Drosophila courtship song cycles in normal and period mutant males revisited.

Courtship songs of normal males and those expressing short-period, long-period, and arrhythmic mutations at the period (per) locus of Drosophila melanogaster have been reanalyzed for rhythmic components, using spectral treatments of the fluctuating rates of tone pulse production that occur during courtship. It was concluded, as in previous studies, that such songs are strongly rhythmic, except for courtships performed by per01 males. Songs produced by males expressing this and other per alleles were compared to computer-generated "random" ones. Interpulse interval variations influenced by per01 and songs stimulated to be arrhythmic both were found to be associated with cryptic rhythmicities; several such period values, extracted by the spectral analyses, defined very short cycle durations. We discuss the implications of these findings and of some recently reported results that have challenged the existence of rhythmicity in Drosophila songs.