Primates can alter the rate at which they reach sexual maturity. Previous studies have shown a variety of factors, including food availability, can determine whether primates mature earlier or later.

Now, for the first time, researchers have found that female geladas -- close relatives of baboons, found only in the Ethiopian Highlands -- accelerate their sexual maturity when new males take over.

Scientists shared the discovery in a paper published Thursday in the journal Current Biology.

"We found that prepubertal females are more likely to mature right after a new breeding male arrives in the group -- even if it means maturing earlier than expected," senior author Jacinta Beehner said in a news release.

"We also noticed that some of these maturing females were maturing much later than expected," said Beehner, a professor of psychology and anthropology at the University of Michigan.

According to the new research, later-blooming females were mostly the daughters of the primary breeding male prior to the turnover in leadership.

The pattern suggests female geladas can either accelerate or delay sexual maturity to avoid interbreeding with their fathers, researchers said.

"Once their father is ousted by the new male, they appear to lift this suppression and immediately mature," Beehner said. "Taken together, we see that a new male causes a really obvious increase in the number of maturations in a group -- whether early, on-time or late."

Normally, during any given year, the group of geladas being monitored by scientists featured only a handful of sexually mature females. But researchers began noticing that the arrival of a new male leader was often followed by the sudden sexual development of several females.

Researchers started monitoring the estrogen levels of females, which can be measured in feces, before and after changes in male leadership. Prior to sexual maturity, female primates start producing higher levels of estrogen.

"Females usually mature around 4.5 years old, but we saw that even females as young as one year old exhibited a temporary surge in estrogen," Beehner said. "We suspect that this boost in estrogen causes females to mature, but that some females are just too young for this boost to actually work."

The findings suggest the sexual maturity process in primates is both flexible and sensitive to social factors. While scientists have previously observed such characteristics among New World monkeys, the latest research marks the first time researchers have identified the phenomenon among Old World monkeys.

"If an Old World monkey, like geladas, can suppress maturation in response to the presence of their biological fathers and lift this suppression in response to the arrival of a novel male, it's possible that such a process could be present in apes, and possibly even in humans," Beehner said.

However, before gelatos are used to make inferences about the sexual maturity of primates, the researchers said more work needs to be done to understand what kinds of costs and benefits are associated with the acceleration or suppression of the maturation process.

"We have to be patient and wait until these females, now matured, live out their reproductive lives," Beehner said. "So, stay tuned, and we'll get back to you on that in another 14 years."

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Washington DC (UPI) Nov 2, 2019
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