The researchers reporting the work, Laura Beaver and Dr. Jaga Giebultowicz, found that male flies lacking one of two circadian clock genes, "period" or "timeless," exhibited an altered sexual behavior in which copulation time was significantly extended. Whereas copulation normally lasts for around 15 minutes, males carrying mutations in period or timeless spent up to 30-50% more time in copulation than their normal male counterparts. The effect is sex-specific, because mutant female flies copulating with normal males did not show a similar change in behavior.
Both the period and timeless genes are evolutionarily conserved components of the molecular circadian clock mechanism and are present in diverse species including humans. Both genes play critical roles in the control of the 24-hour clock. However, despite their roles in controlling the timing of daily behaviors such as sleep, the period and timeless genes appear to influence the duration of fly copulation through a mechanism that is separate from the daily circadian clock. The researchers found, for example, that altered oscillations of the circadian clock do not affect the flies' time in copulation and neither does constant light, which abolishes the clock function. Together, the new findings broaden the known set of behaviors controlled by the period and timeless genes and suggest that these genes might regulate biological processes within short as well as long time scales. Future studies should help elucidate the mechanism by which period and timeless control copulation--for example, by influencing male development or acting as components of a molecular timer.
Laura M. Beaver and Jadwiga M. Giebultowicz: "Regulation of Copulation Duration by period and timeless in Drosophila melanogaster"
Publishing in Current Biology, 24 August 2004, Volume 14, Issue 16, pages 1491-1497.