Working Group Molecular Evolution and Phylogenetics

Molecular evolution of 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. However, most of our present knowledge 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. Amongst others, we found statistical evidence that changes in posttranslational modification might be promoted by positive Darwinian selection at the amino acid level. Other investigations revealed that the rate of sequence evolution of zonadhesin slows down in sexually more dimorphic and unimale breeding primate species such as the hamadryas baboon (P. hamadryas). The other extreme might represent the gray mouse lemur (M. murinus), which displays a weak inverse sexual dimorphism. Apparently, males in more sexually dimorphic species manage more successfully to monopolize access to estrous females, thus lowering the level of sperm competition, which in turn decreases the rate of sequence evolution of zonadhesin (see figure and publications).

Phylogeny of Gnathifera

The monophylum Gnathifera comprises several worm-like taxa, including free-living aquatic gnathostomulids and rotifers, epizoic seisonids and endoparasitic acanthocephalans ("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 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 epizoic lifecycle (see below figure). Moreover, the acanthocephalan subtaxon Palaeacanthocephala appeared paraphyletic in our analysis. However, this is only one hypothesis amongst others and the topic is still a matter of debate (see, e.g., Herlyn et al. 2003). The topic is apparently not in the focus of anthropology, but considering that acanthocephalans also use primates as hosts the connection becomes more evident…

Working group members

PD Dr. Holger Herlyn

Dr. Gomathi Gokulakannan

Julia Schuhmacher

Marie Beckhaus

Previously supervised candidates

(together with Prof. Dr. Hans Zischler)

Kerstin Dietrich (now Interdisziplinäres Zentrum für Klinische Forschung, University Leipzig)

Andreas Prothmann (now Institute of Molecular Genetics, Mainz)

Lena Lüke (now Reproductive Ecology and Biology Group, Museo Nacional de Ciencias Naturales, Madrid)