Molecular phylogeny of Acrobeloides and Cephalobus (Nematoda: Cephalobidae) reveals paraphyletic taxa and recurrent evolution of simple labial morphology

In: Nematology


Members of the family Cephalobidae (Nematoda) are among the most common and morphologically striking soil nematodes. Many members of Cephalobidae have extensive lip elaborations called probolae, but two taxonomically problematic genera, Acrobeloides and Cephalobus, have simple, low probolae. We sequenced a portion of the nuclear large subunit ribosomal DNA for 33 cultures of Acrobeloides and Cephalobus. A phylogenetic analysis of these data, plus sequences representing other members of Cephalobina, revealed a core clade of 22 closely related taxa, but did not represent Acrobeloides and Cephalobus as monophyletic. The dominant feature used in morphological taxonomy of Cephalobidae, the lip region, was homoplastic according to the molecular phylogenetic hypothesis. Contrary to previous suggestions, taxa with simple probolae have arisen multiple times from taxa with complex probolae. Cultures were also examined for mode of reproduction (presumed parthenogenetic vs sexual) and three morphological characters commonly used in generic diagnoses: the shape of the corpus in profile; the number of lateral incisures; and the terminal extent of the lateral field. Most cultures, including all 22 members of the core clade, lacked males and were presumed to be parthenogenetic, but several independent origins of sexually reproducing taxa were found. Of the morphological characters, only the corpus shape was consistent with the molecular phylogeny, however, the utility of this character is also questioned. Many genera with complex probolae were also paraphyletic, including Nothacrobeles, Zeldia and Cervidellus, indicating the need for more comprehensive phylogenies and a broad taxonomic revision of the family.

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