|
 Howler monkeys make among the loudest, deepest sounds of any land
animal, and males use their roars to attract the ladies for mating
and intimidate other males.
But scientists on Thursday said they have discovered a curious
paradox: males that make the lowest-frequency calls considered the
most alluring to potential mates are endowed with the lowest
reproductive potential.
The research focused on a cup-shaped bone, the hyoid, located above
the larynx that creates a resonating chamber to amplify
vocalizations.
Among nine howler monkey species studied, those with the biggest
hyoid produced the deepest and lowest-frequency calls, but also had
the littlest testes for sperm production.
"We discovered that the largest hyoid bones were found in howler
monkey species with the smallest testes volume, and vice versa,"
University of Utah anthropologist Leslie Knapp said.
 University of Cambridge biological anthropologist Jacob Dunn called
it an "evolutionary trade-off" for male howler monkeys between vocal
tract and testes size.
"This means that different species of howler monkeys either invest
in one of these traits or the other, but not both," Dunn said. "I
think the main message is that when it comes to reproduction, you
can't have everything."
Howler monkeys, found from southern Mexico to Argentina, spend most
of their time in tall trees with the help of their gripping,
prehensile tails, munching leaves, fruits and flowers. Their howls
can be heard 3 miles (5 km) away.
[to top of second column] |
"Howls sound a bit like the roar of a lion, but many howlers produce
even deeper and more complex sound," Knapp said. "Deeper howls
suggest large body size, so howlers with deep howls give the
impression that they are bigger than they really are. This is an
advantage for males that are competing to mate with females."
Males in species that live in "harem" groups of one male and
multiple females have a very large vocal tract but small testes.
Males in species with multiple males and females per group have
smaller vocal tracts but larger testes.
"This is probably because the females in these species will mate
with several males, and so the males have evolved to produce more
sperm to increase their chances of fertilizing an egg," Dunn said.
The research appears in the journal Current Biology.
(Reporting by Will Dunham; Editing by Sandra Maler)
[© 2015 Thomson Reuters. All rights
reserved.]
Copyright 2015 Reuters. All rights reserved. This material may not be published,
broadcast, rewritten or redistributed.
 |
