That "Fresh Cut Grass" Smell Is a Distress Signal

inga/iStock via Getty Images
inga/iStock via Getty Images

Trauma, that’s what. It’s the smell of chemical defenses and first aid. The fresh, “green” scent of a just-mowed lawn is the lawn trying to save itself from the injury you just inflicted.

Leafy plants release a number of volatile organic compounds called green leaf volatiles (GLVs). When the plants are injured, whether through animals grazing on them, you cutting or mowing them, or even just unintentionally rough handling, these emissions increase like crazy.

The rush of chemicals does a few things. Some of the compounds stimulate the formation of new cells at the wound site so it closes faster. Others act as antibiotics that prevent bacterial infection and inhibit fungal growth. A few spur the production of defensive compounds at un-wounded sites as sort of a pre-emptive fortification. And still others react with other chemicals to act as something like distress signals. Scientists found in one study that the saliva of certain caterpillars reacts with the GLVs released by coyote tobacco plants to make them attractive to the "big-eyed bugs" that regularly eat the caterpillars.

Thankfully, the mix of lawnmower blades and GLVs won't get you eaten. Instead, humans get a treat. Among the GLVs released by damaged grass are a group of eight related oxygenated hydrocarbons, including aldehydes and alcohols, that cause the “green odor.”

There may be a high cost to that wonderful smell, though. These compounds are precursors to ozone formation, according to Australian researchers, and can contribute to the formation of photochemical smog in urban areas.

Science Finds a Better Way to Calculate 'Dog Years'

thegoodphoto/iStock via Getty Images
thegoodphoto/iStock via Getty Images

Anyone who has ever owned a pet is likely familiar with the concept of “dog years,” which suggests that one year for a dog is like seven years for a human. Using this conversion metric, a 2-year-old dog is akin to a high school freshman, while a 10-year-old dog is ready for an assisted living facility.

If that seems rather arbitrary, that’s because it is. But now, researchers at the University of California, San Diego have come to a more data-based measurement on dog aging through DNA.

The paper, published on the preprint server bioRxiv, based the finding on DNA methylation, a process in which molecules called methyl groups attach themselves to DNA and serve as an indicator of aging. Generally speaking, the older living beings get, the faster the rate of methylation. In the study, 104 Labrador retrievers were examined, with subjects ranging from 1 month to 16 years old. The results of their DNA methylation were compared to human profiles. While the rate of methylation tracked closely between the two—young and old dogs had similar rates to young and old people—adolescent and mature dogs experienced more accelerated aging.

Their recommended formula for comparing dog and human aging? Multiply the natural logarithm of a dog’s age by 16, then add 31. Or, just use this calculator. Users will see that a 2-year-old dog, for example, wouldn’t be the canine equivalent of a 14-year-old. It would be equivalent to 42 human years old and should probably start putting money into a 401(k). But because methylation slows considerably in mid-life, a 5-year-old dog is approximately a 57-year-old human, while a 6-year-old dog is nearing 60 in human years—a minor difference. Things level out as the dog gets much older, with a 10-year-old dog nearing a 70-year-old human.

Different breeds age at different rates, so the formula might not necessarily apply to other dog breeds—only Labs were studied. The work is awaiting peer review, but it does offer a promising glimpse into how our furry companions grow older.

[h/t Live Science]

Sssspectacular: Tree Snakes in Australia Can Actually Jump

sirichai_raksue/iStock via Getty Images
sirichai_raksue/iStock via Getty Images

Ophidiophobia, or fear of snakes, is common among humans. We avoid snakes in the wild, have nightmares about snakes at night, and recoil at snakes on television. We might even be born with the aversion. When researchers showed babies photos of snakes and spiders, their tiny pupils dilated, indicating an arousal response to these ancestral threats.

If you really want to scare a baby, show them footage of an Australian tree snake. Thanks to researchers at Virginia Tech, we now know these non-venomous snakes of the genus Dendrelaphis can become airborne, propelling themselves around treetops like sentient Silly String.

That’s Dendrelaphis pictus, which was caught zipping through the air in 2010. After looking at footage previously filmed by her advisor Jake Socha, Virginia Tech Ph.D. candidate Michelle Graham headed for Australia and built a kind of American Ninja Warrior course for snakes out of PVC piping and tree branches. Graham observed that the snakes tend to spot their landing target, then spring upward. The momentum gets them across gaps that would otherwise not be practical to cross.

Graham next plans to investigate why snakes feel compelled to jump. They might feel a need to escape, or continue moving, or do it because they can. Two scientific papers due in 2020 could provide answers.

Dendrelaphis isn’t the only kind of snake with propulsive capabilities. The Chrysopelea genus includes five species found in Southeast Asia and China, among other places, that can glide through the air.

[h/t National Geographic]

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