Genetic basis of sperm and testis length differences and epistatic effect on hybrid inviability and sperm motility between Drosophila simulans and D. sechellia.

摘要

Results are reported from a genetic study of hybrid inviability and 3 'fertilization traits' (sperm motility and length, and testis size) that affect hybrid sterility between the sibling species D. simulans and D. sechellia. The main findings were as follows: (i) For sperm length there was a dominant effect of the D. simulans genome over that of D. sechellia, and the Y chromosome of D. sechellia in the background of D. simulans reduced the sperm length; (ii) In contrast, testis length, in spite ofits generally high correlation with sperm length, showed an additive effect; (iii) A strong asymmetric incompatibility between the D. sechellia X chromosome and D. simulans autosomes was found: D. sechellia X chromosome with D. simulans autosomes, but not the reverse, showed a significant reduction in testis length as well as in hybrid inviability compared to the parental species; (iv) Between the two autosomes, chromosome 3 had a greater effect on these traits than chromosome 2, and there was additionally an epistatic effect between these chromosomes with respect to their parental vs. recombinant status: recombinant chromosomes 2 and 3, together, had lower viability than any other combination; (v) The testis size in the backcross generation was greater than the parental species, suggesting that some modifier genes are being released from their species-specific genetic control; (vi) The species-specific homogeneity of the genome was important for all 3 traits - offspring viability, hybrid male fertility and testis length. These results are discussed with respect to the role of sexual selection and genetic divergence during speciation.