Aging neutralizes sex differences in the brain: Study

Fruit flies' brains become desexualized as they get older, both male and female. Both sexes experience age-related changes, but the male brain becomes more feminized to a larger extent than the female brain becomes masculine. A study conducted by a research team at Linkoping University came to this conclusion.

The research is published in the journal - Proceedings of the Royal Society of London B.

Weaker individuals cannot afford to "invest" in sexual behaviors to the same degree as their healthier conspecifics, which is a well-known fact. It is unclear, though, whether aging, which weakens people, also causes a decrease in interest in sexual activities. Going "all in" on reproduction might seem like the best option for people who are nearing the end of their lives in order to pass on their genes before it's too late. The brain controls sexual behavior, so researchers looked at how the expression of specific genes changes with age in young males and females to learn what happens to sex differences in this tissue in fruit flies.

According to Dr. Antonino Malacrin, one of the study's primary authors who is currently employed at the University of Reggio Calabria in Italy, "our results demonstrate that gene expression in male and female brains becomes more similar with age and that both sexes contribute to this pattern."

The study demonstrates that a gene's expression is reduced in older females and increased in old males if the gene's expression is higher in the brains of young females than in young males, and vice versa for genes with higher expression in young males.

According to Antonino Malacrin, "The results also demonstrate that the changes are more pronounced in males than in females."

Since there is presumably a weaker correlation between investment in sexual traits and reproductive success in females than in males, females age more slowly than males do. A female fruit fly only needs to choose how much energy she has available for reproduction, whereas a male fruit fly must outcompete other males in quickly finding females and persuading them to mate through a challenging dance performance. Age implies that there are fewer resources available for both sexes to invest in reproduction and other activities, but males face greater costs of increased investment due to male-to-male competition.

Senior associate professor at the Department of Physics, Chemistry, and Biology (IFM) at Linkoping University and the study's principal investigator, Urban Friberg, claims that if you continue to expend as much energy on reproduction as you did when you were younger, you won't have any leftover for survival.

Studies on other animals, including humans, that have mainly focused on age-related changes in one sex's gene expression have produced results that point in the same direction. This suggests that many other animals may experience the same outcomes as fruit flies.

Even though the two populations of fruit flies that have been studied differ significantly in terms of the genes involved, Urban Friberg notes that the general results are the same in both of them.

The study's findings are similar to those the team discovered in a prior investigation. In that study, male and female flies with high and low genetic quality were compared for sex differences in gene expression. The earlier study demonstrated that decreased genetic quality causes gene expression in male and female flies to be more similar, much like how aging reduces sex differences. Once again, males changed their gene expression more than females.

The study does not address what molecular signal connected to aging is responsible for the diminished sex differences in the brain. If the signaling molecule turns out to be shared by other species, further research on this subject may prove fruitful.