Rapid integumental color changes due to novel iridophores in the chameleon sand tilefish Hoplolatilus chlupatyi.

The wavelength of the light reflected from iridophores depends on the thickness and the spacing of intracellular reflecting platelets. Here, we show that the rapid color change from blue to red of the chameleon sand tilefish Hoplolatilus chlupatyi is mediated by adrenergic stimulation of a novel type of iridophore in which reflecting platelets are concentrated selectively in the periphery of the cell, near the plasma membrane. The color changes are not only observed in vivo but also in pigment cells of isolated scales which respond to increases in K ion concentrations in 0.5 s and to addition of norepinephrine within 1 s. The norepinephrine effect can be blocked by addition of the alpha-adrenergic antagonist phentolamine. The results suggest that adrenergic stimulation leads to changes in reflecting platelet organization in Hoplolatilus chlupatyi iridophores and represents the major mediator of the rapid color change in this fish in vivo.