Males of some species develop bigger testes for competitive edge

Washington, Mar 24 (ANI): In species where competition for females is fierce, males have evolved bigger testes to beat their rivals, a new study has confirmed.

The study showed that testicle size matters in highly competitive animal societies, where females mate with many males or in which females live in groups ruled by an alpha male that must constantly defend his harem.

However, the females do not really seek out more endowed males. Instead, the rivalry occurs after mating, as sperm battle inside the female.

As expected, males with larger testes produce more sperm.

Males are generally known to have developed tricks for edging out their challengers, such as displaying brighter plumage-often seen in birds-or wooing females with gifts.

Testes size is part of this competition, according to study leader Carl Soulsbury, a biologist at the University of Bristol in the U.K.

Soulsbury said that evidence has also been found that within species, the biggest, most attractive, and healthiest males have the heftiest testes, which indicates that the two might have a link.

Previous studies had looked at testes size and mating behaviour, which could be unreliable, said Soulsbury.

Thus, he examined previously published data on several wild mammal species that used genetic testing to prove that litters of offspring had been sired by many males, or, in group-living species, that offspring had been sired by a single dominant male.

Then he used data on testes mass-as well as other factors, such as length of mating season-to develop a statistical model.

The model revealed that "where there's a high competition between males, evolution has selected for larger testes," said Soulsbury.

"It confirms what scientists have expected, but is the first to prove it using genetic data across a range of mammals," National Geographic News quoted him as saying.

Men do not compete in the same way for women, meaning that their testes stay relatively small.

The study has been published in the journal PLoS ONE. (ANI)