How Monkeys Make Up for Their Size

The post Tiny But Mighty: How Monkeys Compensate for Their Size appeared first on AZ Animals.

Quick shot

• this The “big car, little man” phenomenon Also found in the animal kingdom.

• this loudest Howler monkeys were found to have Minimal package.

• hyoid bone size, responsible for vocalization, and testicle size.

• Such strategies honest exaggeration For howler monkeys, it is very effective in ensuring reproduction.

If you lose your vision, you can compensate with your other senses. If one arm is amputated, you learn to do twice as much with the other arm. The balancing act continues, juggling and shuffling to reach some average. But loss of limbs and senses aren’t the only things people feel they have to compensate for; we’re all familiar with the “big truck, small person” phenomenon. Humans are not the only species that instinctively overcompensates. In fact, research shows that the monkeys that scream and howl the loudest tend to have the smallest packages.

We don’t mean gifts either. The monkeys that felt the need to shout out to everyone in the jungle seemed to do so for compensatory reasons: the louder the screams, the smaller the testicles and the lower the sperm count. However, this squealing index is not entirely behavioral compensation for a lack of dominance. Monkeys with smaller testicles but loud calls were just as fertile as quieter monkeys. Let’s learn more about this fascinating study and what it explains about the dynamics of relationships between competitive male howler monkeys.

howler monkey music

Howler monkeys are one of the few monkeys that build nests. As the name attests, they are also one of the loudest animals on Earth. Black howler monkeys, for example, are so loud that their calls can reach 100 decibels and can be heard up to three miles away. By comparison, the sound of a jet engine can rupture an eardrum at 150 decibels. These powerful vocalizations play an integral role in howler monkeys’ social dynamics, but scientists wanted to understand exactly how.

This resulted in the landmark 2015 study “Evolutionary trade-offs between vocal cords and testicle size in howler monkeys,” led by Dr. Jacob Dunn of the University of Cambridge and published in the journal modern biology. Research shows that howler monkeys, the loudest and most impressive of all, produce far fewer sperm than their counterparts. Now, a follow-up study illustrates how the acoustic properties of howler monkeys’ roars, specifically formant spacing, can be a reliable indicator of body size.

hyoid business

The correlation between howler monkeys’ call power and testicle size is humorously called the “call-and-balls” trade-off. However, this compensatory survival strategy depends on the hyoid bone.

The hyoid bone is found in the neck of animals and supports their tongue. The human hyoid bone is horseshoe-shaped. However, howler monkeys’ hyoid bones have become larger through evolution. These large hyoid bones are cup-shaped and amplify their howls. Several studies, including a recent one, have shown that the size of the hyoid bone in howler monkeys is inversely related to testicular size, suggesting a developmental trade-off. Simply put: the bigger the hyoid bone and the louder the cry, the smaller the testicles. This correlation also works in reverse. The smaller the hyoid bone, the quieter the cry, and the larger the package.

The idea that evolution would favor smaller reproductive organs in exchange for louder calls seems counterintuitive. That is, until you take a closer look at the social dynamics of different howler monkey species. Some animals compete before mating, while others compete after mating. The reproductive strategy of an individual howler monkey depends on the size of its hyoid bone.

reproductive trade-off

Researchers from the University of Utah and the University of Cambridge have shown that howler monkeys adopt different reproductive methods depending on their attributes. Monkeys with large mouths and small balls usually live in groups consisting of one or two males and more females. They use loud and terrifying roars to drive away potential males. Therefore, competition is minimized. At the other end of the howler monkey spectrum are the quieter males. These males with smaller hyoid bones live in large mixed groups. Since they have to compete with more males for the same female, evolution puts all their energy into testicle size. The larger the testicles, the greater the chance that sperm will reach the woman’s egg first.

effective hyperbole

Twin studies show that the hyoid bones of tiny howler monkeys contain features not found in humans. For example, these howler monkeys have a tiny band of tissue above their vocal cords. When vibrating, the membrane produces strange, non-linear sounds that can’t be ignored. As Dunn explains in an article, “The investment in developing large vocal organs and roaring may be so expensive that there simply is not enough energy to invest in testicles. Alternatively, using large vocal organs for roaring may be so effective at deterring competitors that investing in large testicles is not necessary.”

The findings have reverberated across primate research. A 2019 study titled “Trade-off between sexual ornaments but not weapons and testicle size in primates” found that across all primate species, those that invested more in sexual ornaments such as the hyoid bone and larynx tended to have smaller testicles. A hyoid bone large enough to allow a 17-pound monkey to make sounds like an adult tiger.

Surprisingly, it works. The loud shouting strategy is very successful for the males carrying the smallest packages, so they usually assemble the largest harems. Keep this in mind the next time you see someone driving an oversized truck down the road. As biologists say, a little honest exaggeration goes a long way.

The post Tiny But Mighty: How Monkeys Compensate for Their Size appeared first on AZ Animals.