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 lions grow their manes long and thick - and more appealing to potential mates.
Up to one-half of the length and density of a zoo lion's mane can be attributed to temperature, according to a study that is the cover story of the April issue of the Journal of Mammalogy, published on April 13, 2006. Other factors involved in mane growth include nutrition, social factors, individual history, and genetics.
"Many variables interact to affect mane development in wild lions," said Dr. Bruce Patterson, MacArthur curator of mammals at The Field Museum i and lead author of the research. Patterson is principal investigator of Earthwatch's Lions of Tsavo project. "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."
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 their location away to prey, makes maneuvering through bramble difficult, harbors parasites, and, as this study illustrates, retains heat.
Dense manes retard heat loss as would a scarf or fur hat. 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, but rather indicate a flexible trait that can vary to match local 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," said Patterson. "This is the case in Tsavo, Kenya, where most lions are maneless."
Earthwatch teams are helping Patterson and colleagues study the maneless lions of Tsavo, which inspired the authors' interest in the factors in mane growth. Patterson is the author of The Lions of Tsavo, the story of the two notorious lions that ate as many as 135 people (by some accounts) in the end of the 19th century, before they were finally hunted down and killed.
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. Patterson visited these and other zoos last spring to inspect lions and photograph their manes for later analysis and comparison. Trained volunteers, many of them with experience from Earthwatch's Lions of Tsavo project, used the high-resolution photographs to rank the length, density, and color each lion's main, using specific criteria. 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. 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.
Based on the results of this study, scientists now know that lion manes can vary tremendously due to local climate, which may call for a reanalysis of 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 the African lion, 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.
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., a coauthor of this study, and co-principal investigator of Earthwatch's Lions of Tsavo project. "We hope they can survive outside of cold-weather zoos."