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Fish Markets: Cooperation and Competition in the Undersea "Economy"

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You probably know that hermit crabs live in shells. What you might not know is that really nice shells to call home are a scarce commodity, and hermit crabs consequently have some pretty cool ways of optimizing the ways they acquire and occupy their shells.

A study of the purple-clawed hermit crabs (Coenobita clypeatus) on an island off the Belizean coast reveals that the crabs fill shells using "vacancy chains"—social structures through which vacancies in certain resources propagate through a population, like the ways humans fill jobs and apartments.

Synchronous and Asynchronous Vacancy Chains

The hermit crabs were observed to use two types of vacancy chain: synchronous and asynchronous. An asynchronous chain is when one crab moves into a new, empty shell and abandons its old one to be found by another crab, which abandons its own for another crab to find, etc. With this type of chain, shell switching is sequential and the crabs experience little to no interference or competition. They have the opportunity to investigate any vacant shells they find and can directly compare their current shell with a new shell by switching back and forth between the two. It's sort of like when you look at apartments that have just been moved out of and are available immediately or in the near future. If you take one of those apartments, someone else can check out and move into yours, someone else will move into theirs, etc., in an orderly fashion.

Synchronous vacancy chains are more social and much more interesting. They start off with "waiters," crabs that hang around a shell that's too big for them, and wait for a bigger crab to come along so that if the big crab moves in to the vacant shell, the waiter can grab their more appropriately-sized hand-me-down shell. (The researchers note that the decision to wait, and how long to wait, based on previous experience, provides some evidence that the crabs are smarter than we thought.)

As a crowd gathers—a crowd always gathers, but no one knows how; the researchers think the waiters may use vocal or chemical signals to draw attention to the vacancy—the crabs queue up by size, from largest to smallest. Once the largest crab switches into the vacant shell, each crab climbs into a new shell as it's vacated by the slightly larger crab ahead of it, quickly shuffling vacancies (literally) down the chain. A similar type of chain happens in college towns across America every fall. Students spend months "lining up" by finding apartments, packing and labeling boxes, and then—BAM!—a few thousand kids move in and out of apartments in one day.

Here's a synchronous chain in action.

The Undersea Service Industry

Moving away from real estate and into the service industry, animals still behave kind of like humans. They partner with other animals that provide the high-quality goods and services, cheat each other, and then threaten to take their business elsewhere in order to get what they want.

"Cleaner fish," which remove dead skin and parasites from other fish in a mutually beneficial relationship (they get a meal, and the other fish get groomed), have been known to make their "clients" wait for service and cheat them by feeding on healthy tissue or mucous instead of parasites. Clients don't have many options for ensuring good service. They can't demand their mucous back or complain to the Better Business Bureau. What they can do is go get cleaned somewhere else.

A study by a University of California, Santa Barbara biologist found that individuals of one type of cleaner fish near French Polynesia, the luestreak cleaner wrasse, have to compete for access to their preferred clients, the ornate butterfly fish. This competition gives clients with easy access to multiple "cleaner stations" - areas where the cleaner fish hang out and do their thing - the ability to get better service from cleaners, who apparently are cued to the fact that their customers can easily take their business elsewhere and are discouraged from cheating them.

This story originally appeared in a different format on Matt's website.

More Details Emerge About 'Oumuamua, Earth's First-Recorded Interstellar Visitor

In October, scientists using the University of Hawaii's Pan-STARRS 1 telescope sighted something extraordinary: Earth's first confirmed interstellar visitor. Originally called A/2017 U1, the once-mysterious object has a new name—'Oumuamua, according to Scientific American—and researchers continue to learn more about its physical properties. Now, a team from the University of Hawaii's Institute of Astronomy has published a detailed report of what they know so far in Nature.

Fittingly, "'Oumuamua" is Hawaiian for "a messenger from afar arriving first." 'Oumuamua's astronomical designation is 1I/2017 U1. The "I" in 1I/2017 stands for "interstellar." Until now, objects similar to 'Oumuamua were always given "C" and "A" names, which stand for either comet or asteroid. New observations have researchers concluding that 'Oumuamua is unusual for more than its far-flung origins.

It's a cigar-shaped object 10 times longer than it is wide, stretching to a half-mile long. It's also reddish in color, and is similar in some ways to some asteroids in our solar system, the BBC reports. But it's much faster, zipping through our system, and has a totally different orbit from any of those objects.

After initial indecision about whether the object was a comet or an asteroid, the researchers now believe it's an asteroid. Long ago, it might have hurtled from an unknown star system into our own.

'Oumuamua may provide astronomers with new insights into how stars and planets form. The 750,000 asteroids we know of are leftovers from the formation of our solar system, trapped by the Sun's gravity. But what if, billions of years ago, other objects escaped? 'Oumuamua shows us that it's possible; perhaps there are bits and pieces from the early years of our solar system currently visiting other stars.

The researchers say it's surprising that 'Oumuamua is an asteroid instead of a comet, given that in the Oort Cloud—an icy bubble of debris thought to surround our solar system—comets are predicted to outnumber asteroids 200 to 1 and perhaps even as high as 10,000 to 1. If our own solar system is any indication, it's more likely that a comet would take off before an asteroid would.

So where did 'Oumuamua come from? That's still unknown. It's possible it could've been bumped into our realm by a close encounter with a planet—either a smaller, nearby one, or a larger, farther one. If that's the case, the planet remains to be discovered. They believe it's more likely that 'Oumuamua was ejected from a young stellar system, location unknown. And yet, they write, "the possibility that 'Oumuamua has been orbiting the galaxy for billions of years cannot be ruled out."

As for where it's headed, The Atlantic's Marina Koren notes, "It will pass the orbit of Jupiter next May, then Neptune in 2022, and Pluto in 2024. By 2025, it will coast beyond the outer edge of the Kuiper Belt, a field of icy and rocky objects."

Last month, University of Wisconsin–Madison astronomer Ralf Kotulla and scientists from UCLA and the National Optical Astronomy Observatory (NOAO) used the WIYN Telescope on Kitt Peak, Arizona, to take some of the first pictures of 'Oumuamua. You can check them out below.

Images of an interloper from beyond the solar system — an asteroid or a comet — were captured on Oct. 27 by the 3.5-meter WIYN Telescope on Kitt Peak, Ariz.
Images of 'Oumuamua—an asteroid or a comet—were captured on October 27.

U1 spotted whizzing through the Solar System in images taken with the WIYN telescope. The faint streaks are background stars. The green circles highlight the position of U1 in each image. In these images U1 is about 10 million times fainter than the faint
The green circles highlight the position of U1 in each image against faint streaks of background stars. In these images, U1 is about 10 million times fainter than the faintest visible stars.
R. Kotulla (University of Wisconsin) & WIYN/NOAO/AURA/NSF

Color image of U1, compiled from observations taken through filters centered at 4750A, 6250A, and 7500A.
Color image of U1.
R. Kotulla (University of Wisconsin) & WIYN/NOAO/AURA/NSF

Editor's note: This story has been updated.

Scientists Analyze the Moods of 90,000 Songs Based on Music and Lyrics

Based on the first few seconds of a song, the part before the vocalist starts singing, you can judge whether the lyrics are more likely to detail a night of partying or a devastating breakup. The fact that musical structures can evoke certain emotions just as strongly as words can isn't a secret. But scientists now have a better idea of which language gets paired with which chords, according to their paper published in Royal Society Open Science.

For their study, researchers from Indiana University downloaded 90,000 songs from Ultimate Guitar, a site that allows users to upload the lyrics and chords from popular songs for musicians to reference. Next, they pulled data from labMT, which crowd-sources the emotional valence (positive and negative connotations) of words. They referred to the music recognition site Gracenote to determine where and when each song was produced.

Their new method for analyzing the relationship between music and lyrics confirmed long-held knowledge: that minor chords are associated with sad feelings and major chords with happy ones. Words with a negative valence, like "pain," "die," and "lost," are all more likely to fall on the minor side of the spectrum.

But outside of major chords, the researchers found that high-valence words tend to show up in a surprising place: seventh chords. These chords contain four notes at a time and can be played in both the major and minor keys. The lyrics associated with these chords are positive all around, but their mood varies slightly depending on the type of seventh. Dominant seventh chords, for example, are often paired with terms of endearment, like "baby", or "sweet." With minor seventh chords, the words "life" and "god" are overrepresented.

Using their data, the researchers also looked at how lyric and chord valence differs between genres, regions, and eras. Sixties rock ranks highest in terms of positivity while punk and metal occupy the bottom slots. As for geography, Scandinavia (think Norwegian death metal) produces the dreariest music while songs from Asia (like K-Pop) are the happiest. So if you're looking for a song to boost your mood, we suggest digging up some Asian rock music from the 1960s, and make sure it's heavy on the seventh chords.


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