Lomb-Scargle periodogram analysis of inter-pulse interval time series. (a) Lomb-Scargle periodogram of a single 45-min time series from a Canton-S male. Power at frequencies ranging from approximately 0.0001 to 2 Hz is shown. Horizontal lines representing significance values at alpha equal to 0.1, 0.05, 0.01, and 0.001 are shown and labeled. This recording displayed numerous peaks significant at alpha <0.01 in the range of approximately 0.1 to 1 Hz and one peak significant at this level at approximately 0.03 Hz. The high-frequency peaks represent modulations in the inter-pulse interval on the order of seconds, which are observed often in male courtship song (compare with Figure 1b). (b-f) Summary of Lomb-Scargle periodogram results over all recordings of D. melanogaster Canton-S males. (b) The P-values for all peaks in the Lomb-Scargle periodograms significant at the 0.01 level and below. (c-f) The P-values of only the single strongest peak from the Lomb-Scargle periodogram of each recording (c), for songs binned into 10 s intervals (d), for the first 5 min of song binned into 10 s intervals (e), and for songs divided into 5 min recordings and binned into 10 s intervals (f). In all panels, frequency, in Hz, is displayed along the X axis. The vertical color bars represent the range of KH cycles for D. melanogaster from the 1980 publication (blue), for all D. melanogaster and D. simulans published values from 1980 to 1991 (red), and for all genotypes from 1980 to 1991 (grey), respectively (compare with Figure 2b).