Haldane's Rule and the Genetic Basis of Hybrid Male Sterility in Drosophila Simulans, Drosophila Mauritiana and Drosophila Sechellia

Abstract

<p>Genetic analysis of hybrid sterility and inviability has recently become a successful experimental approach to pursue the problem of speciation. In the present study, classical genetic analyses and high resolution two-dimensional gel electrophoresis (2DE) have been used to investigate the genetic basis of hybrid male sterility in three sibling species of the Drosophila melanogaster species subgroup. The genetic basis of Haldane's rule, i.e., the preferential hybrid sterility and inviability of heterogametic sex, is also examined. The D. sechellia Y chromosome was shown to have no effect when placed in the background of D. simulans. This shows that the X-Y interaction hypothesis can not be a general explanation of Haldane's rule. Cytoplasmic factors were shown to have no effect on hybrid male sterility between D. simulans and D. mauritiana and between D. simulans and D. sechellia. An asymmetric X-autosome interaction provides the best explanation of hybrid male sterility between D. simulans and D. sechellia. The asymmetric model of X-autosome interaction can also explain the asymmetries (unidirectionality) in reproductive isolation commonly observed between related species.</p> <p>Testis protein divergence on X chromosome was shown to be smaller than that on autosomes between these species. This implies that Haldane's rule may not be accounted for by a faster evolution of the X chromosome. The number of genes involved in hybrid male sterility between D. simulans and D. sechellia was shown to be small by using 2DE. A few D. sechellia specific testis proteins were identified to be consistently associated with male sterility.</p> <p>A general method for detecting major hybrid male sterility genes has been introduced. By using this method, a single Mendelian factor of D. mauritiana which produces complete male sterility in the background of D. simulans was identified and mapped to the X chromosome.</p>