A reprint from American Scientist the magazine of Sigma Xi, The Scientific Research Society This reprint is provided for personal and noncommercial use. For any other use, please send a request to Permissions, American Scientist, P.O. Box 13975, Research Triangle Park, NC, 27709, U.S.A., or by electronic mail to [email protected]. ©Sigma Xi, The Scientific Research Society and other rightsholders The Lion’s Mane Neither a token of royalty nor a shield for fighting, the mane is a signal of quality to mates and rivals, but one that comes with consequences Peyton M. West he African lion is one of the world’s the lion’s mane—I was hooked. The Tmost admired and best studied possibility of answering such a basic species, yet its most striking feature question was exactly the reason I got has long been a mystery: Why do li- into science in the first place. I soon ons have manes? Charles Darwin, who joined Craig’s lab despite his warning: knew almost nothing about lions, was “it’s not an easy project….” one of the first to suggest an answer, Three basic features guide any writing, “The mane of the lion forms thinking about the lion’s mane. First, a good defence against the one danger the mane is sexually dimorphic (only to which he is liable, namely the at- males have manes); second, the mane tacks of rival lions.” This unsupported begins development at puberty; and hypothesis prevailed until 1972, when third, the mane is highly variable both George Schaller published his semi- within and between populations. nal work, The Serengeti Lion. Schaller Manes vary in color from almost white suggested that males bore sumptuous to deep black and in overall size from manes to signal their quality as a pro- the slightest “Mohawk” and side- spective mate, similar to the displays whiskers to a long, thick coat that cov- of several other polygamous species. ers the shoulders and chest. Further- Although these two hypotheses were more, individual manes are not uni- not mutually exclusive, scientists tend- formly sized or colored but are often a ed to favor one or the other. When I be- patchwork of lengths and hues. These gan my research in 1995 neither theory features are consistent with the idea had been systematically tested. that the mane is a product of sexual Craig Packer introduced the ques- selection. Most sex-selective traits are tion to me in a casual conversation sexually dimorphic, begin development about potential thesis projects, months at puberty and are highly variable. Ac- before I started graduate school at the cording to the theory of sexual selec- University of Minnesota. “There are tion, such characteristics evolve under really two big mysteries left about the stress of competition for mates. the big cats,” he said. “Why did sa- Sexually selected traits can increase ber tooth tigers have saber teeth and reproductive success in two ways. The why do lions have manes?” I remem- first, known as male-male competition, ber thinking that there wasn’t much I increases the ability of males to com- could do about saber tooth tigers, but pete against other males for females. Figure 1. Manes are unique to lions—no other Traits in this category include armor to cat species has them, so they must serve some specialized function. Yet the purpose of the Peyton M. West earned an undergraduate degree protect males from opponents, weap- in English literature from Yale University, where ons to disable opponents or signals of she avoided science classes altogether. A love of fighting prowess that males use to as- more offspring, or indirectly, through animals led her to take several years of biology sess opponents. Generally, males with better genes for their offspring. One of coursework, coincident with an internship at the more exaggerated features are better our objectives was to determine wheth- Beardsley Zoo in Bridgeport, Connecticut, and a competitors. The second role of sexu- er the mane functioned in male-male full-time job studying recombination in the soil ally selected traits, mate choice, increases competition, mate choice or both. bacterium Acinetobacter calcoaceticus. She re- male attractiveness to females. Traits of ceived a Ph.D. in ecology, evolution and behavior from the University of Minnesota in 2003 and this sort, such as bright coloration, long Serengeti Story worked in the Mammal Department at the Bronx feathers or elaborate calls, usually relate When Craig said studying the mane Zoo before taking time off to have a baby. Address: to the male’s condition. Females that would be challenging, he knew what 1524 29th Street NW, Washington, DC 20007 prefer more “ornamented” males may he was talking about. He has studied Internet: [email protected] obtain benefits directly, in the form of lions in the Serengeti National Park in 226 American Scientist, Volume 93 © 2005 Sigma Xi, The Scientific Research Society. Reproduction with permission only. Contact [email protected]. male lion’s mane remained unverified until recently. The author's work in East Africa provides comprehensive evidence of the mane’s function as a proxy for overall fitness. Depending on the context, lions of both sexes consider mane characteristics when sizing up a male lion. This picture shows a male guarding his chosen female (in repose) on the Serengeti plains. (All photographs courtesy of the author unless otherwise noted.) Tanzania for almost 30 years and en- that are difficult to answer for wild females typically join their mother’s dured all sorts of grueling ordeals in populations. Studying sexual selection pride, and young males form “coali- the name of scientific exploration. His in the field, in a long-lived species like tions” and disperse to look for their hard work made my job easier though, the lion, would have been impossible own pride. This creates a system in because thanks to his efforts and those without this prior research. which a small group of males can of other scientists, there is a vast data- To start with, knowledge of lions’ monopolize many females, leading base on the Serengeti lions. Not only social structure allowed us to refine to severe reproductive competition. has this work answered most questions our hypotheses about sexual selection. Predictably, males compete intensely about lion behavior, but demographic Female lions live in prides consisting for mates, and they compete on two and physiological data let us study the of related females and their dependent levels. At the group level, male coali- heritability of traits and other questions offspring. As the cubs grow, young tions vary in size, and larger coalitions www.americanscientist.org © 2005 Sigma Xi, The Scientific Research Society. Reproduction 2005 May–June 227 with permission only. Contact [email protected]. Corbis Figure 2. Manes can be short or long, nearly black or almost white. The length and color vary considerably within a group, but the greatest variety lies between populations that inhabit different climates. An individual lion’s mane may demonstrate a patchwork of hues (left) or show a more con- sistent coloration (center). Mane length is also variable: A few hundred miles east of Tanzania’s Serengeti National Park, the adult males in Kenya’s Tsavo National Park have extremely short manes, frequently bearing only vestigial side-whiskers and a tufty sprout atop their heads (right). sire more offspring than small coali- benefit from a shield to protect them short term, a group of females can tions. Individuals within a coalition during fights. However, avoiding the fend off infanticidal newcomers, but also compete: If a male discovers an fight altogether would be a greater the pride’s resident males bear most of estrous female, he will jealously guard advantage; thus, males would benefit the responsibility for protecting young her and prevent her from mating with from a signal that conveys their fight- lions. The displacement or loss of a his companions. As Craig and his ing ability to rivals. male coalition generally leads to 100 colleagues discovered, this behavior From the females’ perspective things percent mortality of any unweaned skews the paternity rates for individu- are slightly more complicated. Unlike cubs. Females would thus benefit from als in larger male coalitions. many mammals, male lions play an a signal that advertised a male’s ability In contrast, female lions are egali- important role in raising offspring, to fight off would-be usurpers. tarian. Unlike some social carnivores, but they are also utterly intent on their Males also help feed the pride. Al- such as wolves and hyenas, all of the own reproductive fitness. When a new though male lions are often depicted as adult females in a pride reproduce, coalition of males joins a pride, they parasites, lying around while females and female lions don’t have a domi- immediately kill or evict the offspring do all the work, males are extremely ca- nance hierarchy, which often dictates of the previous males. This behavior pable hunters of a key prey species: the reproductive success in other species. accounts for more than 25 percent of Cape buffalo. Buffalo are large and slow, Furthermore, a key attribute of lion cub deaths and is a major variable in and hunting them depends less on the society is that females breed synchro- female reproductive success. In the speed and agility evinced by females nously, which means that there are often more estrous females available at one time than there are resident males. Males cannot usually defend more than one female at a time, but they willingly mate with additional females if possible. Thus, if estrous fe- males outnumber males, the “excess” females—those that aren’t actively guarded—are free to choose among coalition males.