Lemur females behave more like the males thanks to a little testosterone, says a group of biologists at Duke University in Durham, NC.
Male and female black lemurs (Eulemur macaco). Image credit: Brocken Inaglory / CC-BY-SA-3.0.
In most mammals, males are more aggressive and, in hierarchical societies, often dominate females. But in lemures, female social dominance over males is the norm.
It’s not uncommon for lemur females to bite their mates, snatch a piece of fruit from their hands, whack them in the head or shove them out of prime sleeping spots. They mark their territories with distinctive scents just as often as the males do. Males often don’t take their share of a meal until the females have had their fill.
“If a male lemur is enjoying a patch of sunlight, for example, a female is likely to push him aside and take his spot,” said Joseph Petty, a doctoral student at the Duke University’s Department of Evolutionary Anthropology.
Most female mammals that get their way over males are well-armed to be the bullies. Dominant female spotted hyenas, for example, are bigger and heavier than males. But female dominance in lemurs remains a puzzle.
Female lemurs are no bigger than males, and they don’t have antlers or bigger fangs to give them a physical edge over their mates.
Petty and his colleague, Prof Christine Drea, said that females have significantly lower testosterone levels than the males across the board.
But when they compared six lemur species – Eulemur rubriventer, E. macaco flavifrons, E. coronatus, E. mongoz, E. fulvus collaris, and E. f. rufus, they found that females of some species have higher testosterone levels than others.
The biologists examined behavior and hormone profiles in nearly 30 individuals of Eulemur.
In four of the species (Eulemur rubriventer, E. macaco flavifrons, E. coronatus, E. mongoz), females are at the top of the pecking order, and in the other two species (E. fulvus collaris, and E. f. rufus) the sexes have equal status.
The dominant females had significantly higher male hormone levels than the females from the two more egalitarian species.
“It’s strong evidence that hormones are playing a role. Lemurs and lorises split off from the rest of the primate family tree more than 60 million years ago, but the two species of egalitarian lemurs didn’t evolve until much more recently, within the last 2 million years,” said Petty, who is the lead author of a paper published in the journal Scientific Reports.
“It could be that females are more sensitive to the effects of testosterone than males, stimulating aggressive behavior even though males still have more of the hormone.”
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Joseph M. A. Petty & Christine M. Drea. 2015. Female rule in lemurs is ancestral and hormonally mediated. Scientific Reports 5, article number: 9631; doi: 10.1038/srep09631
