Teeny tiny glowing sharks could be missing link

Take a tour of sharks around the oceans and you’ll find that around one in ten has the ability to glow, sparkle and twinkle its own eerie light. Some of the tiniest and most mysterious sharks – the pygmy and lantern sharks – are the subject of a new study looking into how glowing sharks evolved.

Smalleye pygmy sharks are tiny, stealth torpedoes – they only grow up to 8 inches (22cm) and with glowing bellies, camouflage their silhouette from beneath to blend in with the brighter sea above.

Julien Claes and colleagues have figured out that pygmy sharks use a hormone, prolactin, to dim their lights. Meanwhile their cousins – the velvet belly lantern sharks – use the same hormone to flicker their lights and communicate to other sharks in the dark depths. A second hormone, melatonin, controls their overall brightness.

The team theorize that the first glowing sharks used prolactin as the pygmy sharks do today, as a simple on-off switch. Then the more complex mode of controlling their glittering lights, as seen in lantern sharks today, came later.

Just goes to show what a neat bunch of animals sharks are.

Check out Claes et al’s paper (abstract) in the Journal of Experimental Biology.

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