The lion's mane has long been an iconic symbol, yet there has been no clear answer as to why lion's have manes, or what function they serve. We have spent the last seven years
addressing this question using a wide variety of information collected through observations, experiments, and physiological assays such as hormone analyses.
Lions are the only cat with a mane, as well as the only social cat, so it stands to reason that the mane may be related to social behavior. Charles Darwin was the first to suggest that the mane may be a result of "sexual selection" meaning that the mane may play a role in reproductive success. One hypothesis has been that the mane protects a male's neck in fights with other males, and that males that are more successful in fights would then have increased access to females. Another hypothesis is that the mane serves as a signal of male condition allowing males to assess each other's fighting ability and females to choose superior mates.
Our studies addressed both hypotheses. If the mane evolved by conferring protection on male necks, one might predict that the area covered by the mane is a special target of attacks during fights. Additionally, wounds to the neck area might be particularly dangerous. In these cases, there would be significant evolutionary pressure on males to develop protection in the neck area. However, when we examined wounding patterns both in adult males, and in females and sub-adult males (whose neck areas are bare), we could find no evidence that the necks were special targets, nor that wounds to the neck were especially dangerous. These results suggested that the mane's primary function might be to signal male condition.
We tested this idea by using life-sized "model" lions with differing manes. These models were generously donated by Anna Club Plush toys of Holland and were made to exact specifications based on measurements and hair samples from real lions. These models allowed us to observe how real lions responded to variation in male manes. After finding a group of lions, we set up two of the models and fitted them with manes that differed in either mane length or in mane color. We then attracted the lions' attention by broadcasting the sounds of hyenas at a kill (a dinner bell for lions), and watched to see which of the models the real lions chose to approach. The results were startlingly clear: male lions approached shorter and lighter manes, apparently finding them less intimidating. In contrast, females were indifferent to mane length, but they approached dark manes 9/10 times, seeming to find darker manes more attractive.
These findings suggested that the mane is indeed a signal to other lions, but they left several questions unanswered; first, what information does the mane convey? Second, if longer, darker manes are advantageous to males, why don't all male lions have long, dark manes?
To answer the first question, we turned to our long-term records which allowed us to compare the mane color and length of individual males (determined by analyzing photographs) to measures of male fitness including injury, testosterone levels (determined through analysis of blood samples), and offspring survival. Our data confirmed what the model tests had suggested. Males with shorter manes had often been injured or sick suggesting that mane length conveys information about current fighting ability. Males with darker manes were older, had higher testosterone levels, were more likely to recover from injury, spent more time resident with prides, and had higher offspring survival. Thus, mane color appears to convey information about male maturity and experience, testosterone-related aggression, and potential reproductive success.
These answers tell us that the mane conveys important information, but they fail to explain the variability seen in mane length and color. Generally, in studies of sexual selection, such variation is a result of the costs imposed by the sexually selected trait. For example, the male peacock's tail makes him more vulnerable to predation, and males with more exaggerated tails are also more vulnerable. We anticipated a similar situation with lion manes. Using an infrared camera, we measured the surface temperatures of male and female lions, and found that male lions were hotter than females. In addition, males with darker manes were hotter than males with lighter manes. These results suggest that the mane imposes costs in terms of heat stress, and that only superior males can afford to withstand these costs. For inferior males, a dark mane would be a serious handicap such that the costs would outweigh the reproductive benefits.
Ultimately, our research provides good evidence that the mane is a sexually selected signal by which a male advertises his condition to other lions. It also highlights the importance of temperature to lion ecology and behavior and to sexual selection in general. These findings are the subject of a paper in the August 23rd issue of SCIENCE magazine entitled "Sexual Selection, Temperature and the Lion's Mane" by Peyton West and Craig Packer. This paper can be read on line by following the links below.
Infrared Thermography and the Mane
Infared thermography is a technique which measures infrared radiation and converts these measurements into measures of surface temperature. This technique was instrumental in helping us identify the heat related costs of the lion's mane.
An infrared camera takes digital pictures, and each pixel in the picture corresponds to a specific temperature. The technique is astonishingly accurate (usually to within 0.1° C) and the cameras are hardy and portable making them ideal for a field study. Unfortunately, the cameras are also extremely expensive, but in 1999 we received a special supplement to our National Science Foundation research grant to support a 3 month rental of an infrared camera. Thanks to special assistance from Flir Systems Inc. (a manufacturer and distributor of infrared technology), we obtained a camera in June, 2000 and again in May, 2001 and brought them to East Africa.
Our hypotheses were that males are generally hotter than females, and that males with darker or longer manes are the hottest of all. We addressed these hypotheses by taking infrared images of males and females in the Serengeti and Ngorongoro. We found that Serengeti/Ngorongoro males were hotter than females but it was impossible to determine whether this difference arose because males are bigger (lowering their surface area: volume ratio) or because of the male's mane. To answer this question we traveled to Tsavo East in Kenya, where the males are largely maneless. In Tsavo, as in the Serengeti, males are bigger than females, but when we measured their surface temperatures we found that they were no hotter than females. This allowed us to infer that in the Serengeti, it is the male's mane which makes him hotter than females.
When we compared the surface temperatures of individual males in Serengeti/Ngorongoro, we found that males with darker manes were hotter than those with lighter manes. This suggested that darker-maned males pay a higher cost in terms of heat stress. Analysis of our long-term data supported this supposition; high temperatures interfere with sperm production, and males with darker manes had more abnormal sperm. Eating large meals is known to increase heat load and males with darker manes at less in hot months; thus it appears that when temperatures rise, males with darker manes must limit their food intake to stay cool.
Research conducted in association with the Tanzania Wildlife Research Institute
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Last updated on November 9, 2004