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."

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