Why Lions have Manes?
© Wingate, L. 2005 Imvubu 17: 3, 7
The lion’s mane has long been an iconic symbol, yet there has been no clear answer as to why male lions have manes or what function they serve. Peyton M. West and Craig Packer have spent the last seven years addressing the question using a wide variety of information collected through observations, experiments and physiological assays, such as hormone analyses. Their findings are as follows:
“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 behaviour. 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 in adult males, 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 colour. 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. Firstly, what information does the mane convey? Secondly, 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 colour and length of individual males (determined by analysing 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 colour 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 colour. 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 behaviour and to sexual selection in general.”
Source: West, Peyton and Craig Packer (2005) “Sexual Selection, Temperature and the Lion’s Mane.” SCIENCE, 23 August [Department of Ecology, Evolution and Behaviour, University of Minnesota, 1987 Upper Buford Circle, St. Paul, MN 55108, USA].