Variation in courtship sounds among three geographical strains ofDrosophila mercatorum

Sound recordings of courtship inDrosophila mercatorum were analyzed with an oscilloscope. Sounds in this species consist of two kinds of pulses, referred to as the A and B sounds, respectively. These differ from each other in their oscilloscope pattern and in the behavior accompanying them. A comparative study of three strains from widely separated geographical regions (New York, El Salvador, and Hawaii) revealed significant differences among strains in the interpulse interval (ipi) of the A sound. The ipi of the B sound increased as it proceeded for New York and Hawaii males but not for males from El Salvador. These characteristics may influence mating success in interstrain corsses. The present results suggest that the first steps toward divergence in the nature of the sound are quantitative; this may affect the response threshold of the female. Genetic systems responsible for female receptivity may have been independently developed in the two sexes.This work was supported by research grants from the Ministry of Education of Japan (Nos. 034082, 312107), and was presented at the U. S.-Japan Seminar of Dynamics of Speciation in Plants and Animals, Tokyo, October 14–18, 1978.