Researchers Find Biggest Sex Organs in Animal Kingdom

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A species of cricket has broken an unlikely world record: It has the largest testicles in relation to its body weight.

The Tuberous bushcricket's testicles account for 14 percent of its body weight. To put that in perspective, the testicles of a man weighing 200 pounds (91 kilograms) with that ball-to-body ratio would weigh 28 pounds (12.7 kg). [Image of cricket and its testicles]

The bushcricket, whose anatomical extremes are reported today (Nov. 9) in the journal Biology Letters, edges out the record of a species of fruit fly, Drosophila bifurca, whose testes to body weight ratio has been recorded as 10.6 percent. And lead researcher Karim Vahed, Reader in Behavioural Ecology at the University of Derby, confessed that he was stunned by the size of the creature's gonads.

"We couldn't believe the size of these organs -- they seemed to fill the entire abdomen," he said.

Vahed told that he didn't set out on a hunt for the creature with the biggest sex organs -- that finding was simply a lucky break.

"We set out to test various hypotheses about the selective pressures responsible for variation in testes size," Vahed said, "and just happened upon the largest as a percentage of male body mass."

Oddly enough, the researchers report, the cricket's large testicles don't produce greater volumes of semen per ejaculate. In fact, they produced less voluminous sperm than smaller testicles.

"Traditionally it has been pretty safe to assume that when females are promiscuous, males use monstrously-sized testicles to deliver huge numbers of sperm to swamp the competition -- even in primates," study researcher James Gilbert of the University of Cambridge said in a statement. "Our study shows that we have to rethink this assumption. It looks as though the testes may be that big simply to allow males to mate repeatedly without their sperm reserves being exhausted."

The Tuberous bushcricket joins a veritable Who's-Who list of animals with strange genitalia, including:

* Single-testicled carabid beetles
* Rodents that enjoy a mating advantage thanks to their long penises
* Polar bears whose penises are shrinking because of pollutants
* Ducks with penises like corkscrews (and vaginas to match)
* Smart bats with small testicles

And to round out the list, some male fruit bats (Rousettus aegyptiacus) have testes that are 2.15 percent of their body mass, whereas their brains are only 1.70 percent. [See the male fruit bat's genitalia]

* Why So Many Animals Evolved to Masturbate

* Top 10 Swingers of the Animal Kingdom

* Q&A: Discoverer of Dead Gay Duck Sex contributed to this report.