The mane thing about lions
The lion's mane is indeed all for show - new research shows that lionesses go for dark-maned lions and males tend to avoid their darker and longer-haired opponents - and it's all got to do with testosterone.
Published in the current issue of Science Magazine, the research shows that the evolution of the lion's mane is due largely to reproductive benefits.
Combining their results from field experiments, with analysis of demographic data, Ms. Peyton West and Professor Craig Packer, at the University of Minnesota, show males with manes are able to intimidate rivals, while males with dark manes are better able to attract females.
"Some people have suggested the mane's evolution was initially due to its ability to protect the neck in fights, but our data suggests this is not a significant factor," said Ms. West.
The scientists travelled to Serengeti National Park, Tanzania, and Tsavo East National Park, Kenya, where they tested the response of males and females to differences in mane size and length.
The researchers used life-sized "model" lions made specially for them by a Dutch toy company. After positioning the models a recording of scavenging hyenas - a dinner bell for lions - was played to attract real lions to the area. The scientists were then able to trial four different mane (wig) types: long and dark, long and blonde, short and dark and short and blonde.
By swapping these around, they determined females prefer males with darker manes while males tend to avoid their darker and longer-haired opponents. They found there are good reasons for this.
Statistical analyses to compare the mane scores of 68 male lions with their testosterone levels show males with darker manes have higher testosterone.
Not only that, the darkness of a lion's mane is a reliable indicator of his nutrition level, measured by comparing "belly sizes" of dark and light maned males.
"During the cooler months of the year, darker maned males had bigger bellies than light maned males. In the warmer months belly sizes were the same. This means overall males with darker manes have higher food intake," said Ms. West.
Given that testosterone is associated with aggression, darker maned males are likely to be more aggressive opponents. And since they are also better fed, they are in better fighting condition.
"When inspecting a stranger, males hope to avoid fighting if they possibly can since even a successful fight can result in serious injury. As a result, they will steer clear of the male most likely to escalate an encounter into an actual fight," explained Ms. West.
"Females, on the other hand, will seek to mate with the fittest males, to obtain better genes for her offspring, and protection from other males."