New sperm-catching beads could someday help prevent pregnancy — or enable it.

Researchers created microscopic polymer beads that mimic unfertilized eggs and trap passing sperm. The beads are coated in the sperm-binding section of a protein called ZP2. In mammals, ZP2 is found in membranes around unfertilized eggs; sperm must bind to the protein before entering the egg.

The beads could be used as short-term contraceptives, Jurrien Dean of the National Institutes of Health in Bethesda, Md., and colleagues report in the April 27 Science Translational Medicine. In the laboratory, human sperm attached to the beads within five minutes. The researchers then mixed 100,000 human sperm with 1.5 million beads and 28 mouse eggs containing human ZP2 proteins. After 16 hours, only one sperm reached an egg.
In another experiment, beads coated with mouse ZP2 delayed pregnancy when injected into the uteruses of mating female mice. Bead-free mice took just over 28 days, on average, to conceive and give birth; bead-treated mice didn’t have babies for nearly 73 days on average. The beads didn’t appear to cause swelling or damage, and treated mice were able to give birth again within five months.

The beads could also help combat infertility. In an egg-penetration test, researchers gently detached bead-captured sperm and pitted those sperm against a control batch of sperm that had not been exposed to the beads. More than half of eggs (mouse eggs with human ZP2) exposed to the bead-selected sperm ended up with three or more sperm attached to them; none of the eggs exposed to the control group snagged three or more sperm. In fact, the control group failed to penetrate 38 out of 50 eggs. So the beads could someday be used to select healthy sperm for assisted reproduction, the researchers say.

But it’s not clear if the ability to bind to ZP2 necessarily indicates a healthy sperm, says Andrew La Barbera, chief scientific officer of the American Society for Reproductive Medicine in Birmingham, Ala. “Sperm selection is a very complex undertaking because of the fact that sperm are very complex,” he says. “We don’t know what makes a good sperm.”

Contraception might be a more reasonable future use for the beads, although allowing fertilization of one in 28 eggs is underwhelming, La Barbera says. Birth control should be closer to 99.9 percent effective. “It only takes one sperm to fertilize an egg,” he says. Still, the beads’ performance at blocking pregnancy in mice seems promising, La Barbera says. Future experiments would need to determine if the beads are safe and effective in women, and how many beads are needed to prevent conception.

Dean notes that the study is a proof of principle. Many unknowns must be evaluated before using the beads for birth control, including the side effects of long-term use, he says. “Although promising, we are a long way from translating these basic laboratory observations into useful clinical applications that provide people with better reproductive choices.”

During the rainy season in the Orinoco Llanos of Columbia and Venezuela, an odd landscape feature appears in places: mounds of grassy plants, as big as five meters across and two meters tall, surrounded by water. Traversing this landscape, called surales, requires either hopping from mound to mound or trudging through the boggy bits in between.

Locals and scientists have generally agreed that some kind of earthworm creates the mounds, but what species and how it does so has been a mystery. Now Anne Zangerlé of the Braunschweig University of Technology in Germany and colleagues report that they’ve found the culprit — giant Andiorrhinus earthworms, which can grow to a meter in length as juveniles. And the mounds themselves, the team reports May 11 in PLOS ONE, are actually made mostly of earthworm poop.

Zangerlé and her colleagues used Google Earth images to locate surales landscapes, finding that they come in the shape of both mounds and labyrinths. Leaving the complex labyrinths for a future study, the team studied the mounds and the lands on which they were found in both the rainy and dry seasons. They characterized the soil and the plants and worms living in and on the mounds. And then they pieced all of that information together to come up with a scenario that they think explains the construction of the mounds.
Andiorrhinus earthworms deposit feces, or casts, in towers that give the worms access to the air so they can breathe. The worms then return to the tower, depositing more and more material, building the tower into a mound. These young mounds, the researchers found, are dominated by Andiorrhinus earthworms. But over time, as the mounds get even bigger, other worm species begin to make their home there, as well as plants and, eventually, if the mounds get big enough, trees.

The Andiorrhinus earthworms tend to stay around the same mound because, as they build, they excavate soil from the region around the mound. That moat gets deeper and deeper until it becomes a barrier to the giant earthworm that created it.

The researchers don’t quite understand everything that is happening in the system. For example, there could be an as-yet-unknown end stage to mound development, or some kind of equilibrium state for the landscape. But they note that “these ecosystems are under threat from industrial agriculture, and are being leveled to make way for highly intensified commercial production of rice.” Because of that, they say, there is a risk that these wonderfully complex and mysterious systems could disappear before anyone fully understands what made them in the first place.

Earth’s plate tectonics could be a passing phase. After simulating rock and heat flow throughout a planet’s lifetime, researchers have proposed that plate tectonics is just one stage of a planet’s life cycle.

In the simulation, the Earth’s interior was too hot and runny at first to push around the giant chunks of crust, researchers report in the June Physics of the Earth and Planetary Interiors. After the interior cooled for around 400 million years, tectonic plates began shifting and sinking, though the process was stop-and-go for about 2 billion years. The simulation suggests that Earth now is nearly halfway through its tectonic life cycle, says study coauthor Craig O’Neill, a planetary scientist at Macquarie University in Sydney. In around 5 billion years, plate tectonics will grind to a halt as the planet chills.

The long delay before full-blown plate tectonics hints that the process could one day begin on currently stagnant planets, says Julian Lowman, a geodynamicist at the University of Toronto who was not involved in the research. “There is a possibility that plate tectonics could start up on Venus if conditions were right,” he says.
Plate tectonics regulates a planet’s climate by adding and removing carbon dioxide from the atmosphere. This climate control helps maintain Earth’s habitability. Plate movement is driven by heat flow through the planet’s interior. Simulating that heat flow requires complex calculations. Previous simulations were simplified and typically considered only snapshots of Earth’s history and missed how plate tectonics evolves over time.

O’Neill and colleagues simulated Earth’s full tectonic life span, starting with the planet’s formation around 4.5 billion years ago and looking ahead to around 10 billion years in the future. Even using a supercomputer and simulating only a two-dimensional cross section of the planet, the calculations took weeks.

The new timeline suggests that Earth’s plate tectonics is just a midpoint in the planet’s evolution between two stagnant states. Planets with different starting temperatures than Earth’s follow different trajectories, the team found. Colder planets may exhibit plate tectonics throughout their history while hotter planets could go for billions of years without plate tectonics.

Just because a planet currently lacks plate tectonics doesn’t make it uninhabitable, O’Neill says. Life potentially appeared on Earth as early as around 4.1 billion years ago (SN Online: 10/19/2015), a time when the new simulation suggests that Earth lacked full-blown plate tectonics. “Stagnant planets, depending on when they are in their history, can be equally likely of supporting habitable conditions” as planets with plate tectonics, O’Neill says.