C.elegans /arthropod

Peter Schuchert schuchert at ubaclu.unibas.ch
Mon Dec 1 11:40:54 EST 1997

Pierre Pontarotti wrote:
> Hello I am loking for a reference showing that INSECT and Vertebrate
> are closer one to an other than they are with C.elegans

Things are not so easy as you may think, below some references 
(discussion on this subject is not closed yet)


McClintock-Turbeville J., Pfeifer D M., Field K. G., Raff R. A., (1991)
The phylogenetic status of Arthropods as inferred from 18S rRNA
sequences. - Mol. Biol. Evol. 8:669-681 

Aguinaldo-A-M-A, Turbeville-J-M, Linford-L-S, Rivera-M-C, Garey-J-R,
Raff-R-A, and Lake-J-A, (1997) Evidence for a clade of nematodes,
arthropods and other moulting animals. - Nature (London) 387(6632):
The arthropods constitute the most diverse animal group, but, despite
their rich fossil record and a century of study, their phylogenetic
relationships remain unclear. Taxa previously proposed to be sister
groups to the arthropods include Annelida, Onychophora, Tardigrada and
others, but hypotheses of phylogenetic relationships have been
conflicting. For example, onychophorans, like arthropods, moult
periodically, have an arthropod arrangement of haemocoel, and have been
related to arthropods in morphological and mitochondrial DNA sequence
analyses. Like annelids, they possess segmental nephridia and muscles
that are a combination of smooth and obliquely striated fibres. Our
phylogenetic analysis of 18S ribosomal DNA sequences indicates a close
relationship between arthropods, nematodes and all other moulting phyla.
The results suggest that ecdysis (moulting) arose once and support the
idea of a new clade, Ecdysozoa, containing moulting animals: arthropods,
tardigrades, onychophorans, nematodes, nematomorphs, kinorhynchs and
priapulids. No support is found for a clade of segmented animals, the
Articulata, uniting annelids with arthropods. The hypothesis that
nematodes are related to arthropods has important implications for
developmental genetic studies using as model systems the nematode
Caenorhabditis elegans and the arthropod Drosophila melanogaster, which
are generally held to be phylogenetically distant from each other.
Dr P. Schuchert
University of Bern
Dept. Clinical Research
Murtenstrasse 35
CH-3010 Bern Switzerland


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