TABLE CONTENTS

Phylogeny and Evolution of Rhabditid Nematodes
Kiontke, K. & D. Fitch
Department of Biology, New York University, New York, NY 10003, USA
A new, multigene molecular phylogeny resolves most relationships among major groups of
rhabditid nematodes and provides a framework for studying character evolution. In this
phylogeny, rhabditids are paraphyletic with regard to Strongylida and diplogastrids. The first
branch is Poikilolaimus and there are three major clades: (1) ‘Eurhabditis’, which includes
Caenorhabditis and its sister ‘Protorhabditis group’ (which includes Diploscapter), the
‘Rhabditis group’ (including Oscheius, strongylids, Heterorhabditis, and other clades) and
Choriorhabditis; (2) Rhabditoides inermis + diplogastrids; and (3) ‘Pleiorhabditis’, which
includes Rhabditoides inermiformis, Rhabditoides regina, Pelodera, and the ‘Mesorhabditis
group’ (which includes Parasitorhabditis). The phylogeny reveals that many characters have
evolved convergently; e.g., reproductive mode, intron positions, developmental characters,
and parts of male tail morphology. However, a number of morphological and developmental
characters demonstrate high consistency with the molecular phylogeny, providing additional
support for several clades. For example, a slit-shaped vulva is apomorphic for ‘Eurhabditis’;
the orientation of a cell division in the 2-cell embryo flipped 90˚ in the ancestor to the
Protorhabditis group; species in the Mesorhabditis group share a posterior vulva and
prodelphy; and a pharynx lacking a median bulb is derived and evolved only once in
rhabditids. Several previously defined taxa correspond with monophyletic groups (e.g.,
Oscheius, Caenorhabditis, Pelodera, and Poikilolaimus sensu Sudhaus) or paraphyletic
groups (e.g. Protorhabditis with respect to Diploscapter and Prodontorhabditis). Some other
taxa are polyphyletic (e.g. Pellioditis, Rhabditis, and Rhabditoides). To support systematic
research and studies in comparative biology and character evolution, we continue to build a
representative living collection of rhabditid species (currently ~140). Current efforts are
focused on finer phylogenetic resolution. Future goals are to develop a classification system,
an electronic key, and a systematics database for rhabditids.
Turning Trees into Taxonomies
Adams, B.J.
Department of Microbiology & Molecular Biology, and Evolutionary Ecology Laboratories, Brigham Young
University, Provo, UT.
What began with Plato and Aristotle (and arguably much earlier) and was ultimately
canonized by Linné, culminated in a conflict that continues to this day, namely, what is the
best way to classify life on earth? Ever since Darwin, the idea that all species can be depicted
in a hierarchical tree of successively more inclusive groups has been a driving force behind
the movement to produce taxonomies that are consistent with evolutionary history
(phylogeny). Few quibble against the utility of such taxonomy. However, arguments over
the best way to accomplish this goal have been most acrimonious. Key to the proposed
solutions is the philosophical questions of whether natural groups exist independent of human
observation, and how they should best be reflected in taxonomic systems. I discuss
competing approaches in a historical context, and provide examples to demonstrate that
Linné’s 273 year-old system, with some modification, is sufficient to accommodate
monophyletic classification.
5 th International Congress of Nematology, 2008 19