The Lion's Mane

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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 consistent 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 females outnumber males, the “excess” females—those that aren’t actively guarded—are free to choose among coalition males. The bottom line is that this social system provides op- portunities for sexual selection based on male-male competition and mate choice. This combination is not en- tirely surprising. Although historical studies of sexual selection focused on one or the other hypothesis, more recent work demonstrates that the two mechanisms often operate together. More than 30 years of field observations also helped answer our next Figure 3. Charles Darwin proposed that male lions had manes to shield their vulnerable head question: What kind of trait would and neck from the teeth and claws of other lions. If the mane did evolve to shield its owner, be most useful to lions? With lethal then attacks to these areas would probably be more frequent during fights. However, the au- claws and teeth, fighting is very costly, thor’s analysis of records from witnessed fights and an extensive database of injuries showed even for the victor. For this reason, that wounds to the mane area were no more frequent or lethal than wounds to other parts of just as Darwin suggested, males might the body—even for females and subadults, which lack manes.

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Figure 4. Like other sexually selected traits, the lion mane is sexually dimorphic, begins to develop at puberty and is highly variable. The mane of a male lion usually starts to darken before his first birthday and continues to do so for the next four to five years (left). Over the same time period, mane length and serum testosterone show similar increases. However, the manes of individual lions can become darker or lighter during adult- hood because of injury or dietary changes, as demonstrated by the records of four individuals over a period of several years (right). and more on the weight and strength the mane is an effective barrier against cifically: What ecological trends predict characteristic of males. A buffalo will the teeth of rival lions, and that males mane length and darkness? A critical satiate a big pride, and this species is with longer or darker manes are in- first step was to quantify objectively the most important prey throughout jured less frequently or less severely. the length and darkness of a lion’s much of the lion’s range. For females, Unfortunately, these predictions are mane. For this task we turned to our such contributions are critical because almost impossible to verify. Fights be- photographic archives, which included starvation is another common cause of tween lions are rarely witnessed, and pictures of virtually every male lion to death among cubs. Any trait that adver- individuals are seldom seen regularly appear in our study area since the proj- tises male hunting ability or contains enough to assess the frequency with ect began in 1966. While in the field, general information about a male’s nu- which they are wounded. Instead, we continued to photograph males ev- tritional status would be valuable. we generated two related hypotheses ery six months to document new ani- This knowledge allowed us to re- that were testable. First, we predicted mals and record any changes in their fine our thinking before beginning our that if the mane’s primary function manes. We then recruited undergradu- fieldwork. We hypothesized that the was protection, the “mane area,” or ate students, who were informed of the mane might function in any of three the area of the body covered by mane general nature of our work but knew ways: as a shield against injury, as a hair, would be a special target dur- nothing about the individual animals, signal of the male’s ability to fight and ing fights and that most lion-inflicted to “grade” the pictures for length and protect his cubs (essentially the same wounds would be found there. Sec- darkness. At least five students graded thing), or as a sign of the male’s nu- ond, we predicted that wounds to the each picture; we then eliminated the tritional status. The physiological at- mane area would be more serious and low and high scores and averaged the tributes of hair support the idea that it more likely to be fatal. remainder. These measurements be- could convey such information. Hair We addressed our hypotheses by came the backbone of our research. growth depends on a variety of fac- combing the records for descriptions of We first used these data to address tors, including, among other things, injuries and eliminating those wounds several long-standing questions about hormones, health and nutrition. In sex- that were not inflicted by other lions. lion manes. We ascertained, for exam- ual selection terms, hair is “condition- From these observations we created ple, that manes in the Serengeti gener- dependent,” meaning that its appear- a database that included the loca- ally begin developing at just under one ance is often related to the underlying tions and survival rates for wounds year and continue growing until males condition of the animal. More specifi- to males, females and subadult lions. reach 4.5 years of age. The mane gains cally, hair growth and pigmentation are These data did not support the mane- pigment rapidly during this time, until influenced by testosterone, which in as-shield hypothesis. Wounds to the the color becomes more stable about a turn is related to aggression and might mane area were no more frequent year after growth ends. It continues to be an indicator of fighting ability. Addi- or lethal than those to other parts of darken at a slower rate throughout life. tionally, malnourished and sick mam- the body. The observations were true We also demonstrated that the age- mals often develop rough, unhealthy- not only for adult males but also for related increases in length and color looking hair, and poor nutrition, such females and subadults, which lack mirrored the increase in testosterone as copper and zinc deficiencies, can in- manes. It seems that a lion’s teeth pro- during adolescence. hibit hair growth and pigmentation. vide more than enough incentive to A welcome surprise was that the avoid tangling with the front end. manes of individual males were not The Meaning of the Mane Finding little evidence to support always constant over time; although Our first goal was to address the the mane-as-protection hypothesis, we the pattern of sharp gains in length mane-as-a-shield hypothesis, which turned to the idea that the mane func- and color followed by slow darkening makes two simple predictions: that tions primarily as a signal, asking spe- was typical, the manes of some lions

www.americanscientist.org © 2005 Sigma Xi, The Scientific Research Society. Reproduction 2005 May–June 229 with permission only. Contact [email protected]. became lighter or shorter, or changed advantage of it, but demonstrating the suggesting that mane darkness does back and forth. These results were truth of this principle can prove chal- predict male dominance. inspiring because they gave further lenging. Our next step was to look for We next turned to females, and here credence to the idea that the mane is evidence in our long-term records that our long-term data proved more useful. condition-dependent—this kind of males and females were actually us- Because “excess” estrous females choose variation in sexually selected traits of- ing the information contained in the their own mate, we looked among the ten reflects changes in the underlying manes. For males, this proof was par- records for situations in which a male condition of the animal. ticularly difficult to get. We knew from mated with more than one female in More generally, our analysis re- previous research that dominance rela- the course of an hour, assuming that vealed that mane length and darkness tions in male coalitions do occur—in at least one of the females was there by are correlated with several ecological coalitions consisting of three or more choice and was therefore exercising a factors. In males older than five years, males, generally only two males fa- preference. We found 14 examples of mane length was most closely associ- thered all of the offspring—but we this situation for which we also had ated with injury. Prior to starting the were unable, because of incomplete good data on the mane characteristics of analysis, we knew anecdotally that photographic data, to link these rela- all the males in the coalition. Again the the manes of injured males were often tions to mane characteristics. results contained a surprise. Like coali- reduced and could fall out altogether, Instead, we turned to an experimen- tion males, females appeared to place and we now discovered that injured tal protocol used by previous lion biol- little value on the length of the mane— males also had more subtle reductions ogists: playbacks. This technique uses in only seven of these examples did the in mane length. This fact is significant recordings of natural animal sounds to male in question have the longest mane because it suggests that mane length mimic situations that we would other- of his coalition. However, color was might signal a male’s current fight- wise seldom witness. We broadcast again a critical factor. In 13 of the 14 ob- ing ability—injured males should be the roars of single, unfamiliar females servations, the females mated with the less able or less aggressive fighters. to coalition males in order to evoke male whose mane was darkest. Mane color proved more interesting male competition for access to an es- The consistent results indicated that still: In addition to the age effect, we trous female. Because the first male to mane darkness played a role in sexual found that males with darker manes reach an estrous female generally ends selection, but they left some nagging had higher levels of testosterone, sug- up guarding and mating with her, we questions. Why didn’t lions pay atten- gesting greater aggression, and were reasoned that whichever male led the tion to mane length when it could be- on average better fed throughout group would most likely be dominant. tray recent injury? And how did lions the year, suggesting either general If mane color or length were indica- respond to strangers, whose arrival had dominance or superior hunting abil- tions of dominance, we predicted that such potentially disastrous consequenc- ity. These results implied that both the male with the darker or longer es? Observational data were inadequate length and color provided interesting mane would be the first to the loud- because such meetings are rare, occur information for other lions, and that speaker. Experiments with 13 resident mostly at night and are impossible to both males and females would benefit male coalitions uncovered a reveal- predict. Thus, we again turned to active from using it. ing and surprising result. Mane length experiments, presenting to the real lions had little relation to “dominance,” as “dummies”—two plush, life-sized toy Shorthand for Quality measured by our tests, but males with lions that differed only in their mane— Signaling theory predicts that if infor- darker manes were significantly more to see if mane characteristics influenced mation is available animals will take likely to win the race to the female, the lions’ behavior.

Figure 5. The lion’s mane often shortens considerably and can even fall out altogether when an animal is wounded. These two photographs show the same lion, “Trojan,” within a six-month period before (left) and after receiving an injury in a fight with another lion. He was last seen a few months after the second photograph was taken.

230 American Scientist, Volume 93 © 2005 Sigma Xi, The Scientific Research Society. Reproduction with permission only. Contact [email protected]. Fool Me Once… We were optimistic about this approach. Ecologists commonly use dummies to study sexual selection in other species, and another graduate student from the Packer lab had successfully used a lion mount (prepared by a taxidermist) in earlier experiments. However, getting the actual dummies was a problem. We couldn’t find a source for large, realistic stuffed lions, and custom-made toys were prohibitively expensive. Then, in a stroke of serendipity, Craig was con- tacted by a documentary filmmaker, Brian Leith, who wanted to make a film about lions. Brian was captivated by the experiments we were planning, and in no time at all he discovered Anna Club Figure 6. To see if a lion’s mane relates to his relative dominance within a coalition of males, Plush, a Dutch company that was will- the author broadcast the roars of an unfamiliar female lion from a hidden speaker, an act that ing to donate stuffed toy lions made to prompted all the local males to investigate. The scientists reasoned that because the first male to encounter an estrous female usually becomes her mate, the dominant male in a coalition would our specifications. Within a few months, most often lead the group. Although mane length did not predict the order in which male lions four beautifully plush, life-sized male arrived, ones with darker manes were significantly more likely to reach the “female” first. lions arrived in the Serengeti. We chris- tened them Romeo (short, dark mane), a group of lions, we waited until dusk lions? Happily, it was clear from the Lothario (short, blonde mane), Julio (when lions are more active), set up the outset that we were getting good data. (long, dark mane) and Fabio (long, decoys downwind (to mitigate any ef- After a quick start toward the loud- blonde mane). fect of scent) and broadcast recordings speaker, the real lions became much In each experiment we presented a of hyenas at a kill. This cue evoked a more cautious when they caught sight choice between two dummies to single- speedy response from the lions, who of the plush ones, stopping for a care- sex groups of adult lions. Lothario and gathered to scavenge a meal. As they ful look every few feet before proceed- Fabio helped us test the importance of approached, the lions quickly noticed ing. On reaching a dummy, often their mane length, and we used Julio and Fa- the two “strangers,” and their attention first act was to sniff under its tail. To bio to test the effect of mane darkness. shifted to the dummies. At that point, eliminate the effect of scent on their The manes were attached with Velcro, a we turned off the sound and watched. behavior, we noted on which side the feature that allowed us to switch manes The early experiments were nail- lions approached the dummies, be- and control for any differences between biting affairs. Would the protocol cause they usually made that decision individual dummies. Once we found work? Could the dummies fool real at a distance of 100 meters or more. Thus, a female approach on the side of the dark-maned dummy counted as a preference for the darker mane. Although the initial experiments were promising, it took three years to get enough data to draw meaningful conclusions: To our great surprise, the lions soon became habituated to the dummies. Lions that had seen them before—even years before—were nev- er really fooled again. Their behavior was much less cautious, and they often failed to approach at all. Because lions live in fission-fusion groups, the project became much, much more complicated. Even if three out of four lionesses were dummy “virgins,” we couldn’t test the group—all four had to be naive. Furthermore, because the tests of males required resident coalitions (nomadic males would flee rather Figure 7. The fundamental unit of lion society is a pride of related females that is dominated and protected by a smaller number of allied males. Females in a pride come into estrus syn- than approach the strange males), we chronously, but during this time each male is able to guard only a single female from advances had to expand beyond our study area by other males. Thus, so-called “excess” females can choose which male to approach as a pro- to get an adequate sample size. But our spective mate. In 13 of 14 cases, females chose to copulate with the male that had the darkest reward for all this work was a fascinat- mane among coalition members. Mane length was not a significant factor in female choice. ing set of data. www.americanscientist.org © 2005 Sigma Xi, The Scientific Research Society. Reproduction 2005 May–June 231 with permission only. Contact [email protected]. Figure 8. The use of dummy lions—life-sized plush toys with mix-and-match manes— allowed the author and her colleagues to test the effects of mane length and darkness on the interactions between unfamiliar lions. The four toy lions sported colorful names as well: (left to right) Romeo (short, dark mane), Fabio (long, blonde mane), Julio (long, dark mane) and Lothario (short, blonde mane).

simulated interactions between unfamiliar males. Because mane length can indicate short-term quality in the form of recent fighting success, this signal may be more relevant when deciding to challenge an unfamiliar opponent than when dealing with a well-known, long-term confederate. We had established that the mane Similar to the long-term mating re- ever, unlike the playback study, the acts as a signal to other lions, but cords, females in this test strongly pre- tests with Lothario and Fabio showed what were the actual benefits of hav- ferred dark manes, approaching on the that males were extremely sensitive to ing or preferring dark or long manes? side of the black-maned dummy nine mane length; they avoided the long- A further look at our long-term re- out of ten times. They approached the haired dummy in favor of the short- cords filled in these gaps. Although longer-maned dummy in only seven haired one in nine out of ten tests. The mane length had no detectable link of ten trials (a nonsignificant result). different results arose from the differ- with overall fitness, mane darkness Similarly, males were sensitive to mane ent contexts for the two experiments: was a significant factor. Males with darkness, avoiding the darker-maned Whereas the earlier study tested domi- darker manes spent more of their lives dummy in five out of five trials. How- nance within a coalition, the plush lions residing with a pride and were more

Figure 9. The life-sized dummies provided a tool for testing each sex’s response to a pair of unfamiliar lions whose manes varied by length or color. Consistent with the observation that “excess” females in a pride chose mates with dark manes, females who encountered Fabio and Julio approached the latter 90 percent of the time (a). By contrast, male lions avoided the darker “stranger” in four of five trials (b). Females showed less preference for mane length, opting to examine Fabio rather than Lothario in 70 percent of the experiments—a nonsignificant result (c). However, males were wary of the long-haired decoy, cautiously approaching on the side of the short-maned dummy in 90 percent of trials (d). Unlike the earlier study of male lions that found no relation between mane length and dominance within a coalition, this experiment’s simulation of an encounter between unfamiliar males indicates that they do attend to mane length when estimating the fighting prowess of an unknown rival.

232 American Scientist, Volume 93 © 2005 Sigma Xi, The Scientific Research Society. Reproduction with permission only. Contact [email protected]. likely to survive when wounded. Fur- thermore, their offspring were more likely to reach their second birthday (which also benefits females that chose dark-maned males) and less likely to be wounded, suggesting that darker- maned males provide better protection from other lions (the most common cause of injury).

Degree of Cost The analysis showed several benefits of having a dark mane. So why don’t all males have them? In other words, what prevents “dishonesty” among males who are wooing prospective mates? This is a common question in the study of sexual selection. Scientists generally answer that the production or maintenance of such a phenotype �� must be so costly that only superior males can afford it. So what is the cost of a black mane? Heat. �� Since the early 20th century, natu- �� ralists such as Frederick Selous have noted that lions in different regions �� had different mane characteristics,

and they even linked this variety to �� temperature. Males in colder, higher- �� altitude habitats tend to have bigger, darker manes than those in hot, humid climates, and all lions are extremely �� sensitive to heat. Larger animals have �� more difficulty with high tempera- �� tures because of their higher ratio of �� volume to surface area, and many lion �� behaviors seek to minimize heat stress. Sleeping in the day and limiting most �� activity to the night is one example; �� others include lying on their backs �� to expose their thin-skinned bellies, �� resting on high rocky knobs to catch �� the breeze, and panting after exertion �� or large meals. Unlike dogs, lions do �� not have cool, wet noses, and unlike �� people, they don’t sweat. Their only means of thermoregulation are breath- �� ing (panting) and radiating heat from �� the skin. In this context, the mane is a �� handicap because it prevents the effi- �� cient dissipation of heat. Furthermore, Figure 10. A male lion runs the risk of heat stress in exchange for having a long, dark mane. Un- dark hairs are thicker than light hairs, able to sweat, lions must dissipate heat through panting and radiation—mechanisms that are creating a better insulator, and dark inadequate when the mercury climbs. Remote thermography of a trio of lions (top) shows that surfaces absorb more solar energy the surface temperature of the standing male is higher (more yellow) than those of the two re- than light ones. clining females (more orange). This temperature difference between sexes does not exist among These facts suggest that heat stress lions in Tsavo National Park (a hotter and more humid area where males have slight manes), might be the most significant cost as- suggesting that the mane is linked to the buildup of heat. A higher body temperature has negative consequences, including an increased incidence of deformed sperm; not surprisingly, dark- sociated with the mane, and that lions maned males show fewer normal sperm than light-maned males from the same region. Even with long, dark manes would be most the metabolic heat generated by the digestion of a big meal can become taxing at the edge of the affected. Testing these hypotheses was lion’s climatic range. Male lions in the Ngorongoro Crater eat less (judging by measurements of challenging—we couldn’t exactly use a belly size from photographs) when the weather is hot than during cool periods (upper graph). thermometer on wild lions. However, However, this restriction appears to apply preferentially to males with dark manes (lower the technology of infrared thermog- graph). The scoring system for lion bellies uses a scale of 1 (the fattest) to 5 (the skinniest).

www.americanscientist.org © 2005 Sigma Xi, The Scientific Research Society. Reproduction 2005 May–June 233 with permission only. Contact [email protected]. Figure 11. The African lion’s sensitivity to temperature leads to behaviors that increase heat dissipation, such as the practice of resting high on rocky outcrops, or kopjes, to catch the breeze. Global warming will probably mean that long, dark manes, which trap heat, will become rarer in the future. raphy, which can measure the precise In support of our heat-stress hypoth- ling for ambient temperature, wind, surface temperature of a distant object, esis, Tsavo was noticeably hotter and humidity and prior activity. This con- held some promise. The latest genera- more humid than the Serengeti, and the nection supported our prediction that tion of such cameras was sufficiently lions there appeared to be more chal- males with darker manes paid a high- portable to bring to the field, and a lenged by the climate. For example, we er price in terms of heat stress. In ad- manufacturer, Flir Systems Incorpo- observed the novel behavior of scrap- dition, we confirmed that males with rated, agreed to let us rent one of the ing away the topsoil before lying down, darker manes had higher proportions pricey devices at a discount. presumably to find cooler earth under- of abnormal sperm (the link between We spent three months snapping in- neath. Yet aside from their manes and testicle temperature and sperm pro- frared pictures of all the adult males in their heat-related adaptations, Tsavo’s duction is well known). We also found the area, as well as many females and lions were virtually identical to Serenge- that unlike light-maned males, dark- subadults. Our first step was to compare ti lions in appearance and behavior, and maned males reduced their food in- the average surface temperatures of the the sizes of prides and coalitions were take in hotter weather. Lions with big sexes, reasoning that if the mane had the same. While in Tsavo, we took the bellies (from eating big meals) tended a thermoregulatory cost, males would opportunity to perform several dummy to pant more and had higher surface be hotter than females. This turned out tests and found that these males be- temperatures, suggesting that gorg- to be true, but there was a problem: haved in exactly the same way as Seren- ing also causes heat stress. Males with Males are 50 percent larger than females geti lions, appearing intimidated by dark manes are already more compro- and might be hotter just because of a longer and darker manes. And despite mised by the heat, and thus must eat greater ratio of volume to surface area. the challenges of unfamiliar surround- smaller meals when temperatures rise. Unable to solve this conundrum in the ings, thick obscuring brush and the lack Once we had linked individual mane Serengeti, we traveled to Tsavo Na- of radio collars (which aid tracking), we phenotypes to heat stress, we revisited tional Park in Kenya, where male lions took many thermal images. What we some long-term data to see if similar were reportedly “maneless.” Tailed by a found was that Tsavo males, despite effects existed at the population level. crew from National Geographic, we took being bigger than Tsavo females, were We wondered whether mane character- a month-long detour in search of males no hotter. Thus, we concluded that the istics varied with small-scale changes that lacked manes but retained the size temperature difference between males in habitat or with seasonal differences advantage over females. If Tsavo males and females in the Serengeti derived in ambient temperature. The answer and females showed different tempera- from the heat cost of the mane rather was yes to both questions. Males born tures, then we could infer that lion tem- than that of a larger body. into prides in the Serengeti woodlands, perature was a function of size. But if the Back in the Serengeti, we next com- the warmest habitat in our study area, sexes had similar surface temperatures pared males’ body temperatures to had shorter manes throughout life re- in Tsavo, then the difference in tempera- their mane scores to find precisely gardless of the climate they lived in as ture seen in Serengeti lions must be a which mane characteristics were in- adults. Similarly, males that reached result of their manes. fluential. Mane length had little ef- adolescence in warmer-than-average We discovered that many of Tsavo’s fect, but males with darker manes years maintained shorter manes over adult males did have extremely small were significantly hotter than those the course of their lives regardless of manes, although not all were maneless. with lighter manes, even after control- their residence as adults. Finally, males

234 American Scientist, Volume 93 © 2005 Sigma Xi, The Scientific Research Society. Reproduction with permission only. Contact [email protected]. from the Ngorongoro Crater, the coolest negatively affect industries such as tour- Bibliography part of our study area, had significantly ism and legal sport hunting. Darwin, C. 1871. The Descent of Man and Selec- darker manes. These results emphasize More important is the result of such a tion in Relation to Sex. London: J. Murray. the importance of heat for determin- change on the lions. In the evolutionary Schaller, G. B. 1972. The Serengeti Lion: A Study ing mane traits and for the species in past, climate change may have driven of Predator-Prey Relations. Chicago: Chicago University Press. general: Such sensitivity to the negative to extinction species with sexually se- Selous, F. C. 1908. African Nature Notes and consequences of hyperthermia argues lected traits they could no longer afford. Reminiscences. London: Macmillan. that lions may be living at the edge of Although the mane’s phenotypic plas- West, P. M., and C. Packer. 2002. Sexual selec- their tolerance for heat. This possibility ticity makes this scenario unlikely in li- tion, temperature and the lion’s mane. Sci- raises an interesting conservation issue. ons, certain behavioral or physiological ence 297:1339–1343. Global warming is real, and as re- adaptations could become necessary. search continues to uncover the negative Such changes are impossible to predict, effects of climate change on wildlife, an but any effects on a keystone predator For relevant Web links, consult this exquisite sensitivity to heat takes on an like the lion have the potential to influ- issue of American Scientist Online: importance that is more than academic. ence whole ecosystems. Our research Broadly speaking, we predict that the emphasizes the potential consequences http://www.americanscientist.org/ continued rise in average temperatures of climate change and argues for the IssueTOC/issue/721 in East Africa will lead to fewer lions importance of behavioral studies to de- with long, dark manes. This shift may tect its more subtle effects.