The study was just published by scientists from Oregon State University in a professional journal, Current Biology, and reports a surprising new role for these clock-related genes. Mutations in the clock genes "period" and "timeless" caused male flies to copulate significantly longer than usual.

This shows that clock genes affect not only behaviors on the time scale of 24 hours, but also behavioral timing on the order of minutes, including the length of the sex act. It also indicates that genes which were thought to be dedicated clock components seem to have a wide range of other effects that may have nothing to do with cyclic patterns of day and night.

"These genes probably have important regulatory functions in many other areas that we do not yet understand," said Jaga Giebultowicz, an OSU associate professor of zoology and principal investigator on this study.

For instance, Giebultowicz's team has found recently that when these genes are missing, both male and female fruit flies produce less sperm and eggs, and are less fertile.

In the course of this research on fecundity, a graduate student in Giebultowicz's lab, Laura Beaver, was observing flies in mating chambers, and noticed that flies missing normal period or timeless genes tended to copulate 30-50 percent longer than usual. In more detailed research, it was learned that it was the male fly that determined how long to continue the mating process and was prolonging the event – he decided when it was time to quit, and that decision clearly involved clock genes.

In other studies over many years, the gene period, as well as other "clock" genes, have been extensively explored.

Giebultowicz has found, for instance, that constant exposure to light can "switch off" the biological clock in the male gypsy moth and cause them to become sterile.

However, when it comes to mating behavior in fruit flies, light was not an issue. There was no change in the response in flies exposed to constant light. This demonstrates that "period" and "timeless" regulate mating behavior in a novel way unrelated to the clock. These genes control not only when certain behavioral acts may occur, but also how long they may last.

Clock genes are also found in humans – they have been conserved between tiny fruit flies and humans through millions of years of separate evolution. In humans, they affect a vast array of functions from sleep to body temperature, the nervous and hormonal systems, moods and work productivity.

Clock genes also regulate time perception in humans, a process that may be somehow related to measuring time elapsed in the act of mating by flies, Giebultowicz said. To understand how clock genes are involved in regulating the length of behavioral acts and short-term time perception will require further study, she said.