Lumbricus terrestris is an obligate outcrossing hermaphrodite and represents the largest earthworm in northern Europe. Infection of Lumbricus terrestris by Monocystis sp. is a well studied host-parasite system. Molecular markers are essential to understand the evolutionary dynamics of this relationship and to assess the importance of other processes such as mate choice and habitat fragmentation, historical processes (e.g. bottlenecks, range expansions), and direct and indirect selective forces that shape genetic variation in natural populations. Conducting such studies requires development of highly polymorphic molecular markers such as microsatellites. Therefore we constructed a microsatellite enriched genomic DNA library for Lumbricus terrestris and succeeded in having more polymorphic loci. Our primary use of these polymorphic microsatellites will be to study population structure and fertilization in a mate preference context in Lumbricus terrestris.

• Are certain host genotypes particularly resistant to certain parasite genotypes?
• Does a high level of population-wide genetic diversity enhance overall resistance?
• Is individual heterozygosity associated with resistance?
• Does mating behaviour influence the interaction with parasites?
• Reconstruct the recent mating history by analysis of stored allosperm.

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