Learn about a bacterial electric grid; traits females have evolved to avoid harassment; and why tea leaves sink. There's a bacterial electric grid beneath our feet by Grant Currin Hidden bacterial hairs power nature’s “electric grid.” (2021, September). EurekAlert! https://www.eurekalert.org/news-releases/927031 Gu, Y., Srikanth, V., Salazar-Morales, A. I., Jain, R., O’Brien, J. P., Yi, S. M., Soni, R. K., Samatey, F. A., Yalcin, S. E., & Malvankar, N. S. (2021). Structure of Geobacter pili reveals secretory rather than nanowire behaviour. Nature, 597(7876), 430–434. https://doi.org/10.1038/s41586-021-03857-w Specktor, B. (2020, September 18). Scientists find “secret molecule” that allows bacteria to exhale electricity. Livescience.com; Live Science. https://www.livescience.com/electron-breathing-geobacter-microbes.html Basic Biology of Oral Microbes. (2015). Atlas of Oral Microbiology, 1–14. https://doi.org/10.1016/b978-0-12-802234-4.00001-x Many females have evolved traits to avoid harassment by Cameron Duke Berlin, S. (2021, August 30). Female Octopuses Throw Debris at Unwanted Mates Who Pester Them, Study Shows. Newsweek; Newsweek. https://www.newsweek.com/female-octopuses-throw-debris-unwanted-mates-who-pester-them-study-shows-1624345 Feldblum, Joseph T., Wroblewski, Emily E., Rudicell, Rebecca S., Hahn, Beatrice H., Paiva, T., Cetinkaya-Rundel, M., Pusey, Anne E., & Gilby, Ian C. (2014). Sexually Coercive Male Chimpanzees Sire More Offspring. Current Biology, 24(23), 2855–2860. https://doi.org/10.1016/j.cub.2014.10.039 Female hummingbirds avoid harassment by looking as flashy as males. (2021). Female hummingbirds avoid harassment by looking as flashy as males. Phys.org. https://phys.org/news/2021-08-female-hummingbirds-flashy-males.html Godfrey-Smith, P., Scheel, D., Chancellor, S., Linquist, S., & Lawrence, M. (2021). In the Line of Fire: Debris Throwing by Wild Octopuses. https://doi.org/10.1101/2021.08.18.456805 Hosken, D. J., Alonzo, S., & Wedell, N. (2016). Why aren’t signals of female quality more common? Exeter.ac.uk. https://doi.org/http://hdl.handle.net/10871/19606 Male-like ornamentation in female hummingbirds results from social harassment rather than sexual selection. (2021). Current Biology. https://doi.org/10.1016/j.cub.2021.07.043 Power Play. (2018). National Wildlife Federation. https://www.nwf.org/Magazines/National-Wildlife/2018/Oct-Nov/Animals/Animal-Aggression Wielgus, R. B., & Bunnell, F. L. (1994). Sexual Segregation and Female Grizzly Bear Avoidance of Males. The Journal of Wildlife Management, 58(3), 405. https://doi.org/10.2307/3809310 Why do tea leaves sink? by Ashley Hamer originally aired June 10, 2018 https://omny.fm/shows/curiosity-daily/the-cutest-kind-of-puppy-rural-happiness-and-the-s James Norwood Pratt. (2010, August 16). The Ancient and Best Way to Brew Loose-Leaf Tea. The Atlantic. https://www.theatlantic.com/health/archive/2010/08/the-ancient-and-best-way-to-brew-loose-leaf-tea/61479/ Inglis-Arkell, E. (2014, May 6). Why Do Your Tea Leaves Move To The Middle Of The Cup? Gizmodo. https://gizmodo.com/why-do-your-tea-leaves-move-to-the-middle-of-the-cup-1572125743 Ouellette, J. (2016). The Strange Physics of Tea Leaves Floating Upstream. Nautilus. https://nautil.us/blog/the-strange-physics-of-tea-leaves-floating-upstream Follow Curiosity Daily on your favorite podcast app to learn something new every day withCody Gough andAshley Hamer. Still curious? Get exclusive science shows, nature documentaries, and more real-life entertainment on discovery+! Go to https://discoveryplus.com/curiosity to start your 7-day free trial. discovery+ is currently only available for US subscribers.
Learn about a bacterial electric grid; traits females have evolved to avoid harassment; and why tea leaves sink.
There's a bacterial electric grid beneath our feet by Grant Currin
Many females have evolved traits to avoid harassment by Cameron Duke
Why do tea leaves sink? by Ashley Hamer originally aired June 10, 2018 https://omny.fm/shows/curiosity-daily/the-cutest-kind-of-puppy-rural-happiness-and-the-s
Follow Curiosity Daily on your favorite podcast app to learn something new every day with Cody Gough and Ashley Hamer. Still curious? Get exclusive science shows, nature documentaries, and more real-life entertainment on discovery+! Go to https://discoveryplus.com/curiosity to start your 7-day free trial. discovery+ is currently only available for US subscribers.
Find episode transcript here: https://curiosity-daily-4e53644e.simplecast.com/episodes/bacterial-electric-grid-females-fight-back-why-tea-leaves-sink
CODY: Hi! You’re about to get smarter in just a few minutes with Curiosity Daily from curiosity-dot-com. I’m Cody Gough.
ASHLEY: And I’m Ashley Hamer. Today, you’ll learn about a bacterial electric grid beneath our feet; traits that many female animals have evolved to avoid harassment; and why tea leaves sink.
CODY: Let’s satisfy some curiosity.
There's a bacterial electric grid beneath our feet by Grant Currin (Ashley)
There’s a natural electric grid beneath your feet. It’s formed by nanowires produced by billions of electricity-producing bacteria. And researchers have recently made a new discovery that could help us harness this natural power for our own uses.
But let’s back up: why would bacteria make electricity in the first place? Well, everything that’s alive has to turn nutrients into energy. It turns out that the process of turning nutrients into useful
energy creates a byproduct: extra electrons. Most organisms get rid of their extra electrons by transferring them to oxygen molecules in their cells.
But not every organism has access to oxygen, including bacteria that live in soil deep underground. So they’ve evolved an unusual solution. They “exhale” their extra electrons into underground minerals, like iron oxide. But as any electrician knows, electricity won’t travel through just anything. You need wires. And these electrogenic bacteria make their own. Researchers call them nanowires, and they’re trying to figure out how to put them to good use.
For a long time, scientists thought the nanowires were made out of a protein they already knew about, called pili. Lots of bacteria have pili — if you’ve ever seen a cartoon drawing of a bacterium, you’ve seen them; they’re the little hairs that stick out of the membrane. Most bacteria use these hairs to move around and to interact with other bacteria, so it only made sense that these bacteria would use them to transfer electricity. But it turns out that’s not what happens.
The researchers behind the new discovery started by growing some of their own microbes in the lab. Then they used a technique called cryogenic electron microscopy to take a very, very close look at the nanowires. What they found was quite a surprise. Pili aren’t nanowires at all. Instead, the pili of these bacteria are tiny little machines located on their insides. They work like pistons to pump out chains of different proteins that do form nanowires. And those nanowires pump out electrons. Together, those nanowires make a huge, electrified web.
This new discovery changes a lot of what scientists thought they knew. The researchers say scientists have published thousands of studies that were based on the old idea about pili and nanowires. And of course, it could have practical applications. These findings might help researchers design bacteria that generate useful energy for us oxygen-breathing humans to use. It’s further proof that one species’s trash is another species’s treasure.
Many females have evolved traits to avoid harassment by Cameron Duke (Cody)
Nobody likes being catcalled, and that includes wildlife. The truth for many animals is that males are aggressive, sometimes especially toward females. That’s why females of many species have literally evolved traits to avoid harassment. Some are pretty ingenious — and occasionally even help them fight back.
Some animals do this through camouflage. One recent study found that some female hummingbirds disguise themselves as brightly colored males to avoid their aggressive strikes while feeding. In the same way, female African swallowtail butterflies dodge aggressive males just by looking like them. Yes, you heard me right: aggressive male butterflies.
But other females take more aggressive tactics. Female octopuses being harassed by males were seen picking up rocks and debris to throw at their harassers. There’s power in groups, too. Females of many mammal species will often band together and synchronize their births to protect each other. Everybody needs a good wingwoman!
Females of more solitary species, like bears and whales, will avoid males almost completely — they’ll just mate and leave. This is what biologists call the male avoidance hypothesis, and it might explain why so many species are raised by their mothers alone. Some biologists think that male aggression might also explain why many species with colorful males have drab females. Any females that actively signal their quality as mates would be the target of extra harassment.
Male aggression toward females is kind of a dark side to sexual selection. Typically, sexual selection is associated with fun male traits, like big, beautiful peacock tails and TikTok-worthy mating dances. But sometimes this type of evolution leads to aggressive and intimidating behaviors geared toward the females they’re trying to mate with. A 2014 study found that sexual aggression in chimpanzees results in more offspring, which helps to spread these aggressive male traits. And like we’ve already covered, it’s not just chimps. Sexual aggression is common in species ranging from butterflies to whales and many things in between.
It turns out that sexual selection isn’t just about a male’s audition for a role — it’s an arms race between pushy males and picky females. And when the males get aggressive, females can fight back.
[A] Why do tea leaves sink? [2:00] by Ashley Hamer (Ashley)
ASHLEY: You know, over the years, we’ve gotten a lot of great questions from awesome listeners like you. And some of those questions even pop up more than once — including this classic question from 2018. A listener named Victoria wanted to know why tea leaves sink. She wrote, quote: “When hot water is poured on a tea leaf, doesn’t it heat up and expand? So there should be more surface area, making it float! Plus it’s diffusing out flavor and aroma into the tea, so shouldn’t it be even lighter than before? BUT IT MAGICALLY SINKS!! WHY?” Here’s what we discovered.
[ASHLEY: Clip 2:00]
RECAP
Let’s recap the main things we learned today
1. CODY: There’s a huge electricity grid in the soil beneath your feet. It’s formed by bacteria that “exhale” electrons into nearby soil minerals, and they do it using nanowires. Scientists recently realized they were totally wrong about what those nanowires were
made of, and now that they’ve fixed their mistake, it could lead to new developments in clean energy.
a. This isn’t the first story we’ve run on electrogenic bacteria: last October, we talked about how you have electrogenic bacteria in your gut. Like, you’ve probably heard of lactobacillus, the so-called “good” bacteria in yogurt? It’s electrogenic. Wild, right? You can find a link to that episode in the show notes.
2. ASHLEY: When male animals get aggressive, females have ways of fighting back. Some do it through camouflage, like how some female hummingbirds have flashy colors just like the males do. Some do it by fighting back, like the way female octopuses were seen throwing rocks at their harassers. And some do it by avoiding males entirely, like solitary bears and whales do.
3. CODY: Tea leaves sink because they get waterlogged. Dry tea leaves are lighter than water, which is why they float at first. But eventually, water fills the spaces in all the leaves. Another tea physics phenomenon was the “tea leaf paradox,” which is about how when you stir a teacup, water rushes to the outside but tea leaves collect in the middle. That paradox was explained by Albert Einstein himself, who found that the fast-moving water on the outer edge of the mug creates a zone of high pressure, and tea leaves tend to collect where there’s less pressure. Weird stuff.
a. Marangoni effect: This is all about how when you have a zone of high surface tension and a zone of low surface tension, the liquid will want to pull away from the low surface tension toward the high. Hotter liquids have higher surface tension, so the hot water in the kettle has higher surface tension than the less-hot water in the tea cup, and that leads some of the liquid to travel up the water spout, taking some tea leaves with it.
[ad lib optional]
ASHLEY: Today’s writers were Grant Currin and Cameron Duke.
CODY: Our managing editor is Ashley Hamer, who was also a writer on today’s episode. ASHLEY: Our producer and audio editor is Cody Gough.
CODY: [AD LIB SOMETHING FUNNY] Join us again tomorrow to learn something new in just a few minutes.
ASHLEY: And until then, stay curious!