Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Researchers find three major beetle groups coming up one testicle short

07.03.2005


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.



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 researchers noted that except for this one anatomical distinction, the one-testicle beetles appear and behave no differently than their two-testicle counterparts.

"The beetles with one testis are mating normally and doing their beetle thing," said James Liebherr, professor of entomology at Cornell University. "It strikes me that carabid beetles are pretty well known to scientists, yet the loss of an entire organ across three major lineages was not fully comprehended until this study."

For reasons unknown, in almost all cases it is the left testis that has disappeared. "You might say that these beetles lost all that was left, except for one small group that seems to have lost their right," quipped Will, who is also associate director of UC Berkeley’s Essig Museum of Entomology. While animals such as jellyfish and starfish are radially symmetrical, bilateral symmetry is, hands down, the dominant body shape in the animal world, thanks in part to the drive for forward motion.

That’s not to say there is no precedent for such deviations from bilateralism. One well-known example is the male fiddler crab, which has an outsized claw on one side that is used to attract female crabs and fend off male competitors.

Still, the researchers said the complete absence of an organ, or absence asymmetry, is rare. When it does occur, there is likely a good reason for the organ loss. Snakes, for example, have one lung that is significantly reduced to accommodate a relatively extreme body shape. Most birds have only one functioning ovary, which some biologists believe helps optimize their bodies for flight. That raises the question of how and why some beetles evolved to have just one testis. The researchers ruled out obvious factors such as flight advantages or major changes in body form.

They did notice that the monorchid beetles’ accessory glands, which produce the bulk of the seminal fluid, were somewhat larger than normal. The researchers suggest that packing of the internal organs in the abdomen is a kind of competition for space that may lead to the loss of the functionally redundant testis. "Male crickets will directly transfer fluid from their accessory glands to female crickets to provide nutrition to their eggs," said Liebherr. "It may be that the male beetles are similarly providing other things than sperm to the females. But it’s a chicken and egg question. We don’t know what came first. Was the testis lost first, leaving more space for the accessory glands to grow? Or did the testis lose out to make way for a larger accessory gland? That’s a subject for further study."

Whatever the ultimate cause, something drove the evolution of this absence asymmetry. "We found monorchy in three distantly related groups of carabid beetles - Abacetini, Harpalini and Platynini - indicating that the loss of the testis occurred at least three separate times in the evolution of the beetles," said Will. "It seems unlikely that it was completely random."

Based on the geographic distributions of the beetle groups involved, Liebherr estimates that the origins of monorchy in the beetles occurred 90 to 100 million years ago during the Cretaceous period. "That era witnessed a dramatic increase in the diversity of organisms," he said. He added that these findings illustrate the value of basic natural history. "So many of the scientific discoveries today seem to occur primarily on the molecular and genetic level, so findings such as this are remarkable," said Liebherr. "A lot of the ideas that come to the lab bench start in the field. We still have much to discover by looking at whole organisms."

Other co-authors are David Maddison at the University of Arizona and José Galián at the Departamento de Biología Animal Facultad de Veterinaria in Murcia, Spain.

This research was funded by the National Science Foundation.

Sarah Yang | EurekAlert!
Further information:
http://www.berkeley.edu

More articles from Life Sciences:

nachricht Cells communicate in a dynamic code
19.02.2018 | California Institute of Technology

nachricht Studying mitosis' structure to understand the inside of cancer cells
19.02.2018 | Biophysical Society

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: In best circles: First integrated circuit from self-assembled polymer

For the first time, a team of researchers at the Max-Planck Institute (MPI) for Polymer Research in Mainz, Germany, has succeeded in making an integrated circuit (IC) from just a monolayer of a semiconducting polymer via a bottom-up, self-assembly approach.

In the self-assembly process, the semiconducting polymer arranges itself into an ordered monolayer in a transistor. The transistors are binary switches used...

Im Focus: Demonstration of a single molecule piezoelectric effect

Breakthrough provides a new concept of the design of molecular motors, sensors and electricity generators at nanoscale

Researchers from the Institute of Organic Chemistry and Biochemistry of the CAS (IOCB Prague), Institute of Physics of the CAS (IP CAS) and Palacký University...

Im Focus: Hybrid optics bring color imaging using ultrathin metalenses into focus

For photographers and scientists, lenses are lifesavers. They reflect and refract light, making possible the imaging systems that drive discovery through the microscope and preserve history through cameras.

But today's glass-based lenses are bulky and resist miniaturization. Next-generation technologies, such as ultrathin cameras or tiny microscopes, require...

Im Focus: Stem cell divisions in the adult brain seen for the first time

Scientists from the University of Zurich have succeeded for the first time in tracking individual stem cells and their neuronal progeny over months within the intact adult brain. This study sheds light on how new neurons are produced throughout life.

The generation of new nerve cells was once thought to taper off at the end of embryonic development. However, recent research has shown that the adult brain...

Im Focus: Interference as a new method for cooling quantum devices

Theoretical physicists propose to use negative interference to control heat flow in quantum devices. Study published in Physical Review Letters

Quantum computer parts are sensitive and need to be cooled to very low temperatures. Their tiny size makes them particularly susceptible to a temperature...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

2nd International Conference on High Temperature Shape Memory Alloys (HTSMAs)

15.02.2018 | Event News

Aachen DC Grid Summit 2018

13.02.2018 | Event News

How Global Climate Policy Can Learn from the Energy Transition

12.02.2018 | Event News

 
Latest News

Contacting the molecular world through graphene nanoribbons

19.02.2018 | Materials Sciences

When Proteins Shake Hands

19.02.2018 | Materials Sciences

Cells communicate in a dynamic code

19.02.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>