Phylogeny of Mesocyclops (Copepoda: Cyclopidae) inferred from morphological characters

Abstract

Evolutionary relationships were investigated in the genus Mesocyclops, a pantropical freshwater cyclopid group. In the phylogenetic analyses that involved all 71 known species, and used 81 morphological characters (265 character states) mainly of the adult females, two different approaches were applied: global parsimony, and a new distance method based upon the recognition of sister-groups on the basis of minimal distances iteratively corrected for unique character states (MICSEQ). In coding of the characters, half of which showed intraspecific variation, the ‘scaled’ method was employed, which assumes that any trait between its absence and fixed presence passes through a polymorphic stage. Impact of the reference points on topology of the trees generated by the parsimony method was tested in three ways where the outgroups comprised: (1) nine species representing six genera of two subfamilies; (2) three species from two genera supposedly not distant from Mesocyclops; and (3) one presumably close and one distant relative of Mesocyclops. The trees generated by the parsimony-based and corrected distance methods agreed as to the monophyly of the following groups: reidae-clade (M. reidae, M. chaci, M. yutsil); rarus-clade (Mesocyclops annae, M. pseudoannae, M. splendidus, M. rarus, M. paludosus, M. darwini, M. dayakorum); annulatus-clade (Mesocyclops intermedius, M. ellipticus, M. paranaensis, M. annulatus, M. tenuisaccus); meridianus-clade (Mesocyclops meridionalis, M. varius, M. venezolanus, M. brasilianus, M. pseudomeridianus, M. meridianus); major-clade (Mesocyclops major, M. pilosus, M. insulensis); dussarti-clade (M. dussarti, M. dadayi, M. isabellae, M. thermocyclopoides); pubiventris-clade (M. pubiventris, M. medialis, M. brooksi, M. notius). A majority of the analyses support a clade of the ‘true’Mesocyclops including all ingroup species except the reidae-group, and point to monophyly of the Old World species lacking medial spine on P1 basipodite. There were, however, some components for which the two procedures, regardless of the outgroup choice and/or character set, suggested different relationships. Basal relationships of Mesocyclops[between M. edax (North and Central America), the Neotropical species (M. longisetus, M. araucanus, M. evadomingoi, meridianus- and annulatus-clade), Old World group (P1 basipodite without medial spine) and the rarus-clade (Old World; P1 basipodite with medial spine)] remained unresolved. © 2006 The Linnean Society of London, Zoological Journal of the Linnean Society, 2006, 147, 1–70.