Taxonomic status of Syngamus nematodes parasitizing passeriform hosts from Central Europe: Morphological,...

The systematic position and validity of species within genus Syngamus have always been controversial. In this present work, we evaluated the taxonomic status and phylogenetic relationships between three species of Syngamus nematodes (Syngamus trachea, Syngamus taiga and Syngamus merulae) and one taxa, determined only to the generic level, collected from respiratory tracts of passeriform hosts from Central Europe using newly obtained sequences of 2 nuclear markers (internal transcribed spacers 1 and 2 [ITS1, ITS2]) and a fragment of mitochondrial cytochrome oxidase I [COI] gene. Our results clearly showed that S. trachea, S. taiga and S. merulae are valid, molecularly and morphologically distinct species. Moreover, molecular analysis of adult female of Syngamus sp. collected from tracheae of the European robin Erithacus rubecula clearly indicate that these comprise separate species. In the derived phylogeny, the Syngamus clade is divided into two sub-clades: one comprised Syngamus species with a characteristic, well-developed cuticular collar around the oral opening (S. trachea and S. taiga) and a second that groups taxa without or with rudimentary collar (S. merulae and currently sequenced Syngamus sp. from Erithacus rubecula). These results clearly suggest that the degree of collar development (well-developed vs. rudimentary/absent) may be an important phylogenetic feature for determining the structure of the genus Syngamus on subgeneric level. Additionally, our results support historical division of the genus Syngamus into two subgenera S. (Syngamus) and S. (Ornithogamus).