Back in the land (sea?) of bioluminescence, a recent story on sharks may reveal some evolutionary background for hormonal control of their light emission. These little sharks have a “luminescent liquid” in certain organs, and the main method of reducing the brightness displayed is to cover up the light-emitting cells/organs with melanocytes, which can also be altered in other sharks and rays to aid camouflage. It turns out, though, that different luminescent shark groups use the hormones differently, and the authors have a good guess as to which method is more ancestral.
Some “lantern sharks” luminesce for the same reasons as anglerfish, to attract food sources, and some use their light to camouflage themselves against aquatic predators. The sky is bright, and a dark outline is easily seem from below. (See also Creaturecast on Squid Iridescence.) — KMP
Claes JM, Ho H-C, Mallefet J. 2012. Control of luminescence from pygmy shark (Squaliolus aliae) photophores. J Exp Biol 215:1691-1699.
