9906531 Zeh Discoveries in molecular biology are providing growing evidence that the genomes of species are dynamic entities, constantly evolving, at least in part, as a result of genetic conflicts within and between the nucleus and the cytoplasm. Selfish genetic elements, such as cellular endosymbionts, transposable elements, segregation distorter alleles, maternal effect lethal alleles, as well as hyperavailable ("junk") DNA and imbalances in genomically- imprinted genes, can all undermine female fitness by rendering certain combinations of maternal and paternal genotypes incompatible within the developing embryo. The development of single-locus minisatellite DNA probes for the pseudoscorpion, Cordylochernes scorpioides, in combination with a mammalian-like viviparous reproductive biology highly amenable to experimentation and involving the production of large numbers of offspring, makes this species a model system for investigating the effects of paternal genotypes on female fitness. Through a research program involving behavioral analyses, breeding experiments and DNA profiling, this study will test the hypothesis that cellular and molecular interactions within the female reproductive tract can provide females with mechanisms for minimizing the risk and/or cost of fertilization by genetically- incompatible sperm. This genetic incompatibility hypothesis will be tested against several previously proposed hypotheses to explain how paternal genotypes can influence female reproductive success, namely the trading-up hypothesis, the inbreeding avoidance hypothesis and the intrinsic male quality hypothesis.