Abstract (eng)
The present study assesses the ability of the ribosomal gene encoding for the 28S rRNA to resolve
the position of myriapods inside the Euarthropoda as well as the earliest split events inside this
problematic group from phylogenetic point of view.
This study is based on 26 myriapod sequences from 22 taxa (6 newly sequenced) covering all
major subgroups of myriapods. Additionally, 16 representatives of Hexapoda, Crustacea, Chelicerata,
and as outgroup Milnesium tardigradum (Tardigrada), were used to gain more insight. Besides
the manual alignment strategy the present study investigates the reliability of a fully automated
alignment strategy (RNAsalsa) and alignment masking (ALISCORE). Tree reconstruction methods
encompass Maximum Parsimony, Maximum Likelihood, and Bayesian inference, as well as a tree
reconstruction method, which accounts for the dependence of base substitution in stem regions
of ribosomal genes (DNA/RNA mixed models) was conducted and implemented in a Bayesian
framework.
The results reveal high statistical support for a number of commonly accepted monophyletic
taxa, including Symphyla, Pauropoda, Chilopoda, Penicillata and Helminthomorpha, as well as
Euchelicerata, Pancrustacea and Hexapoda. The monophyly of Myriapoda is highly dependent on
the alignment strategy used to construct the data matrix. The monophyletic status of Diplopoda
is not supported under most data sets, but clearly divided into two subgroups (Helminthomorpha
and Penicillata). The position of myriapod subgroups inside the euarthropod tree remain instable
through all performed data sets and tree reconstruction methods. Even with the correction for
known problems in tree reconstruction, e.g. low taxon sampling, heterogeneity in base composition,
or violation of the assumed character independence, an optimization of the phylogenetic signal of
28S rRNA for the reconstruction of the phylogenetic position of all myriapod subgroups seems
hardly possible. An investigation of the secondary structure in myriapods could test whether the
lack of unambiguous resolution can be explained by a deviation from the "standard euarthropod
structure ".