Meerkat pups at Kuruman River Reserve, in South Africa's Kalahari Desert. (Credit: Christine Drea/Duke)
The pups of these female meerkat leaders pay a price for their mom's power, researchers report.
From silverback gorillas beating their chests to executives battling it out in the boardroom, the reputation for testosterone-fueled aggression and dominance has typically belonged to macho males.
But one group of animals flips the script. In meerkats, females are the fiercely competitive sex.
Members of the mongoose family found in the arid savannahs of southern Africa, most meerkat mobs have a dominant female at the head.
In meerkat society a dominant female is in charge. Growling, biting, pushing, and shoving to keep others in line, the meerkat queen wields absolute power over her subordinates, who have to help raise her pups.
The matriarch's bullying behavior is fueled by high levels of testosterone that can surge to twice those of her male counterparts when she's pregnant.
But while this chemical boost gives her a competitive edge and helps her keep the upper hand, it can also take a toll on the health of her offspring, says Duke professor of evolutionary biology Christine Drea, who coauthored the research with her then-graduate student Kendra Smyth-Kabay.
For the study, the researchers examined 195 meerkats as juveniles and adults at Kuruman River Reserve, in South Africa's Kalahari Desert.
The researchers checked the animals' droppings for tapeworm eggs and other signs of parasites. Comparing the pups of dominant and subordinate females, they found that the offspring of meerkat queens -- those exposed to higher levels of testosterone and related hormones in the womb -- tend to carry more gut parasites than other pups.
To find out if the moms' sky-high hormones during pregnancy were to blame, they also looked at a group of meerkat pups whose dominant mothers had received a medication during their third trimester that limits the effects of testosterone in the body.
Indeed, blocking a matriarch's testosterone improved the immune function of her pups. No longer bathed in testosterone in their mother's womb, these pups harbored fewer parasites and had stronger natural defenses against infection, based on blood tests of their body's ability to fight bacteria.
What's more, they were more likely to survive past their first year of life.
"The offspring from moms whose androgens were blocked actually survive significantly longer," Drea says.
The new study represents the first evidence in mammals that fetuses exposed to elevated testosterone in utero may have weakened immune function later on.
The negative link between prenatal testosterone and health was most pronounced in juveniles, disappearing by the time the pups reached adulthood.
"There's a health trade off with testosterone," Drea says. "It's actually having an effect on survivorship when the animals are the most vulnerable."
The work is part of a larger field aimed at understanding how animals fend off infections in the wild, beyond the controlled conditions of the lab.
"By studying wild meerkats, we can explore how real-world conditions -- factors like social status, hormones, and environmental stressors -- interact to influence immune function." Smyth-Kabay says.
The research appears in Ecology and Evolution.
Support for this research came from the National Science Foundation, the National Geographic Society, and the European Research Council.