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Evolutionary Arms Race Between Plants and Caterpillars Created Mustard

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If you're a fan of mustard, wasabi or any other savory flavors that come from plants in the order Brassicales—cabbage, horseradish, kale or mustard—you have caterpillars' distaste for those exact flavors to thank for their existence. 

Some 90 million years ago, ancient Brassicales plants evolved to produce chemicals called glucosinolates as a defense against the cabbage butterfly caterpillars that were decimating the vegetation. This key component of mustard oil not only tasted bitter to the bugs, it was toxic for them—making it the perfect defense, at first. But over the course of the next 10 million years, the caterpillars, in turn, evolved a protein that allowed them to digest the chemical defense. This gave them a new food source all to themselves. The cabbage butterflies flourished and evolved into several new species, all with the ability to eat mustard oil plants.

Needing a new defense, the plants' evolution added in different amino acid ingredients to make new glucosinolates that allowed them to branch out into more species. And while that worked for a little while (you know, hundreds of thousands of years) you can probably guess what happened next.

This back and forth over the millennia was essentially an evolutionary arms race during which a pair of species pushed each other to keep up. The coevolution of cabbage butterflies and Brassicales plants has been known about for a while. But for a paper published this month in Proceedings of the National Academy of Sciences, a group of scientists led by J. Chris Pires, a plant evolutionary biologist at the University of Missouri, made a pair of evolutionary family trees. When they lined the two trees up, they noticed that the branching of the different species corresponded perfectly to the opposing group's new genetic feature. They were able to infer that they were not simply evolving alongside one another but in direct response to each other.

This worked out well for humans, who now enjoy a range of cruciferous vegetables that evolved from those ancient cabbage plants when the family tree expanded, and which get most of their flavor from the glucosinolates that originally developed to ward off caterpillars.

"Why do you think plants have spices or any flavor at all? It's not for us," Pires told NPR's The Salt. "They have a function. All these flavors are evolution."

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Scientists Accidentally Make Plastic-Eating Bacteria Even More Efficient
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In 2016, Japanese researchers discovered a type of bacteria that eats non-biodegradable plastic. The organism, named Ideonella sakaiensis, can break down a thumbnail-sized flake of polyethylene terephthalate (PET), the type of plastic used for beverage bottles, in just six weeks. Now, The Guardian reports that an international team of scientists has engineered a mutant version of the plastic-munching bacteria that's 20 percent more efficient.

Researchers from the U.S. Department of Energy's National Renewable Energy Laboratory and the University of Portsmouth in the UK didn't originally set out to produce a super-powered version of the bacteria. Rather, they just wanted a better understanding of how it evolved. PET started appearing in landfills only within the last 80 years, which means that I. sakaiensis must have evolved very recently.

The microbe uses an enzyme called PETase to break down the plastic it consumes. The structure of the enzyme is similar to the one used by some bacteria to digest cutin, a natural protective coating that grows on plants. As the scientists write in their study published in the journal Proceedings of the National Academy of Sciences, they hoped to get a clearer picture of how the new mechanism evolved by tweaking the enzyme in the lab.

What they got instead was a mutant enzyme that degrades plastic even faster than the naturally occurring one. The improvement isn't especially dramatic—the enzyme still takes a few days to start the digestion process—but it shows that I. sakaiensis holds even more potential than previously expected.

"What we've learned is that PETase is not yet fully optimized to degrade PET—and now that we've shown this, it's time to apply the tools of protein engineering and evolution to continue to improve it," study coauthor Gregg Beckham said in a press statement.

The planet's plastic problem is only growing worse. According to a study published in 2017, humans have produced a total of 9 billion tons of plastic in less than a century. Of that number, only 9 percent of it is recycled, 12 percent is incinerated, and 79 percent is sent to landfills. By 2050, scientists predict that we'll have created 13 billion tons of plastic waste.

When left alone, PET takes centuries to break down, but the plastic-eating microbes could be the key to ridding it from the environment in a quick and safe way. The researchers believe that PETase could be turned into super-fast enzymes that thrives in extreme temperatures where plastic softens and become easier to break down. They've already filed a patent for the first mutant version of the enzyme.

[h/t The Guardian]

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Ian Cartwright
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Stones, Bones, and Wrecks
An 88,000-Year-Old Middle Finger May Change What We Know About Human Migration
Ian Cartwright
Ian Cartwright

A middle finger might change what we thought we knew about human migration from Africa. As Gizmodo reports, a new study in Nature Ecology and Evolution analyzes what may be the oldest modern human fossil outside of Africa and the Levant (modern-day Israel, Lebanon, Syria, and Jordan). Found in an ancient lake bed in the Arabian desert, the bone has been dated to 88,000 years ago, indicating that human migration from Africa may have started much earlier than previously thought.

Previous research has suggested that Homo sapiens populations migrated out of Africa and into Eurasia (perhaps thanks to climate change) in one big wave around 60,000 years ago. The fossilized finger bone, about an inch long, indicates the story might be more complicated.

A paleontologist with the Saudi Geological Survey, Iyad Zalmout, found the bone in 2016. He and his fellow researchers created 3D scans of the bone and compared them with other finger bones from Homo sapiens, Neanderthals, and modern primates like gorillas to determine that it is, in fact, a human bone. They then dated the fossil using uranium series dating, a measure of the bone's ratio of radioactive elements, to arrive at an estimated age of roughly 88,000 years old. They also found animal fossils and sediment at the site to be around 90,000 years old.

A surveyor stands in the desert.
The area in Saudi Arabia where the finger was found.
Klint Janulis

At that time, the area in the Nefud Desert where the bone was found would have been semi-arid grasslands surrounding a freshwater lake, a more hospitable climate than it is today. At some parts during this era, the Red Sea between Africa and the Arabian Peninsula would have been low enough to make it essentially just a big river, so humans could have crossed there, as a related article in the journal by anthropologist Donald Henry notes.

Several scientists told Gizmodo that it's possible that the bone isn't human at all—it could belong to a relative of Homo sapiens—and that the authors of the new study are overstating the significance of their finding, so the analysis is somewhat controversial.

However, other evidence has pointed to an earlier African exit date for humans. In 2015, scientists in China discovered human teeth they dated to 80,000 years ago, though they weren't able to date the bone directly—instead, they analyzed the teeth's surroundings. In January 2018, scientists announced that they had found a partial jawbone in an Israeli cave dating back at least 177,000 years.

"The ability of these early people to widely colonize this region [of Arabia] casts doubt on long held views that early dispersals out of Africa were localized and unsuccessful," said lead author Huw Groucutt, of the University of Oxford and the Max Planck Institute for the Science of Human History, in a statement.

[h/t Gizmodo]

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