Sexual Isolation Between Drosophila melanogaster and Drosophila simulans

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Abstract
Single pair matings, using two strains of D. melanogaster (Oregon-R-C and e11) and a number of strains of D. simulans, have shown a considerably higher degree of sexual isolation than has been previously observed. Using young flies (less than 4 hours old) only 10 successful cross-fertilizations were obtained from 2,131 interspecific pairs, while aged flies (at least 3 days old) gave 40 successes out of 4,264 such pairs. With both young and aged flies, most of the successful cross-fertilizations were obtained for the D. simulans female x D. melanogaster male cross. In population cages, using D. melanogaster e11 and D. simulans p, only eight interspecific hybrids were found in a total of 167,762 flies examined. The higher degree of sexual isolation observed as compared with previous results, the generally more successful D. simulans female x D. melanogaster male cross, and the higher degree of sexual isolation in young as compared with aged flies are influenced by the effects of age on mating behavior, of male and female vigor, of sexual excitation, and of facilitation of mating in bottles containing more than one pair of flies.