Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

When it comes to sperm competition, size can matter — it’s the female who holds the aces

08.11.2002


Syracuse University researchers pick up where Darwin left off: Groundbreaking study to be published in the Nov. 8 issue of Science



When it comes to mating and determining whose sperm reaches the elusive egg, females control both the playing field and the rules of the game, according to a new study on male sperm competition vs. female choice to be published in the Nov. 8 issue of Science.
"Our study demonstrates, unambiguously, the active role females play in determining the conditions under which sperm compete inside the female reproductive tract," says Scott Pitnick, professor of biology at Syracuse University, who published the study with co-researcher Gary T. Miller, a postdoctoral research associate at SU. "It’s widely known that, throughout the animal kingdom, sperm cells evolve rapidly into some of the most outrageous variations in size and shape. Until now, we didn’t know why. Our study shows that it’s because of female choice. The shape and physiology of the female reproductive tract is driving this variation in sperm."

Most people are familiar with the elaborate competitions that occur between males before mating, such as the ritualistic clash of horns of Big Horn Sheep or the bloody battles between male elephant seals. However, relatively little is understood about how sperm compete after mating has occurred, says Pitnick, an evolutionary biologist who has been studying sexual selection and the nature of sex differences for more than 15 years. In a 1995 study published in Nature, he documented the longest sperm cell known to science. It belongs to a species of fruit fly called Drosophila bifurca and measures some two inches in length when fully uncoiled.



"It was once a widely held belief that males sacrificed quality for quantity when it comes to sperm production and the competition to fertilize eggs," Pitnick says. "In 1995, we documented exceptions to the rule. That finding led us to wonder why some species take the time to produce a few gigantic sperm when the majority seem content to spew out millions of tiny sperm."

Contrary to popular belief, females in most species are promiscuous, mating with more than one male during a single mating season, Pitnick says. Females of most species also have specialized sperm-storage organs where sperm from different males compete to emerge and race for the egg. Pitnick and Miller used populations of another species of fruit fly called Drosophila melanogaster to discover the nature of the relationship between sperm size, the size of female sperm-storage organs and successful fertilization. The researchers manipulated the populations and selected groups based on the length of sperm and the length of the female sperm-storage organs.

The result: All males competed equally well within females with short sperm-storage organs, but males with longer sperm out-competed their less endowed rivals within females sporting longer storage organs. The advantage to males of longer sperm increased with increasing length of the female tract. "This means," Pitnick says, "that the length of the sperm-storage organ is a mechanism dictating female choice among potential sires of her offspring. Females choose among males based on the length of their sperm. Long sperm tails are thus the post-copulatory, cellular equivalent of long peacock tail feathers."

The researchers’ conclusion was supported in a separate experiment in which evolving female sperm-storage organs were shown to drive the evolution of sperm length.

"Now that we know about sperm-female co-evolution, it’s important to ask what happens when populations are isolated from one another," Pitnick says. "Sperm from one population may become mismatched and thus reproductively incompatible with the females of the other population. This is where the rubber meets the road for speciation. The seemingly esoteric whimsy of female choosiness for longer sperm may have surprisingly important consequences for biodiversity."

Judy Holmes | EurekAlert!
Further information:
http://www.syr.edu/

More articles from Life Sciences:

nachricht Rainbow colors reveal cell history: Uncovering β-cell heterogeneity
22.09.2017 | DFG-Forschungszentrum für Regenerative Therapien TU Dresden

nachricht The pyrenoid is a carbon-fixing liquid droplet
22.09.2017 | Max-Planck-Institut für Biochemie

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: The pyrenoid is a carbon-fixing liquid droplet

Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.

A warming planet

Im Focus: Highly precise wiring in the Cerebral Cortex

Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.

The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...

Im Focus: Tiny lasers from a gallery of whispers

New technique promises tunable laser devices

Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...

Im Focus: Ultrafast snapshots of relaxing electrons in solids

Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!

When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...

Im Focus: Quantum Sensors Decipher Magnetic Ordering in a New Semiconducting Material

For the first time, physicists have successfully imaged spiral magnetic ordering in a multiferroic material. These materials are considered highly promising candidates for future data storage media. The researchers were able to prove their findings using unique quantum sensors that were developed at Basel University and that can analyze electromagnetic fields on the nanometer scale. The results – obtained by scientists from the University of Basel’s Department of Physics, the Swiss Nanoscience Institute, the University of Montpellier and several laboratories from University Paris-Saclay – were recently published in the journal Nature.

Multiferroics are materials that simultaneously react to electric and magnetic fields. These two properties are rarely found together, and their combined...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

“Lasers in Composites Symposium” in Aachen – from Science to Application

19.09.2017 | Event News

I-ESA 2018 – Call for Papers

12.09.2017 | Event News

EMBO at Basel Life, a new conference on current and emerging life science research

06.09.2017 | Event News

 
Latest News

Rainbow colors reveal cell history: Uncovering β-cell heterogeneity

22.09.2017 | Life Sciences

Penn first in world to treat patient with new radiation technology

22.09.2017 | Medical Engineering

Calculating quietness

22.09.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>