Big Cajones: Testicle Size Determines Speed Of Genome Evolution

By Shweta Iyer on March 6, 2014 1:17 PM EST

gorilla
A universal truth among primates is this - the bigger the balls, the faster the evolution. (Photo: Photo courtesy of Shutterstock)

A universal truth among primates is this - the bigger the balls, the faster the evolution.  After studying the correlation between testicles weights and increased sperm production, author Alex Wong has published his results in advanced online edition of Molecular Biology and Evolution, which states that big testicles are needed for genetic evolution, according to a press release Wednesday.

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In many primates, females mate with multiple partners. This leads to intense competition among males of the species to pass along their sperm and ensure proliferation of their DNA. Alex Wong used DNA sequence sets of 55 species of primates to test for a correlation between substitution rates that is change in the characteristics of cellular molecules such as DNA or RNA and the weight of the testes in these primates.

The widely accepted belief is that more rounds of cell division in the testicles results in production of more sperm. Increased rounds of cell division results in more mutations, which in turn leads to higher genetic evolution."In general, the speed of genome evolution is higher for species in which males have large testes in comparison to species in which males have small testes," said Wong. "This finding helps us to understand why genomes evolve at different rates in different species, and has implications for our understanding of the relationship between female mate choice and the overall fitness of a population."

Wong applied sophisticated evolutionary methods to find a correlation between testicle size and substitution rates in primates. His findings gave proof of a positive correlation between them. These findings also support the theory that competition between males in species where the female mates with more than one male, results in higher spermatogenic activity (increase in production of sperms) and consequently higher substitution or genetic mutation in the sperms.

"The current finding of covariance between sperm competition intensity and substitution rates adds to a growing body of knowledge concerning the sources of substitution rate variation," said Wong. "The extent to which this covariance is widespread is not yet clear; application of robust comparative methods to large phylogenetic datasets in other taxa, such as birds and insects, will help to establish its generality."

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