Abstract
In the nematode family Criconematidae, a taxonomy primarily based on cuticle characters has created classifications that are notoriously volatile. Molecular characters may lead to their stabilization. A phylogenetic tree of Criconematoidea was constructed using 166 new near full-length 18S rDNA sequences and 58 sequences from GenBank. Bayesian and maximum likelihood (ML) analyses produced trees with similar topologies. Major features include a strongly supported clade that includes Criconematidae and Hemicycliophoridae, excluding Paratylenchidae and Tylenchulidae. Another well-supported clade groups Criconema, Ogma, Crossonema, and Hemicriconemoides plus Xenocriconemella, combining nematodes with cuticular scales with those without scales at any life stage. Mesocriconema, Discocriconemella limitanea, Hemicaloosia, and Lobocriconema are recognized as monophyletic groups, but Criconemoides is paraphyletic. Both trees support an unexpected sister relationship between Bakernema and Hemicycliophora. The 18S rDNA dataset was insufficient for distinguishing genus boundaries between Criconema, Ogma, and Crossonema. The relationships depicted by the 18S rDNA phylogeny suggest that key morphological characters used in the classification of Criconematidae are not homologous.
Highlights
In the nematode family Criconematidae, a taxonomy primarily based on cuticle characters has created classifications that are notoriously volatile
In the introduction to Geraert’s (2010) The Criconematidae of the World – Identification of the Family Criconematidae (Nematoda), he states that ‘‘there is a chaotic situation in the taxonomy of the Criconematidae.’’ This immensely useful resource was an effort to assemble descriptions of all of the recognized species of Criconematidae
Consistent strong support is found in the deepest node (A) that excludes the two Paratylenchus Micoletzky, 1922 groups, Tylenchulus Cobb, 1913, and Tylenchocriconema Raski and Siddiqui, 1975, but includes the family Criconematidae Taylor, 1936 and all the Hemicycliophora specimens in the dataset
Summary
In the nematode family Criconematidae, a taxonomy primarily based on cuticle characters has created classifications that are notoriously volatile. Mesocriconema, Discocriconemella limitanea, Hemicaloosia, and Lobocriconema are recognized as monophyletic groups, but Criconemoides is paraphyletic Both trees support an unexpected sister relationship between Bakernema and Hemicycliophora. The validity of phylogenetic groupings within Criconematina was addressed by Subbotin et al (2005) using the D2/D3 region of 28S rDNA The results of their analyses highlighted several taxonomic questions such as the distant relationship of Mesocriconema sphaerocephalum (Taylor, 1936) Loof and De Grisse, 1989 to other species of Mesocriconema Andrassy, 1965 and the relatively distant relationship between the two sheath-forming genera, Hemicriconemoides Chitwood and Birchfield, 1957 and Hemicycliophora de Man, 1921, but otherwise found little ‘‘resolution of relationships between main lineages’’ (Subbotin et al, 2005). Taxonomic implications and recommendations for future research are drawn from 18S rDNA and cytochrome oxidase subunit I(COI) DNA sequences
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