Connecting the dots: Bridging genetic and spatial differentiation of the genus Eumerus (Diptera: Syrphidae) in the Mediterranean Basin and Balkans

Unveiling the Mainland vs. Insular Variability of the Eumerus barbarus Species Group (Diptera: Syrphidae) in the Western Mediterranean Basin

Comprising nearly 300 described species, Eumerus Meigen, 1822, is one of the most speciose syrphid genera worldwide, and its taxonomic diversity is remarkable in the Mediterranean basin. The Eumerus barbarus (Coquebert, 1804) group consists of four species in the western Mediterranean. Although the phenotypic variability of this species group has been commented on in previous studies, it has never been contrasted with molecular data. In the present work, the morphological variation found in 300+ specimens of this species group from the western Mediterranean is explored and tested against the COI mitochondrial DNA (mtDNA). The highest phenotypic disparity was found in E. barbarus and Eumerus sulcitibius Rondani 1868. The integrative approach has not revealed cryptic diversity within the species E. barbarus but in E. sulcitibius. As a result, a new species close to E. sulcitibius was discovered, Eumerus sardus Aguado-Aranda, Ricarte & Hauser sp. n., from Sardinia, Italy. The new insular species is here described, illustrated, and discussed. A total of twenty-three haplotypes of COI mtDNA were identified amongst the analyzed Mediterranean specimens of E. barbarus, whereas two and five haplotypes were distinguished in the Iberian specimens of E. sulcitibius and Eumerus gibbosus van Steenis, Hauser & van Zuijen, 2017, respectively. Moreover, the first known barcodes of E. gibbosus and Eumerus schmideggeri van Steenis, Hauser & van Zuijen, 2017 were obtained, and the distribution ranges of all species are mapped. An updated dichotomous key to the males of the E. barbarus group from the western Mediterranean is provided.

High Phenotypic Diversity Does Not Always Hide Taxonomic Diversity: A Study Case with Cheilosia soror (Zetterstedt, 1843) (Diptera: Syrphidae) in the Iberian Peninsula

Comprising nearly 500 species worldwide, Cheilosia Meigen is the largest genus of Syrphidae in the Palaearctic region. Within Cheilosia, phenotypic diversity has been assessed in different species groups, including the group of Cheilosia longula (Zetterstedt, 1838). However, the phenotypic variability of Cheilosia soror (Zetterstedt, 1843), a highly variable member of the C. longula group, has never been assessed in western Europe. In the present work, morphological and molecular analyses were conducted to assess the phenotypic variability found in 300+ specimens of C. soror from the Iberian Peninsula. A total of 16 variable characters were identified and defined for the C. soror morphology, with the highest variation found in the colour of the mesonotum pilosity and the metatibia colour. Morphological variation was assessed against molecular variation based on two molecular markers, one mitochondrial, the 5 $\prime$ end of the cytochrome c oxidase subunit I (COI-5 $\prime$ ), and one nuclear, the large subunit ribosomal DNA (28S). Phylogenetic analyses rendered trees with topologies in disagreement with the defined morphological variation. Two haplotypes were identified amongst the analysed specimens of C. soror, together with a haplotypic variant exclusive to the Iberian region. Potential distributions were used to identify unexplored areas of occurrence of C. soror and other species of the C. longula group in the Iberian Peninsula. Unassessed areas of occurrence of C. soror should be surveyed in the future to confirm the absence of hidden taxonomic diversity within the range of phenotypic variation for this species. Phenotypic variation of the other two Iberian species of the C. longula group, C. longula and C. scutellata (Fallén, 1817), was also assessed to find that they are species with less-variable morphology than C. soror and with molecular characters in accordance with other conspecific populations in Europe. New distributional data are provided for C. soror and C. scutellata from Spain, and a leg abnormality is identified for the first time in C. soror.