Working with Jérôme Mallefet, they explored the possibility that this shark shared its ancestry with the lantern shark, which also employs similar luminescence. They teamed up with Hsuan-Ching Ho from the National Dong Hwa University, Taiwan, the team collected samples of the shark's skins and injected them with different substances including neurotransmitters and hormones and studied the effect. The team learnt that the hormone melatonin, which stimulates light production in lantern sharks - resulted in a glow whereas neurotransmitters which cause light in deep-sea bony fish, did not impact the pygmy at all. The hormone prolactin - threw up some interesting information. It did not cause the shark's 30-minute-long bursts of light (which it does for lantern sharks) but rather dimmed its glow. Claes said this revealed that pygmy sharks use bioluminescence only for camouflage whereas lantern sharks use it to communicate, regulating prolactin to do so. They also concluded that both sharks inherited their bioluminescence from an ancient predecessor which probably employed melatonin to lighten its skin and prolactin to darken it.
Published in Sanctuary Asia, Vol XXXII No. 3, 2012
