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How Do Megamouth Sharks Glow?

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Despite being a massive shark (measuring up to 16 feet/5 meters in length), there is a lot shark scientists don’t know about megamouth sharks (Megachasma pelagios). With only 117 specimens observed and documented so far, this filter-feeding shark is one of the rarest big sharks known in the world!

The megamouth shark was first discovered in 1976 by a U.S. navy research vessel that was operating in Hawaiian waters. The shark had became tangled in some underwater cables and due to their mouths they were dubbed the ‘megamouth’ shark. Such a peculiar-looking animal, the deepwater shark is the sole member of its genus, Megachasma. Believed to be diurnal, it is thought to swim between the shallows and deep waters to follow swarms of zooplankton. “Unlike the other filter-feeding sharks, M. pelagios seems to possess a unique feeding method likely derived from the ram-filter mode used by the basking shark,” say the authors of a new study. “By creating a negative pressure when it expands maximally the oral cavity, it fills it and expulses the water through its gill slits when it closes it.”

As one can imagine, due to their rarity, very little is known about the shark’s behaviour or how their unique physical traits help them out. For example, it was believed their lips could possibly be bioluminescent, attracting prey into their mouth. Another hypothesis is that they use the unusual white band on their upper jaw to produce bioluminescence as a lure trap. This white band, hidden in a groove between their snout and the jaw, is only visible when their upper jaw is protruded. Could this somehow be linked to feeding?

Researchers led by scientists Laurent Duchatelet and Victoria C. Moris of Université Catholique de Louvain, Belgium wanted to find out what this band does for these mysterious sharks. After collecting tissue patches from specimens that were accidentally caught by local fishermen along the Japanese coast, the team used different techniques to find out more information about the samples collected (ratio of measures, shape, density, arrangement, surface features, calcification structure, and reflective properties).

Their analysis found that the band doesn’t emit its own bioluminescence but seems to reflect the light produced by bioluminescent planktonic preys, thanks to the denticles of the white band.

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science 

The ultraviolet glow around some galaxies may come from runaway stars

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Hot blue stars kicked out of their cradles may explain a mysterious ultraviolet glow that surrounds the disks of many spiral galaxies.

A new computer simulation demonstrates that these runaway stars can populate the vast expanses beyond a galaxy’s visible disk (SN: 3/23/20). These distant regions have gas that is too warm and tenuous to make new stars, yet young stars nevertheless exist there.

“It’s a big problem for classical star formation theory,” says Eric Andersson, an astrophysicist at Lund Observatory in Sweden.

The mystery of the far-flung young stars has persisted for some time. In 2003, NASA launched the Galaxy Evolution Explorer space telescope, which surprised astronomers by discovering diffuse far-ultraviolet light in the hinterlands of nearby spiral and irregular galaxies (SN: 2/15/05). Unlike ordinary ultraviolet radiation, far-ultraviolet light has such a short wavelength that most of it doesn’t penetrate the Earth’s atmosphere.

Stars that emit profuse amounts of this energetic radiation are hot, blue and usually much more massive than the sun. These stars don’t live long, so they must have formed recently. But the gas on the galactic outskirts isn’t cold and dense enough to collapse and create new stars.

Andersson and his colleagues propose a solution to the paradox: Many of these far-out far-ultraviolet-emitting stars weren’t born where they are now. Instead, they arose closer to the galaxy’s center and ran away from their homes.

The researchers conducted a computer simulation to model the motion of massive stars in a spiral galaxy. Some of the runaway stars in the simulation dart across thousands of light-years of space to take up residence beyond the visible edge of the galaxy’s disk, thereby explaining the far-ultraviolet light there, the researchers report online at arXiv.org on October 22.

The Milky Way has many of these runaway stars. A star can become a runaway when other massive stars fling it away through their gravity. Or, if the star orbits close to a massive star that explodes, the surviving star races away at the same speed it had been dashing around its companion. Most runaway stars are hot and blue, radiating just the type of far-ultraviolet light seen beyond the visible edges of galactic disks.

Mark Krumholz, an astronomer at the Australian National University in Canberra, calls the idea “a plausible explanation.” He also offers a way to test it: by exploiting the properties of different types of massive stars.

The rarest and most massive blue stars are so hot they ionize hydrogen gas, causing it to emit red light as electrons settle back into position around protons. But these very massive stars don’t live long, so any that reside on a galaxy’s outskirts must have been born there. After all, the stars didn’t have time to travel from elsewhere in the galaxy during their brief lives.

In contrast, less massive blue stars live longer and therefore

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science 

Platypuses Glow Under UV Light

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KEY POINTS

  • Researchers found that platypus fur actually glows under UV light
  • They made the discovery when studying the glow in another mammal species
  • The trait has been observed in many other animals but only a few mammals

What could possibly make the duck-billed platypus stranger that it already is? Researchers found that their fur also glows blue when placed under ultraviolet (UV) light.

Platypuses are some of the strangest creatures on the planet. They’re one of the very few mammals that lay eggs, they have bills and webbed feet similar to ducks’, their tails look rather like beaver tails and, apparently, they also glow an eerie shade of blue-green when exposed to UV light.

The latter was recently discovered by a team of scientists who were actually studying biofluorescence, the means by which creatures absorb and re-emit wavelengths of light, in the museum specimens of another species. According to a news release from De Gruyter, the team made the discovery while looking at flying squirrel museum specimens.

They had previously observed pink biofluorescence in flying squirrels and were confirming it in the museum specimens when they decided to also check the museum’s platypus samples for the trait.

There, they discovered that platypuses also possess biofluorescence, with their brown fur exhibiting a greenish glow under the UV light. The researchers tested another sample in different museum and also observed the glow.

“Here we document the discovery of fluorescence of the pelage of the platypus (Ornithorhynchus anatinus)—to our knowledge, the first report of biofluorescence in a monotreme mammal under UV light,” the researchers wrote in the study. 

In total, the researchers observed platypus biofluorescence in three museum samples, two of which were from the Field Museum of Natural History and the other from the University of Nebraska State Museum, the news release noted. 

“It was a mix of serendipity and curiosity that led us to shine a UV light on the platypuses at the Field Museum. But we were also interested in seeing how deep in the mammalian tree the trait of biofluorescent fur went,” study lead Paula Spaeth Anich of Northland College said in the news release. “It’s thought that monotremes branched off the marsupial-placental lineage more than 150 million years ago. So, it was intriguing to see that animals that were such distant relatives also had biofluorescent fur.”

But what could platypuses possibly have use for biofluorescence? It’s possible, the researchers say, that platypuses use this trait to interact with each other in the dark and to reduce their visibility to UV sensitive-predators.

It would be particularly useful since platypuses are most active at night and during low-light environments at dawn and dusk. However, field research is needed to confirm these hypotheses, the researchers said.

Biofluorescence has been observed in many other animals such as fishes, reptiles and amphibians, but only few mammalian species are known to posses biofluorescence, including the opossum and the flying squirrel. 

“The discovery of biofluorescence in the platypus adds a new dimension to our

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