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Various fitness components (fecundity, fertility, viability, developmental time, sex ratio, oviposition rhythm) have been studied in three sibling species, D. melanogaster, D. simulans, D. mauritiana, and three interspecific hybrids Mame, Masi and Masi-2, fertile for both sexes. The hybrid Mame originated from one D. mauritiana female crossed to a D. melanogaster male; Masi and Masi-2 resulted from different D. mawihhna females crossed to D. simulans males. Each species and hybrid was found to exhibit characteristic values for each fitness component. In many cases the hybrids did not exhibit intermediate values, compared with their parental species. The contribution of each fitness component to the speciation process, and the polygenic theory of reproductive isolation are discussed. The conclusion is that even the early speciation steps are accompanied by the same kind of genetic changes that have been described for species isolated for long periods. |
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