On the left is a typical beetle (Amara) with two testes, shown from above with the top of the abdomen removed. On the right is an Onypterigia tricolor beetle that lacks the left testis. Researchers have found that monorchid (single testis) beetles are more common than previously thought. (Photos by Kipling Will, UC Berkeley)
The fact that this Onypterigia tricolor beetle is missing its left testis is not apparent from the outside. The beetle is a member of the tribe Platynini one of three beetle lineages that have only one testis instead of the typical pair.
A surprisingly large number of beetles are missing one of their testes, the male gonads of insects. As far as the researchers who discovered this can tell, the insects are not in any way bothered or impaired by this absence.
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.
Sarah Yang | EurekAlert!
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