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Scyliorhinus canicula

Researchers identify previously unknown mechanism through which sharks produce eerie glow

Unlike other creature, glowing catsharks that are present in the saline depths have a fluorescence mechanism that could be conferring some serious perks – such as the ability to pick out other sharks among the many fluorescent things on the seafloor

Biologist David Gruber of the City University of New York said that after they first reported that swell sharks were bio fluorescent, he along with his collaborators decided to plunge deeper into the topic learning more about bio fluorescence and its meaning which is constantly evolving mystery. The study has been published in iScience.

Evolution is a funny thing. Animals that are very different from one another can end up doing the same cool tricks. This phenomenon is called parallel evolution, and it can be fascinating to observe.

Biofluorescence, as an example, is a phenomenon in which living organisms like frogs, scorpions, chameleons, turtles, and a whole plethora of sea creatures can absorb and re-emit light in a different colour which is not to be confused with bioluminescence in which organisms glow with the light they produce themselves.

Majority of animals fluoresce by producing a green fluorescent protein (GFP), proteins that are very similar to GFP, or fatty acid-binding proteins (FABP). But the biofluorescent glow produced by a different chemical pathway is seen only in the two species of catshark – The Chain Catshark (Scyliorhinus retifer) and the Swell Shark (Cephaloscyllium ventriosum) both of which are flecked with light and dark patterns.

The sharks’ glow is produced by brominated tryptophan-kynurenine small-molecule metabolites, found only in the lighter parts of patterned skin while it is involved in the immune system and the central nervous system in other vertebrates. The metabolites in the shark’s skin help produce fluorescence in low-light conditions on the seafloor.

This is invisible to the human eye but the sharks’ eyes can see it, that’s why fluorescence wasn’t discovered until 2014. They channel that fluorescence through their scales, or denticles specifically structured for the task, so that they gleam with the re-emitted green light.

Researchers think that as it’s a different chemical pathway from those used by other sea animals, it might be a secret visual language which only shark understand. Chemical biologist Jason Crawford of Yale University said that because of these biofluorescent characteristics that their skin shows and that their eyes can detect, they have a completely different view of the world and to see each other which no other animal can link to.

Researchers want to determine the role of metabolites in keeping the sharks clean. Both the species of catshark spend a lot of time in the sediment, which contains more bacteria than the water column and having anti-fouling properties. Staphylococcus aureus and Vibrio parahaemolyticus, the two bacterial pathogens when pitted against isolated metabolites, two of the metabolites showed some ability to inhibit the growth of these bacteria showing antimicrobial properties.

Gruber said that sharks have been fascinating creatures for over 400 million years and the study highlights yet another mystery of sharks and inspires us to learn more about their secrets and work to better protect them.

Journal Reference: iScience

pumpkin toadlets

Scientists discover fluorescence in frogs of Atlantic Forest

In the Atlantic Forest in Eastern Brazil, the pumpkin toadlets use their bright colours to warn the other species which can attack them. But scientists have also discovered that these frogs display a signal which is otherwise unknown. Under ultraviolet light, they glow as bright blue. The findings were published in Scientific Reports.

The pumpkin toadlets reside in moist tropical and subtropical forests. As their ears are not developed properly, these frogs are deaf to the mating calls of their own species. Currently, they are the only known species that are deaf to mating calls. While investigating this, scientists accidentally discovered the glowing patterns in two species, Brachycephalus ephippium and  Brachycephalus pitanga.

When observed under natural light, they appear as orange, red or yellow. But when put under UV light, several blue patterns came up on head, back and legs of the toadlets. This is known as fluorescence and it is very rare in vertebrate animals which reside on the land. Scientists are still not sure how fluorescence helps these frogs. It may help them in identifying attackers from beforehand, take preventive actions or identify prospective partners for reproduction.

Fluorescence differs from bioluminescence, in which the body of the animals produces light with the help of chemical reactions. But fluorescence will not function in total darkness as in fluorescence, light is absorbed by some specific molecules and then it is emitted at larger wavelengths, such as red or green which finally creates a glow.

Animals which display fluorescence are corals, scorpions and sea turtle. Scientists also discovered in 2018, that chameleons also show fluorescence. Besides this, another team of researchers found out that two species of a tree frog found in South America have fluorescent skin. But in case of the frogs, the glow originates from the bones similar to that of chameleons.

Researchers observed through chemical analysis that the bony plates which were located on the head and back of the toadlets were very fluorescent. The cells which exhibit fluorescence are also called fluorescent chromatophores. They contain pigments called fluorosomes which contain proteins that are activated with the help of potassium ions. The fluorescent patterns arise from the motion and aggregation of these pigments within the chromatophore.

It is still not known clearly how do the toads use fluorescence for their benefit. It may serve as a warning sign to animals about the toxic nature of the skin as some birds can detect fluorescence in natural light. It can also be used for communication among themselves, as the toads lack the middle ear so they cannot hear calls from their own species.