Howler Monkeys With Loud Manly Calls Are Not As Well Endowed, Study Finds (VIDEO)
Scientists discovered an evolutionary trade-off between howler monkeys' vocal organs and sexual organs.
By Rebekah Marcarelli
r.marcarelli@hngn.com | Oct 23, 2015 01:34 PM EDT
Howler monkeys are one of the loudest animals on Earth, but new research suggests those with the most impressive are actually overcompensating for something.
A recent study found the male howler monkeys with the loudest calls had smaller testes and produced less sperm than their quieter peers, the University of Cambridge reported. This evolutionary "trade-off" between the size of the male hyoid (the hollow throat bone that allows the guttural call to resonate), and the size of the reproductive organs corresponds with the mating systems of different howler species. The researchers found males with large hyoids and small testes generally lived in small social groups in which one male dominated many females; howlers with small hyoids and large testes lived in groups of five to six males in which the females mated with all of the males in the social circle. Since males in the latter group do not have exclusive access to females, they must rely on "sperm competition," where quality and quantity is key for insemination.
...
