Reported Drosophila courtship song rhythms are artifacts of data analysis
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RESEARCH ARTICLE
Open Access
Reported Drosophila courtship song rhythms are artifacts of data analysis David L Stern
Abstract 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. Keywords: Artifacts, Biological rhythms, Courtship song, Drosophila
Background Males of the vinegar fly, Drosophila melanogaster, flap one wing at a time to sing a courtship song to females [1,2] (Figure 1a). This song consists of trains of an approximately sinusoidal ‘sine song’ and a series of discrete pulses, called ‘pulse song’, often concatenated into song bouts [3] (Figure 1a). The time interval between individual pulses, called the inter-pulse interval (Figure 1a), tends toward a characteristic interval for each species of Drosophila that sings pulse song, and in D. melanogaster this inter-pulse interval is approximately 35 to 40 ms. However, the inter-pulse interval is variable at multiple time scales (Figure 1b,c): within a single train of pulses, between trains of pulses, between different individuals of a strain, and between different strains [3-5]. In 1980, Kyriacou and Hall [6] reported that, on average, the inter-pulse interval cycled with an amplitude of approximately 3 ms and a period of approximately 1 min (0.017 Hz) in D. melanogaster (Figure 1d) and 30 s (0.03 Hz) in D. simulans (Figure 1e). Following tradition, I will call this periodicity KH cycles. In the same paper, Correspondence: [email protected] Janelia Farm Research Campus, Ashburn, VA 20147, USA
they reported that mutations in the period locus that increased, decreased, and ablated periodicity of the circadian rhythm had similar effects on KH cycles. Later papers reported that transformation of the period locus into individuals carrying a null allele of the period gene restores KH cycles to arrhythmic males [7]; that females of D. melanogaster and D. simulans mate faster when presented with artificial so
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