Image copyright Reuters deep and menacing roar of howler monkeys may indicate their reproductive weaknesses, say biologists.
The study of the international team of scientists found that primates develop any loud voices or large testicles, but both at the same time does not happen.
Scientists say that such evolutionary trade-offs may be more common than previously thought.
howler got their name because of their inherent energetic, menacing roar. These sounds of animals trying to intimidate rivals and to please prospective mates.
Their anatomical musical instrument – a bone in the throat, which serves as a resonator.
The vocal cords of animals act as a string instrument, and hyoid bone – how the instrument itself. Its size is directly related to the depth of the roar.
“The deeper roar, so it seems to be more attractive to females,” – explained the head of the research team, Jake Dunn of Cambridge University.
The results are published in the journal Current Biology.
hyoid bone
Looking at different kinds of howlers, scientists noticed that the hyoid bone in them is very different size.
“The dimensions of the largest in the 14 times the minimum – said Jake Dunn. – We are really interested in why this feature has so many wonderful variations”.
Together with colleagues from the University of Utah researchers conducted a laser scan of more than 200 hyoid howler from museums in the United States and Europe.
In addition to the variation of size this bone, they noticed a relationship with another striking difference in the structure of the body of primates.
“The difference in the amount of monkey testicles are also very important. The largest is 6.5 times as massive as the youngest “- Jake Dunn says.
compromise
Comparing animals, Jake Dunn and his team found that different kinds of howlers, it seems, are looking for a compromise between the development of powerful vocal tract needed to play lower and impressive music, or the development of large testicles – for more sperm.
According to him, depending on the mating in its group different primates choose which of these signs develop.
Jake Dunn explains that some animals – such as walruses, seals and sea lions – especially large sizes have smaller genitalia.
In 2012, it was even published study suggests that a man with a deep voice, have fewer sperm left.
But the results of studying howler is the first recorded example of a compromise between the vocal and the production of sperm of all kinds.
“It was a surprise – to find out that such trade-offs may be more common than previously thought,” – said Jake Dunn.
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