Manes vary from light blond to black and can be up to a foot long. Maneless adult males occasionally are observed in the Serengeti Plain of Tanzania, and lions in Kenya's Tsavo National Park are mostly maneless. But males of two subspecies now extinct in the wild, the Barbary lion of the Atlas Mountains and the Cape lion of mountainous regions of South Africa, sported giant dark manes that covered their stomachs.
"On a broad scale, it's been known for at least a century that lions in colder climates have long dark manes," said Peyton West, a graduate student in the College of Biological Sciences' department of ecology, evolution and behavior and first author of the study. "But no one knew why lions had manes or why there was variation within specific populations. We wanted to find the costs and benefits to individuals of having a big or dark mane."
Manes may offer protection in a fight, but West and her adviser, Distinguished McKnight University Professor Craig Packer, suspected that a more important function is to intimidate other males. This would be an obvious advantage to male lions in defending their prides against potential rivals. Also, a male that advertises his ability to defend a pride and its cubs should appear attractive to females.
To find out how the two sexes responded to different types of manes, West, working in Serengeti National Park, set up pairs of realistic-looking dummy lions about 200 meters from adult lions. To test reactions to different mane length, she paired dummies with short blond or long blond manes. In separate experiments to observe reactions to mane color, she paired dummies with long blond or long dark manes. When the dummies were in place, she broadcasted recordings of a hyena at a kill--the leonine equivalent of a dinner bell--and noted reactions of the lions when they spotted the "intruders."
Male lions were clearly intimidated by long manes and dark manes, said West. Given a choice between short and long manes, males approached the short-maned dummy nine out of 10 times. In the one instance where the long-maned dummy was approached, the males were relatively old, with long, dark manes. Even then, they approached from the side; males never approached a long-maned dummy directly. When confronted with light and dark manes, males always (five of five times) chose to approach the light-maned dummy.
Females showed a preference for the darker-maned dummy, approaching it rather than the blond one nine of 10 times. When West and Packer later examined long-term data (recorded by Packer and his colleagues) on females who had had a choice of males in their prides, the females chose the darkest-maned male in 13 of 14 cases. But neither the long-term data nor West's dummy experiments showed any clear female preference for long or short manes.
When West and Packer examined the data on several dozen males that had been sedated and had blood samples drawn, they found a strong correlation between blood testosterone levels and mane color.
"Dark color tends to be found in high-testosterone males," said West. "Therefore, it isn't surprising that females would prefer darker manes and males would be intimidated. But there is no correlation between testosterone and mane length. We figure males are sensitive to an opponent's mane length because recently injured lions have shorter manes." Females may not care as much that a male is recovering from injury because accidents can happen to even the fittest males, she said.
Males with dark manes pay a price for their imposing--and sexy--appearance. Using an infrared camera to record the body temperatures of Serengeti lions, West found that males were hotter than females. At first glance, this could have been a consequence of males' larger size and smaller surface-to-volume ratio, which could hamper heat loss. But when she took the temperatures of maneless Tsavo lions, she found no difference between males and females.
"A male with a dark mane may have to work harder to stay cool, behaviorally or physiologically, and is advertising that toughness, along with his toughness in battle," said West. "But we didn't find that longer-maned males were hotter than those with shorter manes. It appears that beyond a certain length, there's no further cost to having a mane."
The lion's mane functions much like the peacock's tail; it's a visual cue indicating a male's health and fitness, said Packer. But it's also a cue that humans should pick up.
"As climate changes, things like lion manes, the brightness of bird plumage and the size of deer antlers may be sensitive bioindicators," Packer said. "They can tell you how well an animal is doing in the environment."