that focuses on the largely neglected components of global biodiversity, i.e. invertebrates (both marine and terrestrial). The Corsica survey started in the spring of 2019 and will be concluded during 2021. It has entailed a number of blitz visits of one or two weeks to particular areas, and traps that were operational throughout the season. At the end of June 2019, a team of 10 French and two Belgian researchers conducted fieldwork in the Alta Rocca region in the south, and the Tartagine valley in the north. They employed a large number of sampling techniques including Malaise traps, pan traps of different colours, polytraps, light traps, pitfall traps, and Lindgren funnel traps. Sweep nets and hand collecting were also used. Between June 23 and 26, 2019, 17 sites at four different research locations in the Alta Rocca area (southern Corsica) were selected for pan trap sampling by Marc Pollet. At three locations, four sampling sites were operational and at the main research location, Campu di Bonza (BO), a fifth sampling site was added. In nearly all sampling sites the same sampling strategy was applied: five blue, five yellow and five white pan traps were installed at soil surface level, in five 3-coloured trap sets. They were filled to two-thirds full with a light formalin solution (<5%) and detergent to lower the surface tension. All traps were operational for four consecutive days (27-30 June 2019). A total of 258 pan traps were in operation during this period. In addition, at each of the sampling sites (and also at other places in each location), flies were collected by sweep net and by hand (with a small polymer jar). All specimens included in the present paper were retrieved from the pan trap and sweep net samples, and from the hand collecting.
All sampling sites were georeferenced while sampling. The names of taxa reflect current nomenclature and classifications (Sinclair 1995;Yang et al. 2007). Species of Wiedemannia mentioned herein are not assigned to subgenus, as the subgenera do not represent monophyletic groups and are therefore considered invalid (Ivković et al. 2019). The literature used for identification included Engel (1939Engel ( , 1940, Vaillant (1965Vaillant ( , 1982, Wagner and Horvat (1993), Wagner (1995), and Pusch (1996. Records are listed for each species. A list of sampling sites with latitude, longitude, altitude, and collecting method is presented in Table 1, and a map showing the positions of the georeferenced sampling sites is also provided (Fig. 1). The collected aquatic dance flies were preserved in 75% ethanol solution (EtOH). For identification purposes, in some cases male terminalia were macerated in hot 85% lactic acid, dissected, and stored in 75% ethanol along with the specimen in the same tube. All specimens listed in the Material examined sections were collected by Anja De Braekeleer, Claire Villemant, and Marc Pollet. Taxonomic diversity is considered at the level of subfamily, genus, and species. Label data for primary types are cited in full, with original spelling, punctuation, and dates. This study is based on material housed in the following institutions: National Museum of Natural History, Paris, France (MNHN); Royal Belgian Institute of Natural Sciences, Brussels, Belgium (RBINS); col. M. Ivković, University of Zagreb, Croatia (UZC); and Canadian  Cumming and Wood (2017). The femoral formula is taken from Plant (2009). Homologies of the male terminalia follow those of Sinclair and Cumming (2006) and Plant (2009).

Taxonomy
Sternum yellow, with dark yellow pleura and light brown scutum. Dark brown longitudinal stripe in centre of scutum dorsally broadening towards pronotum and scutellum. Setae on scutum black, with 2 pairs of acrostichal setae, middle pair stronger, posterior pair rather fine and close to scutellum. One anterior pair and one posterior pair of dorsocentral setae, both long and strong. Three notopleural setae, upper posterior rather strong, others smaller and thinner. One pair of strong, marginal scutellar setae.
Wing membrane transparent, veins light brown. Squamae with black fringe. Halter pale brown.
Etymology. The species is named after the German entomologist Martina Pusch, who described six species of Empididae (Clinocerinae) from Corsica.
Remarks. At present, this species is only known from Corsica. It was collected at each of the four localities and eight of the 17 sampling sites investigated during the "La Planète Revisitée Corsica 2019" survey, ranging from open pozzine landscapes to riverbanks in dry oak forests between 845 m and 1,580 m. Chelipoda puschae sp. nov. clearly prefers pine forest (sapinière) (Fig. 5) over the other biotopes sampled, with over 96% of the 387 specimens collected here. Within this forest, the species was collected in greatest numbers at a dry rocky site, where its abundance was over five times as high as in the other more humid sampling sites in the same location. Over 97% of all specimens in the pine forest were retrieved from yellow pan traps, and less than 3% from white and blue pan traps.

New records of aquatic Empididae (Clinocerinae & Hemerodromiinae) from Corsica (France)
The following format is used for the distribution data: Material examined: number of males (♂) and/or females (♀), locality and location name, description of sampling site, collection date or period, collecting method (sampling site ID, see Table 1). Species recorded for the first time for Corsica (France) are indicated with "*" in front of the species names. A full list of sampling sites is given in Table 1.
Remarks. This is the first tentative record of this species for Corsica. Although the wing pattern corresponds exactly to that in Wagner (1995), as this is a female, the identification is not 100% certain. We thus await the discovery of the corresponding male. Remarks. This is the first record of this species for Corsica. Becker et al. (1910) reported Dolichocephala guttata (Haliday, 1833), but this record is doubtful as the wing patterns of both species are almost identical and females are indistinguishable. Unfortunately, there is no information on how many specimens of each sex were collected by Becker et al. (1910). As D. guttata and D. oblongoguttata can be easily confused and/or mixed, the occurrence of D. guttata in Corsica needs to be confirmed. Remarks. Described and recorded for the first time by Vaillant (1964), and also collected by Pusch (1996). Remarks. This species was previously reported by Wagner (1995) and Pusch (1996). This species was reported in Becker et al. (1910) as Röederia longipennis Mik, 1880, which was subsequently synonymized with Wiedemannia zetterstedti (Fallén, 1826). However, this is likely a misidentification since the latter species does not occur in this part of Europe and there are substantial taxonomic misidentifications in the Wiedemannia zetterstedti "group". A taxonomic revision of this group of sibling species is ongoing and hopefully the taxonomic status of all species in this complex will be resolved in the near future. Remarks. Recorded and described by Pusch (1996). Remarks. Reported previously by Becker et al. (1910). Remarks. This is the first record of this species from Corsica.

Discussion
Ten (35%) of the aquatic Empididae recorded from Corsica thus far are considered strictly endemic to the island, and slightly over 40% of the Corsican aquatic empidids are known from other parts of Europe as well (all through Europe, Central Europe, or Southern Europe). The remaining 25% of the species are either widely distributed (Holarctic, Western Palaearctic) or are confined to the Mediterranean area. We compared our list of Corsican species with the existing records of species in Becker et al. (1910), Vaillant (1965, 1982) Wagner (1995, Pusch (1996), Chvála (2012), and Yang et al. (2007). The following six species were not previously recorded from Corsica and represent the first published records: Dolichocephala malickyi Wagner, 1995, D. oblongoguttata (Dale, 1878, D. ocellata (Costa, 1854), Chelifera subangusta Collin, 1961, Hemerodromia unilineata Zetterstedt, 1842, andChelipoda puschae Ivković, Perović &Grootaert, sp. nov. Moreover, this is the first description of a species of Chelipoda from the European-Mediterranean region for more than 180 years.
Of the two subfamilies, the Clinocerinae have a greater species richness in Europe, especially in mountainous areas (Vaillant 1982;Horvat 1995;Ivković et al. 2012Ivković et al. , 2013aIvković et al. , 2013bIvković et al. , 2014Ivković et al. , 2017Ivković et al. , 2020. This agrees with the pattern observed in Corsica and might be explained by the central mountain chain on the island. Likewise, Wiedemannia represents the most speciose genus, both in Corsica and on the continent. By contrast, Chelifera is usually the second most species-rich genus (Meyer and Wagner 2011;Ivković et al. 2013aIvković et al. , 2013bIvković et al. , 2017Ivković et al. , 2020, but in Corsica it is replaced by Kowarzia. A higher diversity of Kowarzia is usually only present in mountain regions (Ivković et al. 2014).
The aquatic Empididae fauna of Corsica is composed of exclusively Western Palaearctic taxa with the exception of Clinocera stagnalis (Haliday, 1833), which is the most widespread Holarctic clinocerine (also known from North America, North Asia, and North Africa) (Sinclair 2008). Most of the Corsican species are restricted to the Central European or Mediterranean regions. However, 10 of the species encountered in Corsica are strictly confined to the island and can therefore be termed endemic. Only five species are shared with the island of Sardinia (Wagner and Horvat 1993;Wagner 1995). We believe that the current species list is far from complete. Indeed, there has not yet been a comprehensive study of Corsica and all of its freshwater habitats. Furthermore, sampling efforts during the "La Planète Revisitée" were restricted to a short period in late spring and only samples from pan traps and sweep net collecting were examined. Some obvious genera such as Bergenstammia and Phaeobalia are currently absent from the list. Species in these genera are usually found on the continent only above 1,000 m a.s.l., and as most of Corsica is montane, it is our belief that more species, including more endemics, are likely to be found in Corsica. Most endemic freshwater insect species in Corsica are restricted to higher altitudes (500-1,900 m) (Giudicelli 1975). The influence of altitude and isolation on biodiversity processes is more marked in Corsica, with 30 peaks exceeding 2,000 m, than in, for example, Sardinia where the highest mountain is only 1,830 m. This could explain, in part, why Corsica has a seemingly higher overall species richness than Sardinia, including aquatic empidids (only nine species), even though Sardinia is almost triple the size of Corsica (Giudicelli 1975;Chvála 2012). When it comes to aquatic empidids, we have to bear in mind that they may have been collected only sporadically in Sardinia, mostly as a side catch during inventories of other aquatic groups (Wagner 1984(Wagner , 1995Wagner and Horvat 1993). Comparisons between the aquatic empidid faunas of Corsica and Sardinia must therefore be made with the utmost caution. However, the greater species richness in Trichoptera, a group with a similar ecological profile to aquatic empidid flies, also sug-gests a richer fauna in Corsica, with more endemic species in Corsica than in Sardinia (Giudicelli 1975). In addition, most endemics are found at higher altitudes in Corsica than at lower altitudes (Giudicelli 1975). Katmaier and Caccone (2013) have stated that Corsica is faunistically impoverished when compared to continental resources. Our results, on the contrary, suggest otherwise as the number of aquatic empidids is quite high, especially considering the limited sampling efforts. It has been assumed that most of the endemic species that now occur in Corsica have differentiated from ancestors on the Iberian Peninsula (Katmaier and Caccone 2013). In aquatic empidids, however, this might not be the case, as most of the species present are shared with Central and Southern Europe and only a minority is shared with the Iberian Peninsula, but detailed morphological and/or genetic studies could confirm or reject this assumption. It is postulated that during the Messinian Salinity Crisis, the Mediterranean Sea almost completely dried up and a number of freshwater species reached Corsica through an area of braided rivers present all over the Mediterranean and connecting Corsica to the European continent (Katmaier and Caccone 2013).
To conclude, we hope that this paper will assist in the understanding of our present-day knowledge of the aquatic empidids of Corsica and will provide a starting point for further, more detailed and comprehensive studies, as well as additional studies in Sardinia where the aquatic dance fly fauna is poorly known.