Some male orangutans sport a special facial feature: cheek pads -- large folds of flesh on either side of the face. It turns out that this catcher's-mitt-with-a-face-in-the-middle look may be a key to being especially successful siring offspring.
Cheek pads are seen only on the dominant males in a given area, and researchers from the Max Planck Institute for Evolutionary Anthropology wanted to know why a dominant male would even bother developing them, when his life was tough enough already and he didn't need them to father children (subordinate males, without cheek pads, can also have perfectly good reproductive success).
"Dominant males have to find and consume more calories. Their movement is restricted as a result of their size, and fights with neighboring dominant males have been known to result in death," explained study co-author Graham L. Banes, in a press release. "So, why would a male develop cheek pads if he can father offspring without?"
To find out, Banes and co-author Linda Vigilant spent eight years gathering data on orangutans in Camp Leakey, in Indonesia's Tanjung Puting National Park. They compared the reproductive success of its dominant male of the era, Kusasi, with that of the camp's subordinate males.
The team's extensive paternity testing program, using DNA sampling of fecal matter, showed that Kusasi, he of the handsome cheek pads, was indeed a boss, fathering many more children than did the subordinate males.
The answer, then, to the researchers' question of 'why cheek pads when you don't particularly have to?' seemed to be that the feature skews things significantly enough in a cheek-padded orangutan's favor to make it worth the evolutionary effort.
And what of the poor subordinate male orangutans of Camp Leakey? Were they forever playing second fiddle to Kusasi? Not quite. The scientists found that nature opened a window of sorts for them.
"These other males were typically reproductively successful at the beginning and end of Kusasi's dominant period," said Banes, "when the hierarchy was potentially unclear."
Banes and Vigilant's findings have been published in the journal Behavioral Ecology and Sociobiology.