Hi, it’s Stephen Wolfing, science expert at the Greenygrey. I saw a fascinating story today about how smalleye pygmy sharks use hormones to make cells glow, enabling them to hide from predators. It reminded me of the Greenygrey ability to chameleonise… especially as they’re a type of dogfish! Here’s an account in the Huffington Post:
The researchers… suggest sharks evolved this ability from an ancient organism that would have used these hormones to change their skin pigmentation from light to dark (or vice versa) as a form of camouflage. So while melatonin would’ve lightened the skin of this predecessor, prolactin would have darkened it. Today, these hormones would work as a type of pigment shade, either moving the pigment cells in front of the light-emitting organs (covering them up) or retracting them to expose the glow. Essentially, the sharks now regulate their bioluminescence by changing the degree of pigmentation covering the photophores.
In the smalleye pygmy shark, prolactin pulls the pigment shade over the photophores to dim the glow, while lantern sharks seem to have co-opted this mechanism to produce brighter and shorter bursts of light for communication. As such, Claes and his colleagues suggest the pygmy shark is more closely related to this ancestor than the lantern shark.
“This study is really interesting because it suggests the pygmy shark to be the missing link in the evolution of luminescence in sharks,” Claes told LiveScience.