The crossroads of molecular, typological and biological species concepts: two new species of Gyrodactylus Nordmann, 1832 (Monogenea: Gyrodactylidae)

Abstract

Nucleotide sequences of nuclear ribosomal DNA internal transcribed spacers (ITS) were used to confirm morphological identification of Gyrodactylus species in Fennoscandia. Three pairs of morphologically similar or cryptic species are compared in this study. G. branchicus Malmberg, 1964 and G. rarus Wegener, 1910, hosted by the sticklebacks Gasterosteus aculeatus L. and Pungitius pungitius (L.), respectively, displayed a genetic divergence of 0.9-1.3% along 774 nucleotides of ITS (Jukes & Cantor distance). G. branchicus isolates from the Baltic, White Sea and Scottish North Sea were invariable, but a Belgian North Sea population with a 0.4% divergence in ITS sequence has been collected. The species status of G. branchicus and G. rarus is supported by host-specificity in sympatric habitats and consistent morphological difference in the marginal hook sickles. Among Gyrodactylus on burbot Lota lota (L.) specimens were collected with their 792 bp long ITS sequences differing by 8.5%. This has led to the splitting of G. lotae Gusev, 1953 into two species, G. lotae and G. alexgusevi n. sp. The species are morphologically separable, and a similar range of variation was found in both the anchors and the marginal hooks in other collections and in the original description. Among G. macronychus-like parasites of minnow Phoxinus phoxinus (L.), divergent ITS sequences indicate two cryptic species. By comparison with the type-specimens, one was identified as G. macronychus Malmberg, 1957; the other is here designated as G. jussii n. sp., differing by 21.8% in 950-973 bp long ITS. The consequences of these findings for the species concept and species identification of Gyrodactylus are discussed.

Description of three new species of Gyrodactylus von Nordmann, 1832 (Monogenea) parasitising Oreochromis niloticus niloticus (L.) and O. mossambicus (Peters) (Cichlidae)

“…Sequencing reactions were carried out on a MegaBace 1000 analysis system (GE Healthcare) using DYEnamic ET dye terminators. The PCR primers and the internal primers ITS1R (5'-ATTTGCGTTCGAGAGACCG-3'), ITS2R (5'-GGTAAT-CACGCTTGAATC-3'), ITSR3A (5'-GAGCCGAGTGATC-CACC), and ITS2F (5'-TGGTGGATCACTCGGCTCA-3') (Matějusová et al 2001, Ziętara andLumme 2003) were used for sequencing. Sequences were proofread and assembled in Vector NTI 10 (Invitrogen) and Mega 4 (Tamura et al 2007) was used to calculate genetic distances.…”

“…These substitutions can be attributed to 24 in ITS1 (12 transitions and 12 transversions) and 18 substitutions in ITS2 (9 transitions and 9 transversions), and in addition 1 indel was found. The large number of differences (42 out of 802) observed in the ITS regions suggests that these two species are different, and although no fixed threshold exists for the separation of Gyrodactylus species, Ziętara and Lumme (2003) suggest that a 1% difference in ITS be used as a cut-off value to delineate species. The hamuli of G. ulinganisus sp.…”

Introgression of distant mitochondria into the genome of Gyrodactylus salaris: Nuclear and mitochondrial markers are necessary to identify parasite strains

“…Based on previous experience, ITS corresponds well to the morphological delineation of the Gyrodactylus species. It has even been suggested that divergence of ITS at about 1% could be used as a pragmatic indicator of conspecificity of sister species (Ziętara and Lumme 2003), because ITS sequences are nearly always homozygous, even when they differ very little between host-specific parasites living in the same environment. The lack of heterozygotes is evidence of sexual isolation (Huyse et al 2004).…”

Identification of Gyrodactylus ectoparasites in Polish salmonid farms by PCR-RFLP of the nuclear ITS segment of ribosomal DNA (Monogenea, Gyrodactylidae)

“…The subunit 1 of the mitochondrial cytochrome oxidase (COI) gene may also be used successfully to differentiate species and local Gyrodactylus strains (Meinilä et al 2002(Meinilä et al , 2004Hansen et al 2003Hansen et al , 2007. Molecular techniques were necessary to discriminate and describe morphologically almost identical species within several Gyrodactylus groups such as G. teuchis versus G. salaris , G. jussii vs. G. macronychus and G. alexgusevi vs. G. lotae (Ziêtara and Lumme 2003), G. pictae vs. G. turnbulli (Cable et al 2005), and a number of G. rugiensis-like and G. arcuatus-like species on marine gobies (Huyse et al 2004) . Molecular discrimination of more than 70 Gyrodactylus species based on the sequences of nuclear rDNA gene cluster encompassing both spacers (ITS1 and ITS2) and 5.8S rRNA gene, proved the region suitable for species identification (Ziêtara 2004, Ziêtara and.…”