Reported Drosophila courtship song rhythms are artifacts of data analysis

Background: In a series of landmark papers, Kyriacou, Hall, and colleagues reported that the average inter-pulse interval of Drosophila melanogaster male courtship song varies rhythmically (KH cycles), that the period gene controls this rhythm, and that evolution of the period gene determines species differences in the rhythm's frequency. Several groups failed to recover KH cycles, but this may have resulted from differences in recording chamber size. Results: Here, using recording chambers of the same dimensions as used by Kyriacou and Hall, I found no compelling evidence for KH cycles at any frequency. By replicating the data analysis procedures employed by Kyriacou and Hall, I found that two factors - data binned into 10-second intervals and short recordings -imposed non-significant periodicity in the frequency range reported for KH cycles. Randomized data showed similar patterns. Conclusions: All of the results related to KH cycles are likely to be artifacts of binning data from short songs. Reported genotypic differences in KH cycles cannot be explained by this artifact and may have resulted from the use of small sample sizes and/or from the exclusion of samples that did not exhibit song rhythms.