Towards a phylogeny of Cyclops (Copepoda): (in)congruences among morphology, molecules and zoogeography

The phylogeny of Cyclops (similar to 30 spp.), a predominantly Palearctic cold-adapted genus, was reconstructed based on morphological and molecular characters. The morphological analysis used extensive taxon sampling from the entire Holarctic range of the genus and included 53 morphological characters. Polymorphic traits were coded by the "unordered," "unscaled" and "scaled" methods; maximum parsimony criterion was applied in tree building. Molecular phylogenetic reconstructions utilized partial nuclear 18S and 28S ribosomal genes, mitochondrial cytochrome oxidase I and complete internal transcribed spacer regions I and II, albeit with limited taxon sampling. Bayesian inference and maximum likelihood were used in these tree reconstructions. The molecular characters were used both in combination with morphology and as an independent test of the basal relationships inferred from morphology. Monophyly of the genus received strong support in both the morphological and molecular phylogenies; the basal relationships remain unresolved. The morphology-based phylogenies, along with the geographic distribution patterns and ecological traits, supported monophyly of the ankyrae-ladakanus clade, scutifer-clade (C. scutifer, C. jashnovi, C. columbianus), kolensis-clade (C. kolensis, C. kikuchii, C. vicinus, C. furcifer, C. insignis, C. alaskaensis), abyssorum-clade (C. abyssorum s. str., C. abyssorum larianus, C. ricae, C. sevani) and divergens-clade (South Carpathian "Cyclops sp. Y," C. mauritaniae, C. divergens, C. bohater, C. lacustris). Relationships among European and North American populations of C. scutifer and C. columbianus based on partial sequences of the 12S mitochondrial gene show C. scutifer to be paraphyletic, suggesting two independent invasions into North America via the Bering Land Bridge from Siberia to Alaska.