Baboon males fight ferociously for power, only to have that power bite back.
Top-ranking males generate surprisingly high levels of stress hormones, a sign that these primates pay a cost to be the boss, report evolutionary biologist Laurence Gesquiere of Princeton University and her colleagues in the July 15 Science.
Stress-hormone levels in alpha males are on par with those of low-ranking males scuffling to survive, the study showed. Baboon bosses are burdened by having to fight off rivals and guard fertile mates from others’ advances, the scientists propose. Meanwhile, indignities such as not getting enough to eat and enduring harassment by higher-ranking males stress out bottom dwellers.
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“Alpha males have higher reproductive success than other male baboons, but those benefits come at a significant cost,” Gesquiere says.
The top males’ second-ranking peers are not nearly as hard-hit by stress hormones, the scientists found, although alpha and beta males exhibited equally high concentrations of the male sex hormone testosterone, a marker of aggression and social dominance.
Power’s stressful fallout contributes to a consistent turnover of alpha males, Gesquiere proposes. Earlier studies suggested that a combination of elevated stress hormones and sex hormones lowers a baboon’s immunity to disease over time.
The new findings indicate that “life is considerably more stressful” for alpha males than for baboons one rung lower in status, writes Stanford University biologist Robert Sapolsky in a commentary published in the same issue of Science.
Sapolsky and other baboon researchers have found that low-status males collectively have higher stress-hormone levels than high-ranking males. Stress-hormone spikes appear in groups of high-ranking males only during occasional periods of social turmoil, when their hold on status is in jeopardy.
Gesquiere and her colleagues find that these previously reported differences between groups mask the tendency of alpha males in particular to have stress-hormone levels as high as those of their lowest-ranking comrades. Her team tracked social rankings of 125 adult male baboons living in five communities in Kenya’s Amboseli National Park from 2000 through 2008. Monthly status rankings were calculated from the number of wins and losses for each animal in fights and confrontations. The scientists also measured hormone concentrations in each baboon’s feces monthly.
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In a previous study of Amboseli baboons, researchers found that alpha males mate with fewer females, and beta males mate with more females, than expected given their social standings. Alpha males’ stress may stem partly from this mating underachievement, though the loss isn’t great enough to keep males from striving to be number one, remarks biological anthropologist and baboon researcher Jacinta Beehner of the University of Michigan in Ann Arbor.
Something akin to the intensified stress profile of alpha-male baboons may characterize hard-charging human CEOs fighting to fend off business rivals and takeover bids, Beehner suggests. “It would not be surprising to find that being at the top is not all it’s cracked up to be.”