Regularity versus irregularity in specific songs of closely-related drosophilid flies

The songs of most insect species are stereotyped and show regular rhythms which can be readily defined and described. In such cases, closely related species produce songs which differ in rhythmic structure, carrier frequency, or combinations of these parameters. We have examined the songs produced during courtship of the sibling drosophilid fly species Zaprionus tuberculatus, Z. sepsoides and Z. mascariensis which are known from morphometric and chromosomal evidence to be closely related. Drosophilid songs are produced by wing beating and normally consist of a regular series of similar mono- or polycyclic sound pulses with carrier frequencies of 150 to 500 Hz and pulse periods of 8 to 250 ms (for review, see ref. 9). Some species produce more than one type of song, and the pulsed song may be interrupted by protracted bursts of constant frequency tone.