The discovery is striking because most animals are bilaterally symmetrical, which means the left and right sides of the body roughly mirror each other. This bilateralism extends to many internal organs, although some systems, such as the human heart and liver, develop or are positioned asymmetrically.
"We've got two lungs, two kidneys, and females and males have paired gonads. Even our brain has two hemispheres," said Kipling Will, assistant professor of insect biology at the University of California, Berkeley's College of Natural Resources. "Evolution has predominantly favored bilateral symmetry in animals, so when we see that the rule is violated, as in the case with these beetles, it gets our attention."
Will led a systematic survey of all major lineages of the beetle family Carabidae. The results of the survey will appear in the April print issue of the Journal of Morphology, but are available now online.
The researchers said that field observations such as this provide valuable clues to beetle biology and evolution.
The one-testis phenomenon, or monorchy, was first noted in beetles by French naturalist Leon Dufour in 1825. He found that Harpalini carabid beetles had a single testis, but he and other scientists considered the condition to be limited to this group. It would take another 180 years before researchers would conduct a more thorough survey, finding that two other major lineages also lack one testis.
The survey required detailed dissection and study of over 820 species, a representative sampling from the 37,000 species of carabid beetles estimated to exist. The researchers found 174 species, all members of the three lineages with only one testis. The res
Contact: Sarah Yang
University of California - Berkeley