November 10, 2010

Bushcricket Has World’s Largest Testicles

British university scientists have discovered a species of bushcricket that boasts the largest testicles in the animal kingdom, representing 14 percent of their total body weight, according to a new study published Wednesday in the journal Biology Letters.

In the study, biologists at the University of Derby and the University of Cambridge noted that the sizable testes of the Tuberous Bushcricket (Platycleis affinis)--the largest in relation to body weight in the world--point towards rampant promiscuity among members of the species.

"We couldn't believe the size of these organs, they seemed to fill the entire abdomen," head researcher Dr. Karim Vahed, a behavioral ecologist with the University of Derby, said in a statement. "An almost universal evolutionary rule appears to be that such variation in relative testes size is linked to female mating behavior; testes tend to be larger in species where females are more promiscuous."

"But at least two hypotheses could account for this pattern--sperm competition on the one hand and male mating rate on the other," Dr. Vahed added. "Yet our study appears to be the first study to show that, in the case of the Tuberous Bushcricket, bigger testes don't necessarily produce more sperm per ejaculate."

During their research, the investigators compared the testicle size of the Platycleis affinis with more than 20 other types of bushcricket. They discovered that the larger testes were most common in species where females mated with multiple males, and in the case of the Tuberous bushcrickets, one female can have up to 23 different partners during their two-month adult lifespan, they report.

"This strongly suggests that extra large testes in bushcrickets allow males to transfer relatively small ejaculates to a greater number of females," said Dr. Vahed.

To put their findings into perspective: according to a Wednesday article by the AFP, a human male would have to have 22-pound testicles to compare to the Tuberous Bushcricket. Prior to this study, the species that had been recognized as possessing the largest testes in relation to body weight was the Drosophila bifurca, a fruit fly whose testicles comprise 10.6 percent of its total mass.


Image 1: Dr Karim Vahed holding a specimen of a male Tuberous bushcricket together with its testicles. Credit: University of Derby

Image 2: A Tuberous Bushcricket (Platycleis affinis). Credit: University of Derby


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