Evaluation of the Ecdysozoa versus Articulata hypothesis on the basis of complete mitochondrial genome data
Final Report Abstract
In the course of working on mt genomics of the Ecdysozoa we sampled mt genomes from basal arthropod taxa, like onychophorans and tardigrades, thus filling some crucial data gaps. We have shown that the onychophorans are the sister group to the remaining euarthropods and the ecdysozoa are strongly supported. Data on Macrobiotus hufelandi, the only tardigrade mt genome, is not suitable to unravel the basal nodes of the arthropods, since at least this species is attracted by nematodes, chelicerates and pycnogonids. Contrarily, the gene rearrangement is highly conserved like in other arthropods and priapulids. To gain more reliable results concerning the position of the tardigrades more data need to be imposed. In this connection sequence information on M. hufelandi can serve as valuable template. The second mt genome of the priapulid species Halicryptus spinulosus is as conservative as the first published mt genome of Priapulus caudatus in terms of gene rearrangement and base composition. H. spinulosus shows the same inversion as P. caudatus and is supposed to occur in the lineage leading to priapulids. H. spinulosus forms together with P.caudatus a monophyletic clade, as expected, and priapulids are the sister group to arthropods (incl. Onychophora). Within the Arthropoda the phylogenetic position of Pycnogonida is not settled and support for a sister group relation to euchelicerates is only low. The results may be due to long-branch attraction artifacts and higher A+T content. However, we found no evidence for the Cormogonida hypothesis, a clade combining Pycnogonida as sister group to the remaining euarthropods. Decapod crustaceans constitute an extremely diverse taxon concerning mt genome rearrangements. We can show that an inversion in the marbled crayfish and Homarus gammarus is the same as the inversion in priapulids. Thus, we conclude that this inversion evolved convergently within the Ecdysozoa.
Publications
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(2006) The complete mitochondrial genome of the sea spider Nymphon gracile (Chelicerata: Pycnogonida). BMC Genomics 7: 284
Podsiadlowski L, Braband A
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(2007) The complete mitochondrial genome of Pseudocellus pearsei (Chelicerata: Ricinulei) and a comparison of arachnid mitochondrial gene orders. BMC Genomics 8: 386
Fahrein K, Talarico G, Braband A, Podsiadlowski L
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(2008) The complete mitochondrial genome of the onychophoran Epiperipatus biolleyi reveals a unique transfer RNA set and provides further support for Ecdysozoa hypothesis. Mol. Biol. Evol. 25: 42-51
Podsiadlowski L, Braband A, Mayer G
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(2009) Phylogeny and mitochondrial gene order variation in Lophotrochozoa in the light of new mitogenomic data from Nemertea. BMC Genomics 10: 364
Podsiadlowski L, Braband A, Struck TH, v. Döhren J, Bartolomaeus T
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(2010) Erosion of phylogenetic signal in tunicate mitochondrial genomes on different levels of analysis. Mol. Phylogenet. Evol.
Stach TG, Braband A , Podsiadlowski L
