molecular evolution, phylogenetic systematics, primatology, parasitology
Molecular genetics of the sperm-egg interaction
Recent studies on sequences coding for proteins of the sperm-egg interaction revealed high substitution rates combined with a high proportion of amino acid altering to amino acid preserving substitutions. Most of our present knowledge, however, is restricted to externally fertilizing organisms such as echinoderms and molluscs. To broaden our knowledge on internally fertilizing species, we analyze the evolution of proteins like the mammalian sperm-ligand zonadhesin that binds postacrosomally to the zona pellucida (see figure). Amongst others, we found statistical evidence that changes in posttranslational modification might be promoted by positive selection at the amino acid level (see publications).
modifed after Figure 2 in www.fz-juelich.de/ ibi/ibi-1/Sperm_Physiology/
Phylogeny of the Gnathifera
The monophylum Gnathifera comprises several worm-like taxa, including the free-living aquatic Gnathostomulida and "Rotifera", the epizoical genus Seison and the endoparasitic Acanthocephala ("thorny-headed worms"; for an example see figure: male of Paratenuisentis ambiguus). The juvenile stages of the latter mature in the body cavities of insects, myriapods and crustaceans (intermediate host), while the adults reproduce in the intestinal tract of vertebrates (definitive host). The different life cycles within the Gnathifera pose the question of how the acanthocephalan endoparasitism evolved from free-living ancestors.
Based on 18S rDNA data we found evidence supporting an earlier hypothesis whereafter the endoparasitism of acanthocephalans evolved from free-living ancestors via an epizoical lifecycle as shown today by Seison (see figure). Moreover, the acanthocephalan subtaxon Palaeacanthocephala appeared paraphyletic in our analysis. However, this is only one hypothesis about the phylogeny of Syndermata and Acanthocephala, respectively, and the topic is still matter of debate (see, e.g., Herlyn et al. 2003).
modified after Herlyn et al. (2003; see publications)
Links Holger Herlyn
