Genetics of Postzygotic Isolation: The Extent of Genomic Coadaptation in Populations of a Microcrustacean

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0077940EdmandsHybridization between populations results in increased fitness (hybrid vigor) in some cases, and decreased fitness (outbreeding depression) in others. Outbreeding depression is a subject of concern for conservation and is also important to the study of speciation, because it marks the earliest stages of postzygotic isolation. The proposed work will explore the genetic basis of outbreeding depression using the copepod Tigriopus californicus. This species is well suited for such a study due to its short generation time, ease of husbandry and remarkable population structure, with reproductively compatible populations that range from genetically indistinguishable up to more than 20% divergent in mitochondrial DNA. Outbreeding depression is well documented in this species. The proposed study includes four objectives:1) To develop a linkage map, using a battery of molecular markers. Linkage group determination will be facilitated by the lack of recombination in T. californicus females.2) To find the sex-determining chromosome in T. californicus. This will be accomplished as a byproduct of the screening of markers in (1) and will allow tests of the role of sex chromosomes in speciation.3) To test fitness effects of whole chromosomes and interactions between chromosomes in a series of four crosses spanning a wide range of divergence. This will involve measuring associations between viability and genotype in backcrossed hybrids. Results will assess the extent of coadaptation across the entire genome and will reveal how conflicting gene interactions accumulate over time. 4) To demonstrate the fitness effects of interactions both within and between chromosomes and to test the expected pattern of stronger coadaptation between physically linked loci. Results will have significance for a number of different fields of biology. The data will contribute to basic evolutionary theory by measuring the magnitude of epistasis, a factor of increasing interest to evolutionary biologists. Results will be particularly relevant to the mechanics of reproductive isolation and will allow interesting comparisons to the large and elegant body of work on Drosophila. Finally, the proposed work will contribute to the field of conservation biology, which is becoming increasingly concerned over the consequences of interpopulation mixing. Because the nature and extent of coadapted gene complexes has implications for the duration of outbreeding depression, this research may be relevant to the design of management strategies.