Developmental variations among Panagrolaimid nematodes indicate developmental system drift within a small taxonomic unit
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Comparative studies of nematode embryogenesis among different clades revealed considerable variations. However, to what extent developmental differences exist between closely related species has mostly remained nebulous. Here, we explore the correlation between phylogenetic neighborhood and developmental variation in a restricted and morphologically particularly uniform taxonomic group (Panagrolaimidae) to determine to what extent (1) morphological and developmental characters go along with molecular data and thus can serve as diagnostic tools for the definition of kinship and (2) developmental system drift (DSD; modifications of developmental patterns without corresponding morphological changes) can be found within a small taxonomic unit. Our molecular approaches firmly support subdivision of Panagrolaimid nematodes into two monophyletic groups. These can be discriminated by distinct peculiarities in early embryonic cell lineages and a mirror-image expression pattern of the gene skn-1. This suggests major changes in the logic of cell specification and the action of DSD in the studied representatives of the two neighboring nematode taxa.
KeywordsNematoda Molecular phylogeny Cell lineage In situ hybridization skn-1 Developmental system drift
P.H.S. was funded by a personal grant of the Volkswagen Foundation in the framework of the Initiative for Evolutionary Biology and by the German Research Foundation (DFG) through the grant SFB680 to T. Wiehe, Institute for Genetics, University of Cologne.
C. L. was funded through a Fletcher Jones endowment and a USD International Opportunity Grant. The authors are grateful to Walter Traunspurger for sharing the Propanagrolaimus strain WTM1. C.L. thanks Terry Bird, Keith MacDonald, and the Biology 342 Microbiology lab students (USD) that first found LC91 in Winogradsky columns made from the San Diego River mud.
The authors declare that they have no competing interests.
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