The paper, “Extreme plasticity of reproductive state in a female rodent,” which published March 27 in Current Biology, explores how traits once considered “fixed” in adult animals may become variable under specific pressures.

Though these rodents could have important military, biodetection and humanitarian uses, breeding them at high rates has been a challenge. The study’s findings are a step toward understanding their reproductive biology, and possibly breeding them more effectively — and may even have broader implications for other mammals struggling to reproduce.

“The more we start to understand the full scope of the reproductive process, the more we can start to get insight into those sorts of questions,” said Alex Ophir, associate professor of psychology at Cornell University and the study’s senior author. “The more examples of other mammals we get, the better, and these unusual examples can sometimes reveal a lot about women’s health and reproductive health.”

While other species are known to undergo reproductive suppression — such as animals who only mate in certain seasons — most do this hormonally rather than closing off their genitals as giant African pouched rats do. More study is needed to understand why these rodents possess this unusual trait.

One hypothesis is that “dominant” female pouched rats might be sending suppression signals to other females through pheromones, or scents in their urine, that cause them to close up.

“You could interpret it as manipulation by one female to get other females to stop reproducing, and in effect, they’ll often in these cases, start to contribute to the care of the dominant reproducing female,” Ophir said.

Another theory could be tied to resource competition, where too many offspring in a population limits available food resources, and reducing the number of babies born to others could mean more resources for one’s own babies, Ophir said.

In future work, Ophir plans to continue investigating how the animals’ extraordinary olfactory systems work and hopes to learn more about their unusual behaviors and anatomies.

“The fact that there is this naturally occurring ability to sort of change reproductive morphology and physiology suggests that things are probably a whole lot more plastic than we realize,” Ophir said. “If nothing else, it just provides another example that things aren’t as dogmatically simple as people think.”

This study was funded by the Army Research Office.

Based in part on carbon emissions, a new study using simulations identified two tipping points for the Greenland Ice Sheet: releasing 1000 gigatons of carbon into the atmosphere will cause the southern portion of the ice sheet to melt; about 2500 gigatons of carbon means permanent loss of nearly the entire ice sheet.

Having emitted about 500 gigatons of carbon, we’re about halfway to the first tipping point.

“The first tipping point is not far from today’s climate conditions, so we’re in danger of crossing it,” said Dennis Höning, a climate scientist at the Potsdam Institute for Climate Impact Research who led the study. “Once we start sliding, we will fall off this cliff and cannot climb back up.”

The study was published in AGU’s journal Geophysical Research Letters, which publishes short-format, high-impact research spanning the Earth and space sciences.

The Greenland Ice Sheet is already melting; between 2003 and 2016, it lost about 255 gigatons (billions of tons) of ice each year. Much of the melt to date has been in the southern part of the ice sheet. Air and water temperature, ocean currents, precipitation and other factors all determine how quickly the ice sheet melts and where it loses ice.

The complexity of how those factors influence each other, along with the long timescales scientists need to consider for melting an ice sheet of this size, make it difficult to predict how the ice sheet will respond to different climate and carbon emissions scenarios.

Previous research identified global warming of between 1 degree to 3 degrees Celsius (1.8 to 5.4 degrees Fahrenheit) as the threshold beyond which the Greenland Ice Sheet will melt irreversibly.

To more comprehensively model how the ice sheet’s response to climate could evolve over time, Höning’s new study for the first time used a complex model of the whole Earth system, which includes all the key climate feedback processes, paired with a model of ice sheet behavior. They first used simulations with constant temperatures to find equilibrium states of the ice sheet, or points where ice loss equaled ice gain. Then they ran a set of 20,000-year-long simulations with carbon emissions ranging from 0 to 4000 gigatons of carbon.

From among those simulations, the researchers derived the 1000-gigaton carbon tipping point for the melting of the southern portion of the ice sheet and the even more perilous 2,500-gigaton carbon tipping point for the disappearance of nearly the entire ice sheet.

As the ice sheet melts, its surface will be at ever-lower elevations, exposed to warmer air temperatures. Warmer air temperatures accelerate melt, making it drop and warm further. Global air temperatures have to remain elevated for hundreds of years or even longer for this feedback loop to become effective; a quick blip of 2 degrees Celsius (3.6 degrees Fahrenheit) wouldn’t trigger it, Höning said. But once the ice crosses the threshold, it would inevitably continue to melt. Even if atmospheric carbon dioxide were reduced to pre-industrial levels, it wouldn’t be enough to allow the ice sheet to regrow substantially.

“We cannot continue carbon emissions at the same rate for much longer without risking crossing the tipping points,” Höning said. “Most of the ice sheet melting won’t occur in the next decade, but it won’t be too long before we will not be able to work against it anymore.”