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Will Climate Change Push These Amphibians to the Brink?

Animals
Will Climate Change Push These Amphibians to the Brink?
A California newt (Taricha torosa) from Napa County, California, USA. Connor Long / CC BY-SA 3.0

By Tara Lohan

Aerial photos of the Sierra Nevada — the long mountain range stretching down the spine of California — showed rust-colored swathes following the state's record-breaking five-year drought that ended in 2016. The 100 million dead trees were one of the most visible examples of the ecological toll the drought had wrought.

Now, a few years later, we're starting to learn about how smaller, less noticeable species were affected.


One of those is the California newt (Taricha torosa). These large, colorful amphibians live across the state, from Mendocino County to San Diego County, but newts living in Southern California fared worse during the drought, according to a new study published in the Nature journal Scientific Reports. And worse, anticipated future changes to the climate are likely to put northern newts in the same boat in coming decades.

Researchers have been surveying populations of these amphibians for decades. By tagging them with transponders and following their movements, they've learned that the newts can live for more than 30 years and return to the same spots year after year as they migrate between freshwater and land.

But as the drought began in 2012, the researchers noticed a change in the Southern Californian populations. There were fewer newts from the tagged population coming back to dozens of breeding sites monitored across the region each year. The researchers also observed fewer egg masses, tadpoles and larvae.

"Here's a long-lived species that we're not seeing individuals that we've seen for the last 10 or 15 years coming back to the sites where they usually breed," says Gary Bucciarelli, the lead author of the report and an assistant adjunct professor of ecology and evolutionary biology at UCLA.

And there was one more piece of bad news: Most of the adult newts that did return in Southern California were in poorer body condition than before the drought began. This negative trend, the researchers concluded, was linked to drier and warmer conditions that were far outside the 100-year average.

At the time the state was experiencing drought conditions not seen there for 1,200 years. You'd expect drought to hurt amphibians, which rely on access to water, but Bucciarelli says the research shows that similarly record-high air temperatures may have played an even greater role than precipitation.

Warmer temperatures remove necessary moisture from the terrestrial environment. But they could also affect food — a shifting climate may mean less prey, says Bucciarelli. Or it could mean that newts spend more time wandering around, burning calories, and less time hunkered down as they normally would.

Whatever exactly happened in this case, "It all was strongly correlated with the extreme deviation in climate," he adds.

Amphibians spend part of the year on land, and we know far less about how they spend their terrestrial days. "When they're on land we don't know if they're underground, moving around, in a deep sleep, or what they're feeding on," he says. "This research suggests there are things happening on land that are impacted by temperature that we don't really understand."

One thing is certain, though: Climate change will bring more severe droughts and higher temperatures to California, and that could push newts in Southern California, which are already a species of conservation concern, closer to extinction.

And in the next 50 years, the northern populations are likely to experience the same change in body condition. That means that the northern range "likely will not provide climate refuge for numerous amphibian communities," the researchers conclude.

That's particularly bad news considering that globally, an estimated 40% of amphibians face extinction. A disease caused by chytrid fungus has devastated many amphibian populations, especially in Australia, Central and South America, and wiped out 90 species already.

But amphibians face other threats, too. And the California newt is no exception.

The species is adapted to drought, but "they haven't dealt with drought coupled with temperature changes that are this rapid and this severe, in conjunction with habitat fragmentation, land use changes and fire frequency changes," Bucciarelli says. "Now we're beginning to see how these combined stressors are acting out ecologically."

So what do we do?

Collecting more data is a good start. Land managers need to begin long-term monitoring surveys of populations of amphibians now, even if the species aren't currently a major concern. "You never know what's going to happen and having baseline data is super important," he says.

Proactively improving habitat is also critical. We can start by ensuring that habitats are free of non-native species, says Bucciarelli, who has also tracked the negative effects of introduced fish and invasive crayfish on amphibians.

Suitable habitat is key, but so is connection. Many newt populations in Southern California have become islands, separated by development that limits their genetic diversity — and in the long run, their capacity to adapt to rapidly changing environmental conditions. Ensuring habitat connectivity could help strengthen their resilience.

Even if all of that happens, climate change will continue to be a threat, and Bucciarelli says we may need to develop contingency plans for worsening conditions if we hope to save these newts.

"We'll have to think of different and more creative management strategies to help in years when temperature and precipitation are not in line with the norm."

Tara Lohan is deputy editor of The Revelator.

Reposted with permission from our media associate The Revelator.

A net-casting ogre-faced spider. CBG Photography Group, Centre for Biodiversity Genomics / CC BY-SA 3.0

Just in time for Halloween, scientists at Cornell University have published some frightening research, especially if you're an insect!

The ghoulishly named ogre-faced spider can "hear" with its legs and use that ability to catch insects flying behind it, the study published in Current Biology Thursday concluded.

"Spiders are sensitive to airborne sound," Cornell professor emeritus Dr. Charles Walcott, who was not involved with the study, told the Cornell Chronicle. "That's the big message really."

The net-casting, ogre-faced spider (Deinopis spinosa) has a unique hunting strategy, as study coauthor Cornell University postdoctoral researcher Jay Stafstrom explained in a video.

They hunt only at night using a special kind of web: an A-shaped frame made from non-sticky silk that supports a fuzzy rectangle that they hold with their front forelegs and use to trap prey.

They do this in two ways. In a maneuver called a "forward strike," they pounce down on prey moving beneath them on the ground. This is enabled by their large eyes — the biggest of any spider. These eyes give them 2,000 times the night vision that we have, Science explained.

But the spiders can also perform a move called the "backward strike," Stafstrom explained, in which they reach their legs behind them and catch insects flying through the air.

"So here comes a flying bug and somehow the spider gets information on the sound direction and its distance. The spiders time the 200-millisecond leap if the fly is within its capture zone – much like an over-the-shoulder catch. The spider gets its prey. They're accurate," coauthor Ronald Hoy, the D & D Joslovitz Merksamer Professor in the Department of Neurobiology and Behavior in the College of Arts and Sciences, told the Cornell Chronicle.

What the researchers wanted to understand was how the spiders could tell what was moving behind them when they have no ears.

It isn't a question of peripheral vision. In a 2016 study, the same team blindfolded the spiders and sent them out to hunt, Science explained. This prevented the spiders from making their forward strikes, but they were still able to catch prey using the backwards strike. The researchers thought the spiders were "hearing" their prey with the sensors on the tips of their legs. All spiders have these sensors, but scientists had previously thought they were only able to detect vibrations through surfaces, not sounds in the air.

To test how well the ogre-faced spiders could actually hear, the researchers conducted a two-part experiment.

First, they inserted electrodes into removed spider legs and into the brains of intact spiders. They put the spiders and the legs into a vibration-proof booth and played sounds from two meters (approximately 6.5 feet) away. The spiders and the legs responded to sounds from 100 hertz to 10,000 hertz.

Next, they played the five sounds that had triggered the biggest response to 25 spiders in the wild and 51 spiders in the lab. More than half the spiders did the "backward strike" move when they heard sounds that have a lower frequency similar to insect wing beats. When the higher frequency sounds were played, the spiders did not move. This suggests the higher frequencies may mimic the sounds of predators like birds.

University of Cincinnati spider behavioral ecologist George Uetz told Science that the results were a "surprise" that indicated science has much to learn about spiders as a whole. Because all spiders have these receptors on their legs, it is possible that all spiders can hear. This theory was first put forward by Walcott 60 years ago, but was dismissed at the time, according to the Cornell Chronicle. But studies of other spiders have turned up further evidence since. A 2016 study found that a kind of jumping spider can pick up sonic vibrations in the air.

"We don't know diddly about spiders," Uetz told Science. "They are much more complex than people ever thought they were."

Learning more provides scientists with an opportunity to study their sensory abilities in order to improve technology like bio-sensors, directional microphones and visual processing algorithms, Stafstrom told CNN.

Hoy agreed.

"The point is any understudied, underappreciated group has fascinating lives, even a yucky spider, and we can learn something from it," he told CNN.

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