Female geladas hurry up and mature when new male joins the group – study

A dominant gelada male and his group of females sitting on the edge of a cliff
A dominant gelada male and his group of females sitting on the edge of a cliff
16:00pm, Thu 05 Nov 2020
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Female primate relatives of baboons, known as geladas, suddenly hurry up and mature when a new male enters the picture, a new study has suggested.

Researchers say most mammals – including humans and other primates – reach sexual maturity early or late depending on lots of different factors, such as how much food there is to eat.

But, according to the scientists, they have shown for the first time that female geladas are more likely to mature when a new breeding male joins the group.

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

Senior author Jacinta Beehner, professor of psychology and anthropology at the University of Michigan, said: “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.

“We also noticed that some of these maturing females were maturing much later than expected.”

Many of those late bloomers were the daughters of the primary breeding male prior to the new male’s arrival, the researchers report.

Their observations suggest females can both speed up and slow down their maturity to avoid inbreeding with their fathers, according to the study published in the Current Biology journal.

Prof Beehner added: “Once their father is ousted by the new male, they appear to lift this suppression and immediately mature.

“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.”

The researchers kept track of the age at maturity for 80 females over 14 years of research in the highlands of Ethiopia – the only place where geladas are found in nature.

When the females mature they have conspicuous swellings surrounding a patch of skin on their chest and neck.

Researchers measured the females’ faeces for oestrogen, knowing that levels rise just before they visibly mature.

They found that oestrogen levels surged in immature females of all ages just after a new male took over.

According to the study, an oestrogen boost occurred even in females far too young to mature.

Prof Beehner said: “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 oestrogen.

“We suspect that this boost in oestrogen causes females to mature, but that some females are just too young for this boost to actually work.”

The findings suggest that maturation in many primates is a lot more sensitive to social environments than scientists had thought before.

The discovery may even have implications for humans, according to the researchers.

But they caution against taking the results in geladas too far in terms of what they might mean for humans since there are so many additional factors at play.

In future studies, the researchers hope to identify the costs and benefits associated with maturing early, on-time, or late for their gelada population.

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