Integrative taxonomy confirms two new West-Palaearctic species allied with Chrysotoxum vernale Loew, 1841 (Diptera: Syrphidae)

The taxonomy of the syrphid genus Chrysotoxum Meigen, 1803 (Diptera: Syrphidae), is complex and currently under scrutiny. Two new species allied with Chrysotoxum vernale, one from the Western Mediterranean, Chrysotoxum hispanicum sp. n. and the other from the Eastern Mediterranean, Chysotoxum anatolicum sp. n., are described and illustrated. Chrysotoxum hispanicum sp. n. is distinguished from the similar C. vernale Loew by the size of the yellow abdominal fasciae and shape of surstyli. Chrysotoxum anatolicum sp. n., known only from females, possesses an almost entirely yellow-pigmented wing, unusual amongst the other studied species of the C. vernale group. Additionally, C. hispanicum sp. n. and C. anatolicum sp. n. are separated from each other, as well as from other species of the C. vernale group by COI and ITS2 gene markers. An identification key to the West Palaearctic species of the C. vernale group is provided.


Introduction
Within the family Syrphidae (Diptera), the subfamily Syrphinae (syrphines) consists of four tribes and 57 genera, 42 of which belong to the widespread tribe Syrphini (Mengual et al. 2008). Chrysotoxum Meigen, 1803, is one of the most distinctive Syrphini genera, with adults appearing as Batesian mimics of social wasps due to their long antennae, black and yellow bodies and oval to elongate, convex abdomens (Van Veen 2004). Larval biology is poorly known, but some species have been recorded in association with ant-attended root aphids (Aphididae) Electronic supplementary material The online version of this article (https://doi.org/10.1007/s13127-020-00465-w) contains supplementary material, which is available to authorized users. (Rotheray 1993). According to molecular phylogenetic work, Chrysotoxum is near Epistrophe Walker, 1852;Epistrophella Dušek et Láska, 1967;andXanthogramma Schiner, 1861 (Mengual et al. 2008).
Chrysotoxum is widespread over all biogeographic regions except for Australasia and Antarctica, but is most speciose in the Palaearctic region with 85 described species (Thompson and Rotheray 1998;Mutin and Barkalov 1999;Huo and Zheng 2004;Huo et al. 2006Nedeljković et al. 2013Nedeljković et al. , 2015Nedeljković et al. , 2018aVujić et al. 2017). In the Western Palaearctic, i.e. excluding China and the Russian Far East (Lattin 1967;Van Steenis and Lucas 2011), there are 78 species, 13 of which are present in the Iberian Peninsula (Van Eck 2011; Ricarte and Marcos-García 2017) and 18 in Turkey, including the Anatolian Peninsula (Sarıbıyık 2014;Vujić et al. 2017;Nedeljković et al. 2018a). Iberian species of Chrysotoxum have not been revised yet, while those of the Balkan and Anatolian peninsulas have experienced scrutiny in recent years, with seven new species erected (Nedeljković et al. 2013(Nedeljković et al. , 2015(Nedeljković et al. , 2018aVujić et al. 2017).
Although identification of Chrysotoxum is usually straightforward at the genus level, separation of some species has proven difficult and often dependent on subtle morphological characters and molecular, morphometric or even ecological analyses (e.g. Nedeljković et al. 2013Nedeljković et al. , 2015. In fact, some individual species have been split into more than one taxon (a species complex) as a product of an integrative study of their taxonomy. This is the case, for example, of Chrysotoxum vernale Loew, 1841, and the similar Chrysotoxum montanum Nedeljković et Vujić in Nedeljković et al. (2015) described from the Balkans.
The species C. vernale was regarded as part of the species group of Chrysotoxum festivum (Linnaeus, 1758) by Masetti et al. (2006). However, Nedeljković et al. (2015) and Vujić et al. (2017) started developing an implicit morphological concept of the C. vernale group for the species sharing a basoflagellomere shorter than scape and pedicel combined, pro-and mesofemora black basally and abdominal terga with yellow fasciae not reaching the lateral margins. Nonetheless, the bases of the pro-and mesofemora are sometimes dark yellow or with brown markings in C. orthostylum Vujić in Nedeljković et al. (2015).
Using both morphological and molecular characters, we examined Spanish and Turkish material of the C. vernale species group to determine its taxonomic status. Descriptions are provided for two new species, as well as a key to the Western Palaearctic species allied with C. vernale. The aim of this paper is to provide further steps in resolving the systematics of the genus Chrysotoxum by diagnosing and differentiating new taxa of the C. vernale group from the Western Palaearctic.

Examined material
A total of 52 specimens belonging to two potentially-new species were examined. These putative new species were compared with other species similar to C. vernale (Nedeljković et al. 2015;Vujić et al. 2017). The examined material is deposited in the following collections: Department of Biology and Ecology, Faculty of Sciences, University of Novi Sad (FSUNS); CIBIO Institute, University of Alicante, Spain (CEUA); Dieter Doczkal's private collection, Germany (DD). Acronyms of the repository collections are presented between square brackets ('[]') after each series of specimens. Square brackets are also used when some additional information is provided, apart from that shown in the printed label. Abbreviations of the Spanish provinces, given between brackets in the examined material list, are as follows: CC, Cáceres; CR, Ciudad Real; GR, Granada; LE, León; O, Asturias; S, Santander; SA, Salamanca; V, Valencia. For location of the Spanish provinces, see map in Ricarte and Marcos-García (2017 (232)]. The fieldwork did not involve redlisted species, neither species protected in legislation.

Morphological study
To describe and diagnose species, characters were examined using a Nikon SMZ 745T and a Leica MZ12 binocular microscopes. Colour characters always refer to dry specimens. Body size was measured as the length ('L') from the tip of the frontal prominence (excluding antennae) to the tip of the abdomen. The proportional length of the antennal segments is given as a ratio ('r') of x/y/z ('x', scape; 'y', pedicel; 'z', basoflagellomere). The length of each antennal segment was measured along its dorsal edge.
Male genitalia were removed from relaxed specimens and stored in microvials containing glycerol, after clearing in warm 10% KOH for 3-5 min and then washing in acetic acid, followed by ethanol, to neutralize KOH. Species were illustrated with photos produced as stacks of individual images made with a camera (Leica DFC 450) attached to a binocular stereomicroscope (Leica M205 C). Stacks and measurements were made with Leica Application Suite X (LAS X) ®, v. 3.0.4.16529. Morphological terms follow Thompson (1999), except for the term 'proepimeron', which follows Speight and Sarthou (2017). 'Tergum' is abbreviated as 'T' and 'sternum' as 'S' in the species descriptions and diagnoses.
New species were described based on the holotypes to warranty the stability of our species concepts by providing an unequivocal correlation between the descriptions and the name-bearing types (holotypes). The intraspecific variability found within the type series of each new species is recorded and included in different ways in the diagnoses, identification key and discussion.

Molecular study
In addition to the morphological character description, we performed molecular analyses using sequences from the 3'COI region and the ITS2 region. We used the same matrix of concatenated COI and ITS2 sequences as in Nedeljković et al. (2018a) upgraded with the additional sequences of C. vernale group specimens. For detailed information on analysed specimens, see Table 1.
Protocols for DNA extraction, PCR amplification and sequencing of 3'COI and ITS2 regions are described in Nedeljković et al. (2018b). The newly-produced DNA sequences were edited for base-calling errors using BioEdit version 7.2.5. (Hall 1999). The rest of the sequences were downloaded from GenBank. COI sequences were aligned manually, whereas ITS2 sequences were aligned using the E-INS-I strategy as implemented in MAFFT v. 7 (Katoh and Standley 2013). Maximum-parsimony (MP) and maximumlikelihood (ML) phylogenetic trees were constructed for COI sequence matrix and for combined matrix of COI and ITS2 sequences. Parsimony analysis was performed in NONA (Goloboff 1999), spawned with the aid of ASADO (Nixon 2008) using the heuristic search algorithm with 1000 random addition replicates (mult_1000), holding 100 trees per round (hold/100), max trees set to 100,000 and applying tree-bisection-reconnection branch swapping. The ML tree was constructed using RAxML 8.2.8 (Stamatakis 2014) using the CIPRES Science Gateway web portal (Miller et al. 2010) under the general time-reversible (GTR) evolutionary model with a gamma distribution (GTRGAMMA) (Rodríguez et al. 1990). The bootstrap support values for clades were calculated with 1000 replicates for both MP and ML trees. The uncorrected pairwise distance (p) matrix for COI gene sequences and a number of variable positions were estimated using MEGA 7 software (Kumar et al. 2016). The trees were rooted on Melanostoma mellinum (Linnaeus, 1758) (GenBank accession numbers: KJ848101 for COI, KJ848059 for ITS2).

New species of the Chrysotoxum vernale group
The two new species described here belong to the C. vernale species group as defined in the introduction. Additional material of other species. Specimens of C. vernale and C. montanum, including types, published in Nedeljković et al. (2015).
Remarks. The other species of the C. vernale group, including C. hispanicum sp. n., have at least posterior half of wing without pigmentation. Chrysotoxum anatolicum sp. n. can also be separated from the similar C. vernale by the shape of the frontal pollinose maculae, bar-shaped in C. anatolicum sp. n. (Fig. 1a) but triangular in C. vernale [ Figure 5D in Vujić et al. (2017)], and colour of the posterior margin of T3, wholly black in C. anatolicum sp. n. but at least with a small central yellow macula in C. vernale.
Description. Female. L = 14 mm. Head (Figs. 1a, 2). Eye with sparse, straight, yellow pile; frons shiny black, with short, black pile and with two separate, bar-shaped, white pollinose maculae (Fig. 1a); ocellar triangle equilateral, shiny black with short black pile; occiput shiny black behind the ocellar triangle and white pollinose in other parts, narrowly yellow ventrally, with yellow pile intermixed with black pile dorsally; antenna black; scape and pedicel with black pile; r = 1:0.62:1.45; arista bare, dark brown; face yellow, with yellow pile; face with a medial black vitta extending from antennal base to mouth edge; facial vitta as wide as a third of the facial width; face black postero-ventrally; gena yellow pilose, entirely shiny black (Fig. 2).
Thorax. Scutum black, with two medial, silvery, pollinose vittae extending for a third of the scutum length from its anterior margin, with short black pile; pleuron shiny black, except yellow maculae on posterior anepisternum and katatergum; katepisternum wholly black; scutellum yellow, except black on lateral corners and a medial macula; scutellum with short black pile; legs yellow except black on basal thirds of pro-and mesofemora; metafemur yellow; wing (Fig. 4a) membrane extensively microtrichose; wing cells R 1 and R 2+3 dark yellow pigmented basally and dark brown to black pigmented apically; cells R 4+5 and DM dark brown to black pigmented; cell CuA 1 dark brown pigmented; cells R and BM dark yellow pigmented; CuP yellow pigmented; calypter yellow with yellow pile at edge; halter dark brown basally, the remainder yellow, with lighter capitulum. Abdomen (Fig. 5a). Shiny black, with short black pile, except for T1 and anterior part of T2 having long yellow and black pile intermixed; all terga with two separate, elongate, yellow maculae not reaching the lateral margins; yellow maculae bearing yellow pile; all sterna shiny black, with short yellow pile anteriorly and black pile posteriorly; S3 with two interconnected yellow maculae, not reaching the lateral margins; S4 with two yellow maculae not reaching the lateral margins; all sternal markings yellow pilose.
Male. Unknown. Etymology. The specific epithet 'anatolicum' refers to the geographic origin of the specimens of the type series, a locality in the Anatolian Peninsula.
Remarks. Abdomen with yellow maculae on terga much wider than those in C. montanum and C. vernale (Fig. 5d); the longest scutellum pile all yellow (sometimes just 1-2 long black pile present) (Fig. 3a), unlike C. vernale (Fig. 3b) and C. montanum which have all or most of the longest scutellum pile black; male genitalia in dorsal view, with surstylus apex more slender (Fig. 6c) than that in C. vernale (Fig. 6d).
Head. Eye pile straight and yellow; vertical triangle black, with long, yellow pile (sometimes black pile also present anteriorly), white pollinose only in the posterior part of the triangle; frontal triangle about twice as long as region of eye contiguity, shiny black, with eye margins narrowly white pollinose from eye contiguity to antennae; frontal triangle with black pile anteriorly and mostly yellow pile posteriorly; antenna black, scape and pedicel with black pile, basoflagellomere 3.8 times longer than wide elongate and with rounded apex; arista bare and dark brown; r = 1:0.66:1.43; face yellow pilose, yellow with a medial black vitta extending from the antennal bases to the mouth edge; facial black vitta as wide as a fourth of the facial width; mouth edge wholly but narrowly black; gena yellow, also with yellow pile; occiput white pollinose, with long yellow and black pile intermixed dorsally.
Thorax. Scutum black with two medial, silvery pollinose vittae extending from anterior margin for two thirds of the scutum length; scutum with intermixed long and short, yellow pile anteriorly, and with long, yellow and short, black pile posteriorly; pleuron shiny black except with yellow maculae on posterior anepisternum and katatergum; scutellum yellow, except for black lateral corners and a small medial macula, with long yellow pile (Fig. 3a); legs mainly yellow except for the black basal thirds of pro-and mesofemora; metafemora entirely yellow; wing membrane extensively microtrichose; wing cell R 1 brown pigmented apically; cell R 2+3 brown pigmented anteriorly; calypter yellow, with yellow pile at edge; halter yellow, with pedicel darker than capitulum. Abdomen (Fig. 5b). Shiny black, with short black pile, except for the yellow pile on T1, anterior part of T2 and lateral parts of T3-T5; all terga with a yellow fascia interrupted in the middle; T2 yellow fascia as wide as a third of the tergum width; each T3-T5 yellow fasciae nearly as wide as half of the tergum width; yellow fasciae on terga with yellow pile; posterior margin of T2 black; posterior margin of T3 with a medial, narrow, yellow macula; posterior margin of T4 with a narrow, yellow fascia; T5 with a semicircular macula on the posterior margin; all sterna shiny black, S1 and anterior part of S2 with long yellow pile; posterior part of S2 and S3-S5 with adpressed black pile; S3 with two interconnected, yellow maculae not reaching the lateral margins; S4 with two yellow maculae not reaching the lateral margins. Genitalia as in Figs. 6a-c. Female (Fig. 5c). Same as the male except for the frons having two separate triangular pollinose maculae on eye margins (Fig. 1b) and the scutum bearing short black pile.
Etymology. The specific epithet 'hispanicum' derives from Hispania, the Latin name for Spain, referring to the type locality of this species. Hispania was a Roman Empire province that also included the current Portugal.
Distribution. Only confirmed from Spain, where it is apparently widespread (provinces: AL, CC, CR, GR, LE, SA, V). It is found mainly in highlands, at altitudes from 500 to 2190 m asl.
Habitats. This species is found in a broad range of habitats, including mixed woodlands of Quercus faginea, Q. pyrenaica and F. angustifolia, and woodlands of Q. pyrenaica, both with temporary brooks and small grassy clearings (Cabañeros national park); 'dehesas' of Q. rotundifolia; croplands next to oak forests (Q. rotundifolia). The holotype was collected in a meadow with a stream in the forests of 'Barranco de las Víboras', Sierra Nevada.

Molecular analysis of the species allied with Chrysotoxum vernale
We analysed 33 COI gene sequences (including the outgroup) of 662 bp in length. The ingroup sequences have 40 variable and 27 parsimony informative positions. The p-distances ratios range from 0.9 to 3%, when comparing COI sequences between different species (Table S1). The topologies of COIbased ML and MP trees do not support the division between the C. festivum and the C. vernale species groups (C. festivum group understood as a set of species with basoflagellomere shorter than scape and pedicel combined and pro-and mesofemora wholly yellow; C. vernale group sensu Introduction). Additionally, C. tomentosum Giglio-Tos, 1890, C. festivum and C. elegans Loew, 1841 are not resolved as separate. Chrysotoxum hispanicum sp. n. forms a nested clade with high bootstrap support (99/98) within the C. vernale clade, while the position of C. anatolicum sp. n. is questionable (Fig. 7a, b).
For the analyses on combined COI+ITS2 sequences, we produced a matrix of 1071 bp. The ingroup sequences have 73 variable positions from which 60 are parsimony informative. ML analysis based on COI+ITS2 resolved the C. vernale species group (C. vernale, C. montanum, C. orthostylum, C. hispanicum sp. n. and C. anatolicum sp. n.) as monophyletic with moderate bootstrap support (82) (Fig. 8a). The new species within C. vernale group, C. anatolicum sp. n. and C. hispanicum sp. n., are also resolved as monophyletic with medium to high clade bootstrap support (87 and 100). Chrysotoxum hispanicum sp. n. clade is nested within C. vernale clade but yet clearly divergent from it. Maximum parsimony analysis based on COI+ITS2 produced four equally parsimonious trees of 279 steps in length (consistency index = 86, retention index = 91). The strict consensus tree shows two main clades (Fig. 8b). The first main clade comprises species of the C. festivum group [ C . b o z d a g e n s i s N e d e l j k o v i ć , V u j i ć e t Hayat in Nedeljković et al. (2018a), C. tomentosum, C. festivum and C. elegans], but the bootstrap support for this clade is below 50. The second main clade comprises the C. vernale group and has low bootstrap support (62). Chrysotoxum anatolicum sp. n. and C. hispanicum sp. n. are resolved as monophyletic with medium to high clade bootstrap support (84 and 99) as on ML tree, and C. hispanicum sp. n. clade is also nested within C. vernale clade.

Key to the Western Palaearctic species of the Chrysotoxum vernale group
The C. vernale group, understood as a set of species sharing a basoflagellomere shorter than scape and pedicel combined, pro-and mesofemora black basally and terga 2-4 with yellow fasciae not reaching the lateral margins, consists now of the following eight species in the Western-Palaearctic: C. anatolicum sp. n., C. antennalis Vujić, Nedeljković et Hayat in Vujić et al. (2017), C. clausseni Vujić, Nedeljković et Hayat in Vujić et al. (2017), C. hispanicum sp. n., C. lineare (Zetterstedt, 1819), C. montanum, C. orthostylum and C. vernale. All species of the C. festivum group ( C . b o z d a g e n s i s , C . e l e g a n s , C . f e s t i v u m a n d C. tomentosum) (Figs. 7, 8), as well as light-legged specimens of C. orthostylum have pro-and mesofemora uniformly yellow or with their bases dark yellow. Light-legged specimens of C. orthostylum would key out with Nedeljković et al. (2015).

Discussion
This study integrates information from both adult morphology and gene sequences to establish species limits within the Western Palaearctic species of the Chrysotoxum vernale group. The results confirmed the presence of two separate Chrysotoxum species at opposite sides of the Mediterannean Basin: C. hispanicum sp. n., from the Iberian Peninsula, and C. anatolicum sp. n., from the Anatolian Peninsula. Chrysotoxum hispanicum sp. n. is distinguished from the similar C. vernale by the relative width of the yellow abdominal maculae, which are wider in relation to each tergum length in C. hispanicum sp. n. (Figs. 5b-c) than in C. vernale (Fig. 5d). The relative width of the yellow abdominal maculae proved to be useful to separate other Chrysotoxum species, for instance, C. festivum/C. tomentosum (Nedeljković et al. 2011(Nedeljković et al. , 2013 and C. bozdagensis/C. octomaculatum/C. elegans (Nedeljković et al. 2018a). The relative width of the abdominal maculae is also used in other syrphine genera such as Dasysyrphus Enderlein, 1938 andEpistrophe Walker, 1852 to separate species (Van Veen 2004;Doczkal and Schmid, 1994). Another useful character to separate C. hispanicum sp. n./C. vernale is the colour of the long scutellum pile, most of which are yellow in C. hispanicum sp. n. (Fig. 3a) and black in C. vernale (Fig. 3b).
Studied specimens of C. anatolicum sp. n. had a remarkable wing pigmentation pattern which covered most of the wing membrane (Fig. 4a), including cells BM, CuP and CuA 1 . The other species of the C. vernale group usually lack pigmentation on the posterior part of wing (Fig. 4b): only a female of C. hispanicum sp. n. was found to have pigmentation in the posterior part of wing but just in the membranous areas next to veins. Similar differences in the wing pigmentation are found in species of other syrphine genera such as Xanthogramma (Nedeljković et al. 2018b) and Leucozona Schiner, 1860(Doczkal 1998, 2000. Another remarkable character in C. anatolicum sp. n. is the gena colour, which is wholly black, while in other species of the C. vernale group is at least partly pale. Nonetheless, some specimens of C. clausseni and C. montanum have a black gena. Recent Chrysotoxum studies such as Nedeljković et al. (2018a) describing C. bozdagensis already showed the utility of a combined COI+ITS2 analysis for species delimitation in this genus. These two markers were also used independently, and with success, for resolving species within the C. festivum and C. vernale groups separately (Masetti et al. 2006;Nedeljković et al. 2013Nedeljković et al. , 2015. However, in this study we showed a limited ability of COI gene sequences in resolving taxonomy of Chrysotoxum species when both C. vernale and C. festivum groups are analysed together. For example, C. festivum and C. tomentosum, both part of the C. festivum group, cannot be delimited using COI, but are resolved as separate using ITS2 sequences (Nedeljković et al. 2013). Thus, only analyses of combined COI and ITS2 sequences can provide successful delimitation of Chrysotoxum species. Unlike COI trees, C. vernale species group is resolved as monophyletic on combined COI+ITS2 trees, although with low to moderate bootstrap support (ML = 82, MP = 62). Additionally, C. hispanicum sp. n. and C. anatolicum sp. n. are resolved as genetically divergent from the other species of C. vernale group (Fig. 8). Chrysotoxum orthostylum does not belong to the C. vernale clade, neither to the C. festivum in the COI-based maximum parsimony tree (Fig. 7b), while in the tree based on COI+ITS2 groups together with species allied with C. festivum (Fig. 8b). In addition, the remarkable shape of the C. orthostylum male genitalia together with the reported variability in colour of pro-and mesofemora (Nedeljković et al. 2015) make the placement of this species difficult in any of the above mentioned species groups. Thus, we decide to leave C. orthostylum as an outlier within the genus Chrysotoxum until further systematic studies are undertaken.
Many syrphid species are rare and/or endemic to the Mediterranean Basin hotspot (e.g. Doczkal 1996;Vujić et al. 1999Vujić et al. , 2001Vujić et al. , 2007Vujić et al. , 2011Marcos-García et al. 2007, 2011Ricarte et al. 2012;Grković et al. 2016), and the two new species described here further contribute to increase the biodiversity of this hotspot. Within the Mediterranean Basin, Turkey and mainland Spain have now a combined total of 24 Chrysotoxum species, 19 in Turkey (Sarıbıyık 2014;Vujić et al. 2017;Nedeljković et al. 2018a;present study) and 14 in mainland Spain (Ricarte and Marcos-García, 2017;van Steenis et al. 2020;present study). The Spanish provinces of León and Salamanca have the highest numbers of Chrysotoxum species recorded in Spain (8 spp. each) (Ricarte and Marcos-García, 2017; present study), probably due to higher sampling efforts in these provinces. Italy and France equal mainland Spain in the number of Chrysotoxum species (14 spp.), but in countries further north, the numbers reduce to, for example, 11 in Germany, 8 in the UK and 7 in Norway, all three with well-studied hoverfly faunas (Speight et al. 2016). Turkey and mainland Spain share about 35% (8 spp.) of their Chrysotoxum faunas, which is slightly higher than the percentage found in other syrphid genera such as Merodon Meigen (22%) . The number of Chrysotoxum species in the Iberian Peninsula will certainly increase after the C. vernale and other species groups such as that of C. intermedium Meigen, 1822 are revised (Nedeljković et al. in prep).
In Turkey, C. anatolicum sp. n. was found in Bozdağ, which extends as a mountain range (with the peak at 2157 m asl) for about 170 km in an east-west direction between the provinces of İzmir and Manisa (Toksöz and Ustaoğlu 2005). This locality includes forests with ancient chestnut (Castanea sativa), pines (Pinus brutia and Pinus nigra) and oaks (Quercus ithaburensis subsp. macrolepis and Quercus infectoria), Mediterranean scrublands ('macchia') and mountain steppes (Kurtaslan and Demirel 2011;Anlaş et al. 2010), all of them providing habitats and resources for a high diversity of invertebrates such as Coleoptera (Tenebrionidae) (Mercan et al. 2004), Dermaptera (Anlaş et al. 2010), Diptera (Chironomidae and Chaoboridae) and Oligochaeta (Toksöz and Ustaoğl 2005). At the moment, Bozdağ is the only known locality where both C. bozdagensis and C. anatolicum sp. n. occur (Nedeljković et al. 2018a).
Chrysotoxum hispanicum sp. n. is widespread in the Iberian Peninsula and present in a broad variety of habitats. The records of C. vernale, confirmed here to occur in mainland Spain based on morphological evidence, originate from the Cantabrian Mountains (Provinces of Asturias, León and Santander) [Marcos- García (1990) in part], the 'Sistema Central' (Cáceres) [Marcos-García (1986) in part] and the Pyrenees (Huesca) (Marcos-García 1985), all high altitude mountain ranges. In Turkey, C. vernale is also found at high altitudes (2000-3000 m asl.), in the Erzurum Province (Sarıbıyık 2014;Vujić et al. 2017), while C. anatolicum sp. n. is found in highlands but at a lower altitude (1567m). Nonetheless, new studies may contribute to better define the altitudinal range where C. anatolicum sp. n. occurs.
The detailed and often integrative study of the taxonomy of the C. vernale group in other parts of the Western Palaearctic (e.g. Balkan Peninsula) has also resulted in the definition and redefinition of several species concepts, some of them corresponding to new taxa (Nedeljković et al. 2015, Vujić et al. 2017. The present paper represents the first attempt to resolve the taxonomy of the C. vernale group in the Iberian Peninsula. As a result, C. hispanicum sp. n. has been discovered among material that was previously thought to belong to the species C. vernale (Marcos- García 1981García , 1986García , 1990Ricarte and Marcos-García 2008). A higher level of taxonomic scrutiny of adults-i.e. further DNA, geometric morphometric, and ecological analyses in a more extensive study area-of Chrysotoxum populations, as well as a more complete knowledge of their early stages and biology are expected to increase the alpha diversity of this genus in the Iberian Peninsula and other parts of Western Europe (Speight 2018). Data availability statement The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.

Compliance with ethical standards
Conflict of interest The authors declare that they have no conflict of interests.
Ethical approval All applicable international, national and international guidelines for the care and use of animals were followed.
This article does not contain any studies with human participants performed by any of the authors.