Male proboscis monkeys’ large noses may help them attract females
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The male proboscis monkey’s strangely enlarged nose acts like a trumpet, enabling it to make extremely loud noises to attract females and intimidate rivals.
Until now, researchers had speculated that it must play a role in mating and dominance, but had no evidence of its exact purpose or function.
“No other monkey has a nose this big,” he says. katherine valoria Graduated from Australian National University, Canberra. “That nose has become a symbol of health and superiority. Women find it attractive, but men find it threatening.”
To investigate further, Balolia et al. carried out a detailed analysis of the cranial anatomy of the proboscis monkey (Nasalis larva) and compared their nasal structure with that of three other Old World monkey species: blue monkeys, king colobus monkeys, and crab-eating macaques.
The researchers found that male proboscis monkeys’ nasal cavities are 29 percent larger than females. For the other three species, the differences between sexes ranged from 7% to 15%.
Male proboscis monkeys also had 26 percent larger nasal cavities than females, compared to a difference of 7 to 17 percent in the other three primate species. Significant differences in certain physical characteristics between the sexes may indicate that sexual selection is at work.
Importantly, this nasal anatomy only reaches its full size once the male reaches sexual maturity. Up until this point, young males belong to bachelor groups and form groups with multiple females only when their snouts are fully grown. This provides evidence that this body part is important for successful mating.
Valoria said the monkeys are also known for making extremely loud calls using their noses rather than their mouths. “Due to the shape of the nasal cavity, it acts like an echo chamber,” she says. “They use their nasal cavities to increase sound and resonance, then straighten their soft tissue to use their nose like a trumpet.”
The team speculates that such distinctive noses may have evolved because loud noises were important in the dense forests where the monkeys live.
Females may have started selecting mates with larger noses because it was a sign of their own fitness and dominance, Valoria says, which would have encouraged the evolution of even larger noses.
“It’s probably like a peacock’s tail. It just keeps getting bigger and bigger and bigger until it can’t get any bigger.”
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Source: www.newscientist.com
