Cornell study uncovers 'jet lag' with female fruit flies that mate

The phenomenon of mating causing "jet lag" in female fruit flies and changes in their behavior, first reported by Cornell University researchers, comes down to how the female flies usually go about their days and how that changes when they encounter a male, one of the researchers said.

The researchers at Cornell's Wolfner Lab found that the seminal fluid protein a male fruit fly transfers to a female changes gene expression related to her circadian clock, according to Cornell's Jan. 30 news release.

Without the encounter, the female fly's day would have been very different, said Mariana Wolfner, Cornell professor of molecular biology and genetics and one of the research paper's senior authors, in the news release.

"Flies like to eat at certain times of day," Wolfner said. They sleep at certain times, and the circadian clock machinery controls when flies are likely to do these things. What we're seeing is that these very same behaviors, such as sleeping and eating, are changed after mating by the sex peptide. One way it might do that is by basically shifting the whole clock of the fly."

Behavioral changes researchers noted in mated female Drosophila, commonly known as fruit flies, included increased egg laying, aggression and other activities such as feeding. They also noted reducing sleep and interest in mating among previously unmated females.

The technique researches used involved removing the heads of female fruit flies during 10 time points in the first 24 hours after mating, with an eye toward discovering which genes are implicated post-mating and how long it takes a male's sex peptide to cause changes in a female. 

The "surprising findings" came after researchers examined transcriptomes, RNA sequencing that reveals gene expression, which genes are turned on and off, at different times while providing high-resolution data illuminating order in which that changes occurs, the news release said. 

The RNA sequencing was done in the lab of Andrew Clark, the Jacob Gould Schurman Professor of Population Genetics in Cornell's College of Arts and Sciences, and the study's senior and corresponding author.

Researchers used three treatments as part of the study on female flies that had grown up together. One of the treatments was an unmated control while another involved females who were mated with "a standard male" and a third were females "with a male that did not produce sex peptide," the news release said.

Within four hours of mating, the researchers found changes in gene expression of female flies' metabolism and the circadian clock. Researchers don't know what triggered initial changes but said pheromones or seminal fluid proteins other than sex peptide are possible candidates. 

Researchers also found the initial effects were short lived, that they didn't last without the sex peptide "and seemed to prime the system," the news release said.

Later, in the second phase, researchers noted sex peptides caused changes to genes regulating circadian rhythms and also genes that themselves are regulated by a fly's circadian clock pathways.

The findings were published Jan. 27 in the Proceedings of the National Academy of Sciences.