Sperm displacement in the Drosophila bipectinata species complex: evidence for interspecific variations.

We studied sperm displacement in two members of the Drosophila bipectinata species complex i.e., Drosophila parabipectinata and Drosophila malerkotliana by employing mutant and wild type strains. We found a significant increase in the productivity of remated females than that of once mated ones in all the crosses of the two species. The P2' values range from 0.67 to 0.70 in D. malerkotliana and 0.52 to 0.56 in D. parabipectinata. These results were compared with that of our earlier finding in D. bipectinata belonging to the same complex. We found that though the three species exhibit differences in the degree of sperm displacement, the pattern is somewhat similar in the three species. However, as far as its genetic variability and population size maintenance is considered, D. malerkotliana and D. bipectinata (P2' is 0.60-0.67) are at the forefront. Our finding is also supported by the fact that D. parabipectinata is derived from D. bipectinata and has not diverged much since its emergence as a separate species. The differences in the pattern of sperm displacement may be attributed to differences in remating latency, duration of copulation in first mating and sperm usage pattern among the members of this complex.