Molecular basis of reproductive isolation in blue mussels (Myrtilus, Bivalvia): Identification and characterization of gamete-specific factors

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Free spawning sessile marine invertebrates are an excellent model system to study molecular mechanisms underlying reproductive isolation. This is because the process of species recognition (pre-zygotic isolation mechanism) is almost entirely restricted to the process of gamete interaction in these organisms. A well suited example to study gamete interaction in sessile marine invertebrates is the Mytilus edulis species complex (M. edulis, M. trossulus, and M. galloprovincialis) because allopatric populations exist worldwide which hybridise in zones of interspecies contact. Previous studies mainly focussed on the molecular evolution of a single gene encoding the acrosomal protein M7 lysin. The project outlined here aims at searching for a broad range of candidate factors involved in gamete interaction occurring in all cellular compartments of sperm and eggs. Selective antibody production will be used to identify new factors and the antibodies will be used for initial functional characterization of these molecules. A strong focus will lie on finding relevant proteins and their corresponding genes. Selected proteins will be comparatively analysed to investigate patterns of their molecular evolution by looking at allopatric Mytilus populations. Furthermore, factors found in this study will be functionally characterized in respect to their role in reproductive isolation based on two approaches: i) insemination assays, and ii) analysis of species specific allele frequencies in the Baltic M. edulis – M. trossulus contact zone. The ultimate goal of the project is an understanding of function and evolution of reproductive isolation under the conditions of external gamete interaction/fertilization in a marine invertebrate.