ИСТИНА

SSU rDNA data has been used in universal phylogenetic studies to define major lineages within Nematoda and suggest a new scenario of their relationships. However, since first attempts to recover deeper nematode phylogenies it has become clear that conventional techniques of inference often do not suffice for this purpose. Intensive molecular phylogenetic analysis of the three major nematode clades demonstrated that relationships within Chromadoria are robustly inferred down to the deepest divergences. The deeper phylogenetic structure of Enoplia, on the contrary, is not robustly recovered even with the most sophisticated algorithms. A similar situation, albeit to a lesser extent, is characteristic of the Dorylaimia clade represented by only a few compact recent taxa. Our analyses suggest that the behaviour of the SSU rRNA gene is fundamentally similar in all nematode taxa. The main cause of bias in reconstructions of enoplian and dorylaimian phylogenies is a marked scarcity of reliable molecular characters to define deeper nodes of the tree, which is most likely to be due to poor taxon sampling. The current availability of evolutionary descendants of mile-stone divergences in Chromadoria permits the breaking of long inner branches of the tree and thus avoids computational artifacts caused, in particular, by disparities in rates of molecular evolution. A shortage of recent intermediate taxa in Enoplia appears to preclude similar solutions, and may result from their rapid initial radiation with subsequent extinction of greater number of descendant lineages. A similar evolutionary pattern is probably characteristic of Dorylaimia, although the amount of their recent taxa is very few. The latter allowes one to individually assess few competing phylogenies for reliability.