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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.

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AMNH // R. Mickens
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science
What It’s Like to Write an Opera About Dinosaurs
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AMNH // R. Mickens

There are many challenges that face those writing the lyrics to operas, but figuring out what can rhyme with dinosaur names isn’t often one of them. But wrangling multisyllabic, Latin- and Greek-derived names of prehistoric creatures into verse was an integral part of Eric Einhorn’s job as the librettist behind Rhoda and the Fossil Hunt, a new, family-friendly opera currently running at the American Museum of Natural History in New York City.

Created by On Site Opera, which puts on operas in unusual places (like Madame Tussauds Wax Museum) across New York City, in conjunction with the Lyric Opera of Chicago and the Pittsburgh Opera, Rhoda and the Fossil Hunt follows the true story of Rhoda Knight and her grandfather, the famous paleoartist Charles R. Knight.

Knight worked as a freelance artist for the American Museum of Natural History from 1896 until his death in 1953, creating images of extinct species that paved the way for how we imagine dinosaurs even now. He studied with taxidermists and paleontology experts and was one of the first to paint dinosaurs as flesh-and-blood creatures in natural habitats rather than fantastical monsters, studying their bones and creating sculptural models to make his renderings as accurate as contemporary science made possible.

In the 20-minute opera, singers move around the museum’s Hall of Saurischian Dinosaurs, performing among skeletons and even some paintings by Knight himself. Einhorn, who also serves as the director of On Site Opera and stage director for the opera, wrote the libretto based on stories about the real-life Rhoda—who now goes by Rhoda Knight Kalt—whom he met with frequently during the development process.

Soprano Jennifer Zetland (Rhoda) sings in front of a dinosaur skeleton at the American Museum of Natural History.
AMNH // R. Mickens

“I spent a lot of time with Rhoda just talking about her childhood,” he tells Mental Floss, gathering anecdotes that could be worked into the opera. “She tells this great story of being in the museum when they were unpacking the wooly mammoth,” he says. "And she was just there, because her grandfather was there. It's being at the foot of greatness and not even realizing it until later.”

But there was one aspect of Rhoda’s childhood that proved to be a challenge in terms of turning her story into a performance. “Unfortunately, she was a really well-behaved kid,” Einhorn says. “And that doesn't really make for a good opera.”

Knight Kalt, who attended the opera’s dress rehearsal, explains that she knew at the time that if she misbehaved, she wouldn’t be allowed back. “I knew that the only way I could be with my grandfather was if I was very quiet,” she says. “Sometimes he would stand for an hour and a half discussing a fossil bone and how he could bring that alive … if I had interrupted then I couldn't meet him [at the museum anymore].”

Though Knight Kalt was never an artist herself, in the fictionalized version of her childhood (which takes place when Rhoda is 8), she looks around the museum for the missing bones of the dinosaur Deinocheirus so that her grandfather can draw them. The Late Cretaceous dino, first discovered in 1965, almost didn't make it into the show, though. In the first draft of the libretto, the dinosaur Rhoda is searching for in the museum was a relatively new dinosaur species found in China and first unveiled in 2015—zhenyuanlong suni—but the five-syllable name proved impossible to rhyme or sing.

Rhoda Knight Kalt stands next to the head of a dinosaur.
Rhoda Knight Kalt
Shaunacy Ferro

But Einhorn wanted to feature a real dinosaur discovery in the opera. A paleontologist at the museum, Carl Mehling, suggested Deinocheirus. “There are two arms hanging right over there,” Einhorn says, gesturing across the Hall of Saurischian Dinosaurs, “and until [recently] the arms were the only things that had ever been discovered about Deinocheirus.” Tying the opera back to an actual specimen in the museum—one only a few feet away from where the opera would be staged—opened up a whole new set of possibilities, both lyrically and otherwise. “Once we ironed that out, we knew we had good science and better rhyming words.”

As for Knight Kalt, she says the experience of watching her childhood unfold in operatic form was a little weird. “The whole story makes me laugh,” she says. But it was also a perfectly appropriate way to honor her grandfather. “He used to sing while he was painting,” she says. “He loved the opera.”

Performances of Rhoda and the Fossil Hunt will be performed at the American Museum of Natural History on Fridays, Saturdays, and Sundays until October 15. Performances are free with museum admission, but require a reservation. The opera will later travel to the Lyric Opera of Chicago and the Pittsburgh Opera.

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Animals
11 Buoyant Facts About Humpback Whales
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iStock

Humpback whales are some of the most intelligent animals on the planet. Hunted almost to extinction during the 19th and early 20th centuries, their populations are slowly recovering, and now they’re a favorite sight for whale-watchers. Here are 11 facts you might not have known about the mysterious marine giants, who are known for their acrobatics and for sidling right up alongside boats to get a good look at their human observers.

1. THEY’RE LONGER THAN A SCHOOL BUS.

North American school buses max out at about 45 feet long. Female humpback whales—which are larger than males—can be up to 60 feet long, and their pectoral fins alone can be 15 feet long. At birth, humpbacks weigh around 1 ton, doubling in size during their first year of life and eventually reaching up to 40 tons.

2. THEY HAVE HUGE MOUTHS.

In keeping with the rest of their bodies, their mouths are huge—their tongue alone is the size of a small car. But the opening to their throat is only about the size of a grapefruit, according to the Hawaiian Islands Humpback Whale National Marine Sanctuary, so they can’t swallow large prey. Instead, they eat krill, small fish, and plankton. They can eat up to a ton of food per day, according to the 2015 documentary Humpback Whales.

3. THOSE BUMPS ARE HAIR FOLLICLES.

Each of the distinctive bumps along a humpback’s head holds a single hair that the whale uses to sense the environment around it. These hairs help the whale glean information about water temperature and quality.

4. THEIR FLUKES ARE LIKE FINGERPRINTS.

Like human fingerprints, humpback tails can be used to identify individuals. The pigmentation and scarring on their flukes is unique, and scientists document these markings to keep track of certain whales that they see repeatedly during their research trips.

5. THEY LIVE A LONG TIME, BUT NOT AS LONG AS MANY OTHER WHALES.

Most humpback whales make it into their 60s, but scientists estimate that they may live up to 80 years. Still, that’s nothing compared to bowhead whales, a species whose oldest known individuals have lived to be 200 years old.

6. THEY HAVE THE LONGEST MIGRATIONS OF ANY MAMMAL.

Each year, humpbacks migrate from their feeding grounds in cold waters toward warm breeding areas—Alaskan whales head to Hawaii, while Californian whales head to Mexico and Costa Rica, and Australian whales migrate to the Southern Ocean. These biannual journeys can involve distances of up to 5000 miles, which is officially the longest known migration of any mammal on earth.

The fastest documented migration of a humpback whale was observed in 1988, when a humpback traveled from Sitka, Alaska to to Hawaii in just 39 days—or possibly less, depending on how soon it left Alaskan waters after the researchers sighted it the first time [PDF]. That’s a journey of about 2750 miles point to point.

7. THEY HAVE BEEN KNOWN TO DEFEND OTHER SPECIES FROM ORCAS.

In 2009, marine ecologist Robert Pitman watched two humpback whales rescue a seal from a group of orcas that were pursuing it. The seal ended up on one of the humpbacks’ chests, and when it began to fall off, the whale even nudged it back on with a flipper, indicating that it was an intentional act of altruism. Though it’s not entirely clear why they would do so, it appears to be an offensive response on the part of the humpbacks, who may intervene whenever they hear killer whales fighting, whether one of their own is involved or not.

8. ONLY THE MALES SING.

Their songs may have made the species famous, but not every humpback sings. It’s strictly a male behavior, and plays an important part in courtship displays. There’s plenty of mystery that still surrounds the science of whale songs, but in 2013, researchers discovered that it’s a group activity that involves even sexually immature males. Both young and mature whales sing in chorus, giving the immature whales a lesson in singing and courtship behavior, and helping older whales amplify their songs to draw females to the area from afar. Other research has found that these songs change over times, and whales learn them much like a human learns a new song, bit by bit.

9. BREACHING IS LIKE YELLING

Though humpbacks are famous for their songs, that’s not the only way they communicate. Scientists only recently discovered that breaching—when whales jump up into the air, crashing back down into the water—is a way to keep in touch with far-away friends. Humpbacks leap higher and more often than other whales, and while spectacular to witness, the moves come at a cost: It takes a lot of energy, especially when the whales are fasting. But after 200 hours observing humpbacks migrating past the Australian coast, a team from the University of Queensland found that the whales were more likely to breach when the nearest group of other humpbacks was more than two and a half miles away, and that they were more likely to do so when it was windy out. It appears that breaching is a way to communicate over long distances when there is a lot of competing noise.

10. THEIR SONGS ARE INCREDIBLY COMPLEX …

Humpback songs aren’t just showy. They have their own grammar, and their songs are hierarchical, like sentences. In human language, this means that the meaning of sentences depends on the clauses within them and the words within them. In 2006, mathematical analysis found that humpbacks use phrases, too. And they remix their tunes, too, tweaking them and changing them over time, often combining new and old melodies. Humpback songs have even been visualized as sheet music.

11. … AND HELPED END WHALING.

Researchers estimate [PDF] that prior to the whaling boom of the 19th and 20th centuries, there were around 112,000 humpbacks in the North Atlantic alone, but that by the time commercial whaling was banned in the region in 1955, there were less than 1000 individuals left. Between 1947 and the 1970s, the USSR alone killed an estimated 338,000 humpbacks, falsifying data it was required to submit to the International Convention for the Regulation of Whaling to disguise the illegal magnitude of its hunting operation. It has been called “one of the greatest environmental crimes of the 20th century.”

While the populations have grown and humpbacks have been taken off the endangered species list, some estimates put the worldwide humpback population at only 40 percent of what it was before the whaling era. Whaling was banned throughout the rest of the world in 1966, though Norway, Iceland, and Japan still practice it.

Roger Payne, one of the scientists who first discovered that humpbacks sing songs, later became instrumental in pushing to protect the species in the 1960s. In 1970, he released his recording of humpback songs as a record, which remains the best-selling nature recording in history. In 1972, the songs were played at a Greenpeace meeting, and ended up galvanizing a new movement: Save the Whales. “It certainly was a huge factor in convincing us that the whales were an intelligent species here on planet Earth and actually made music, made art, created an aesthetic,” as former Greenpeace director Rex Weyler told NPR in 2014. The campaign gained traction with other organizations, too, and helped lead to the International Whaling Commission’s 1982 whaling ban.

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