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Researchers at Brookfield, Lincoln Park Zoos confirm menopause in gorillas

By William Mullen
Tribune staff reporter
Published February 12, 2006

<x-tad-bigger> Alpha, a 45-year-old lowland gorilla at Brookfield Zoo, would be roughly 70 in human terms, but she continues to display such a robust libido that two worried zoo scientists launched a study four years ago to see if she could still become pregnant.

To put it another way, they wanted to know: Do gorillas go through menopause?

While human females often live a third of their lives beyond their child-bearing years, science had thought that all other species are able to reproduce until they die. But the researchers at Brookfield Zoo and Lincoln Park Zoo have found otherwise in a study being published in the International Journal of Primatology.

Their discovery that some older gorillas are menopausal has implications for zoos, which, for example, could take some apes off birth control without fear of a risky pregnancy. The researchers also hope the information may help unlock mysteries of human menopause, including how it evolved.

Proving that the rigors of scientific inquiry are not always glamorous, the study required cooperating ape keepers from zoos all over the country to meticulously collect droppings from certain gorilla females. They put green food coloring in the apes' snacks to produce easily identifiable green droppings, which keepers put on dry ice and shipped by overnight mail to Chicago to be analyzed for a key hormone.

Alpha, the gorilla who inspired this undertaking, is a mother of seven whose last baby was born in 1991. She continues to go into heat every month, which means that for two days she vamps for Brookfield's male gorilla leader, Ramar.

"It's not uncommon for female gorillas to strut about, purse their lips and throw glances at the male to let him know they are in estrus and would be receptive to his attentions," said Sylvia Atsalis, a staff primatologist at Brookfield. "But Alpha is particularly unabashed in this regard."

Because Ramar seems most interested in younger females, her attempts often fail, perhaps leading her to try harder. She sits close to him and stares into his eyes. She throws hay in his face. She tries sitting in his lap and makes lewd gestures.

"I've seen them mate, but it is very rare and it is half-hearted on Ramar's part," Atsalis said. "Usually he just ignores her, and sometimes he gets so aggravated that he chases her away."

Nonetheless, four years ago Atsalis and a colleague became concerned that Alpha could be impregnated in one of her successful encounters. Gorillas are considered geriatric at 30, and they worried that at Alpha's age a delivery would be risky for her. Having her on birth control also was risky.

"There are certain contraindications that can occur from birth control medicine, like the possible increased cancer risks and heart disease," said Susan Margulis, then a behavioral researcher for Brookfield.

Margulis, who moved to Lincoln Park Zoo in 2004 to become its primate curator, and Atsalis guessed that Alpha could not become pregnant, because only a handful of female gorillas older than 37 have had babies. But guessing wasn't good enough, so they set out to determine if Alpha had gone through the change of life.

One of the mysteries of human aging is that the reproductive system ages faster than other physical systems in women's bodies, so their ability to reproduce ends long before the end of their life span. In human males, the reproductive system declines with age but usually does not shut down until death.

A human female, Atsalis said, is defined as menopausal when she experiences "complete cessation of her menstrual cycle for a year. Then she is considered post-menopausal."

Menstrual cycles are not as obvious in apes as they are in humans, but Atsalis and Margulis suspected that gorilla females, if they lived long enough, would experience menopause and perimenopause, a prior stage of irregular cycling.

Their initial experiment involved tracking Alpha's daily levels of the reproductive hormone progestogen by testing her fecal droppings. They also tracked two other females in Alpha's group--one younger and fertile, and the other Alpha's age but ailing physically, an animal who had shown no overt interest in mating for years.

Study gains momentum

The results so intrigued the National Institute on Aging, the primary federal funding agency for research on human aging, that it awarded Atsalis and Margulis a grant for a bigger study of 30 female gorillas in 17 zoos.

Those apes ranged in age from 11 to 52, though 20 of them were 35 or older. The 52-year-old, Jenny, the oldest known gorilla in the world, lives in the Dallas Zoo. Also included was the second oldest, Colo, the first gorilla born in captivity, in 1956 in the Columbus Zoo in Ohio.

The precious green cargo sent by the participating gorilla keepers went to Brookfield's endocrinology lab, overseen by Nadja Wielebnowski, an ecologist and Brookfield's vice president of conservation science.</x-tad-bigger>

<x-tad-bigger>In the last two decades, zoos have been hiring scientists from a broad spectrum of disciplines to do increasingly sophisticated research in the quest of improving animal care. Wielebnowski fits that mold, as do Atsalis, a biological anthropologist, and Margulis, an evolutionary biologist.

The national study results confirmed that some older gorilla females have gone through menopause. It also suggests that they experience perimenopause, a stage in human females during which reproductive cycles become more erratic as menopause approaches.

At Brookfield, the hormonal studies showed the infertile older ape to be postmenopausal, confirmed the fertility of the younger female and indicated that Alpha is perimenopausal. Though her estrus cycle is regular, the rest of her cycle is so irregular that she can no longer conceive.

Primatologist Joe Erwin agrees.

"There have been some people who for some time argued that menopause is a uniquely human characteristic that does not occur in any other animal," said Erwin, executive director of the Foundation for Comparative and Conservation Biology. Based in Washington, D.C., the non-profit agency promotes primate research, particularly when it can be related to the study of human health issues.

Erwin, who 20 years ago was Brookfield's primate curator, said the study results of Atsalis and Margulis confirmed what he had long thought.

Similarities with humans

"Primates do have reproductive cycles similar to what humans have," he said. "Remarkably in great apes and Old World monkeys, it is very similar in terms of physiology, endocrinology and timing to humans, so it's not so surprising to see they experience menopause."

Wild gorillas rarely live as long as 35 years, he said. Few captive gorillas used to live that long, either, but in the last 30 years so much has been learned about their medical, nutritional and social needs that zoo apes are living deep into their 40s. In other words, captive female apes are now living long enough for menopause to show up.

The great apes--gorillas, orangutans and especially chimpanzees and bonobos--genetically are so similar to humans that scientists feel studying the apes may be the key to understanding the underlying evolution of many human medical issues and behaviors.

Interest in the health issues of menopausal women is increasing among scientists and health-care providers because by 2025 the projected global population of women 65 years old or older is 825 million. Studying menopause in other great apes, Erwin said, may tell science why menopause evolved in primates and how to combat its associated health problems, like osteoporosis and heart disease.

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wmullen AT tribune.com

sent by Natasha Matza
www.primatesanctuary.org
www.primatesanctuary.blogspot.com</x-tad-bigger>