image: A new study to be published in the Journal of Mammalogy examines mane variation for lions in zoos across the United States, from as far north as Chicago to as far south as Houston, where this impressive lion lives at the Houston Zoo. Bruce Patterson, PhD, the MacArthur curator of mammals at The Field Museum, visited these and other zoos last spring to photograph lions for later analysis and comparison. view more
Credit: Photo by Bruce D. Patterson, courtesy of The Field Museum
It's long been known that lions with long, full manes get the girls. Now, an innovative study based on zoo animals all across America shows for the first time that cold temperatures help the king of the beast grow his mane long and thick – and more appealing to potential mates.
In fact, up to one-half of the length and density of a zoo lion's mane can be attributed to temperature, rather than nutrition, social factors, individual history, or genes, according to a study that will be the cover story of the April issue of the Journal of Mammalogy. That journal will be published on April 13, 2006.
Dense manes retard heat loss as would a scarf or fur hat. Zoo lions in hot climates adapt with smaller, thinner manes. Those in northern zoos never overheat so no reduction in their mane is necessary. Those in southern zoos occasionally overheat, so a differential hair growth rate keeps their manes relatively thinner.
These differences in mane conditions are not the result of natural selection. Rather, they are a sign of a flexible trait that can vary to match local conditions.
Like a buck's antlers or a peacock's tail feathers, the lion's mane primarily serves to attract females and intimidate male competitors. But it comes with a cost: a full mane takes energy to grow and maintain; gives away location to prey; makes maneuvering through bramble difficult; harbors parasites, and, as we have said, retains heat. Overheating explains why lions in colder climates have longer, thicker manes: the heat-retention cost of a full mane is less for lions in cold weather conditions than it is for lions in hot weather conditions.
"While a big mane impresses everybody, even a small mane can be imposing in hot dry climates, where the costs of overheating are great and most male lions have little or no mane. This is the case in Tsavo, Kenya, where most lions are maneless," said Bruce D. Patterson, PhD, the MacArthur curator of mammals at The Field Museum and lead author of the research.
He and his colleagues began studying manes due to their research on the infamous maneless Tsavo lions. Dr. Patterson is the author of The Lions of Tsavo (McGraw Hill, 2004), which tells the story of the man-eaters. At the end of the 19h century, two Tsavo lions set upon railway crews and ate as many as 135 people (by some accounts) before they were finally hunted down and killed.
Those two lions have been on display at The Field Museum since 1925, and are the subject of a major motion picture staring Michael Douglas and Val Kilmer called "The Ghost and the Darkness" (Paramount, 1996). While their man-eating habits have garnered most of the headlines, the maneless condition of these adult male lions is even more curious.
Broad, far reaching research
The new study examined mane variation for 19 lions in 17 zoos across the United States, from as far north as Chicago to as far south as Houston. Dr. Patterson visited these and other zoos last spring to inspect lions and photograph their manes for later analysis and comparison.
His team identified 11 mane fields: throat, forehead, upper neck, sideburns, chest, shoulders, sternum, ribs, belly, elbows and dorsal crest. Dr. Patterson photographed all of these fields for each lion. Later, trained volunteers used the high-resolution photographs to rank the length, density and color of all 11 fields for each lion. The lions ranged from 1.7 to 18 years old, but age did not turn out to be a factor in mane length or density.
The zoos included in the study are located in cities that span 12 degrees of latitude or more than 2,000 miles: Alexandria, La.; Coal Valley, Ill.; Dallas; Des Moines, Iowa; Houston; Lufkin, Texas; Memphis, Tenn.; Monroe, La.; New Orleans; Oakland, Calif.; Peoria, Ill.; Sacramento, Calif.; Salina, Kan; St. Louis; Topeka, Kan.; Tyler, Texas; and Vallejo, Calif.
Mean temperatures there varied from 20 to 54 degrees Fahrenheit in January and from 65 to 87 degrees Fahrenheit in July. Cold January temperatures showed a stronger correlation with mane variation than did hot July temperatures, suggesting a stronger response to cold than to heat.
The volunteers who ranked the lion manes for length, density and color were experienced with observing lions. Most of them had studied lions in Kenya as Earthwatch Institute volunteers. Earthwatch engages people worldwide in scientific field research and education to promote the understanding and action necessary for a sustainable environment. It offers 130 expeditions in 47 countries per year (see www.earthwatch.org). "To date, 300 volunteers from 20 nations have contributed to our work in Tsavo," Patterson said. Shaking up the lion family tree
Based on the results of this study, scientists now know that lion manes can vary tremendously due to local climate. Therefore, taxonomists may be obliged to reanalyze the lion family tree.
Over the years, scientists have ascribed lions to various species and subspecies based largely on their outward appearance, especially the length and density of their manes. In fact, 23 different names have been proposed for African Panthera leo. But the new research suggests this number may be exaggerated, an idea that is supported by recent genetic studies.
"It is reasonable to hypothesize that most regional variation in manes reflects climate and other environmental influences, such as rainfall, rather than demarcating evolutionarily significant units within Panthera leo," the authors conclude.
Another result from this study will be the need for scientists to re-examine their understanding of the cave lions of Europe's Ice Age. Pleistocene lions apparently had no manes, which resulted in them being classified as separate subspecies of Panthera leo: either P. leo spelaea or P. leo atrox. But given the new knowledge that cold climate tends to increase mane length and density, the complete lack of manes in the cold Ice Age habitats "could be marshaled to justify their allocation to separate species," the authors conclude.
Lions once roamed over most of the world but are now limited to small parts of Africa and India. Only about 25,000 lions live in the wild today, down from more than 100,000 only 25 years ago. Their numbers have been decimated by human encroachment on their habitats and by conflicts with people.
"The large-maned lion has always been an important symbol to our culture," said Roland Kays, curator of mammals at the New York State Museum in Albany, N.Y., and a coauthor of this study. "We hope they can survive outside of cold-weather zoos."
The other coauthors of the study are S.M. Kasiki, of the Kenya Wildlife Service, in Nairobi, Kenya; and V.M. Sebestyen of the U.S. Census Bureau in Washington, D.C.
Lions at the following zoos were included in the results of this research: Alexandria Zoological Park, Alexandria, La.; Niabi Zoo, Coal Valley, Ill.; Dallas Zoo, Dallas, Texas; Blank Park Zoo, Des Moines, Iowa; Houston Zoo, Houston, Texas; Ellen Trout Zoo, Lufkin, Texas; Memphis Zoo, Memphis, Tenn.; Louisiana Purchase Gardens and Zoo, Monroe, La.; Freeport-McMoran Audubon Species Survival Center, New Orleans, La.; Oakland Zoo, Oakland, Calif.; Glen Oaks Zoo, Peoria, Ill.; Sacramento Zoo, Sacramento, Calif.; Rolling Hills Zoo, Salina, Kan.; Saint Louis Zoological Park, St.Louis, Mo.; Topeka Zoological Park, Topeka, Kan.; Caldwell Zoo, Tyler, Texas; Marine World, Vallejo, Calif.
In addition, the following zoos were involved in the study even though lions their lions were not included in the final comparative analysis: Lincoln Park Zoological Gardens, Chicago, Ill.; Fort Worth Zoological Park, Ft. Worth, Texas; Kansas City Zoo, Kansas City, Mo.; San Francisco Zoological Gardens, San Francisco, Calif.; Sedgwick County Zoo, Wichita, Kan.
Great digital images of lions available by email:
1.) Kansas lion with full mane does not look cowardly!
Long, thick manes such as this one intimidate rivals and attract potential mates. But they come with a cost, including heat retention. New research shows that lions adapt to hotter climates by growing manes that are less long and thick. This lion lives at the relatively northern Topeka Zoological Park in Topeka, Kansas. Therefore it has a bigger, denser mane than other lions in the study that live in relatively hotter southern climates.
Photo by Bruce D. Patterson, Courtesy of The Field Museum
2.) New research explains variation in manes
A new study to be published in the Journal of Mammalogy examines mane variation for lions in zoos across the United States, from as far north as Chicago to as far south as Houston, where this impressive lion lives at the Houston Zoo. Bruce Patterson, PhD, the MacArthur curator of mammals at The Field Museum, visited these and other zoos last spring to photograph lions for later analysis and comparison.
Photo by Bruce D. Patterson, Courtesy of The Field Museum
3.) King of the beast soaks up some sun
This lion lives in the Alexandria Zoological Park in Alexandria, La. The new research helps explain the correlation between climate and manes and may lead to revisions in the lion's family tree. For example, maneless Ice Age lions were once thought to be a separate subspecies of the African lion, aka Panthera leo. But now scientists know that P. leo retains longer, denser manes in colder climates, so they may determine that the Ice Age maneless lion was a completely different species than P. leo.
Photo by Bruce D. Patterson, Courtesy of The Field Museum
4.) The mane story
Manes cover more of the lion's body than just the head and neck. For this study, researchers identified 11 mane fields: throat, forehead, upper neck, sideburns, chest, shoulders, sternum, ribs, belly, elbows and dorsal crest. They compared the length and density of these 11 mane fields for all 19 lions. These lions live at the Caldwell Zoo in Tyler, Texas.
Photo by Bruce D. Patterson, Courtesy of The Field Museum
5.) Tsavo Lion in the wilds of Kenya
Cassius, this seven-year-old maneless male lion from the Tsavo National Park in Kenya, will grace the cover of the April issue of the Journal of Mammalogy. He was not part of the study discussed here, which was restricted to zoo lions in the United States. Nevertheless, Cassius' sparse mane suggests that a hot climate might contribute to shorter, less dense manes – even outside of zoos. "Many variables interact to affect mane development in wild lions, like this one from Rukinga Ranches near Tsavo National Park," said Bruce D. Patterson, PhD, the MacArthur curator of mammals at The Field Museum and lead author of the research. "Several of these variables, including food, water, and social groupings are controlled in zoological parks, where the authors show climate has a major effect on mane development."
Photo by Bruce D. Patterson, Courtesy of The Field Museum
Journal
Journal of Mammalogy