Dynamic camouflage by Nassau groupers Epinephelus striatus on a Caribbean coral reef.

This field study describes the camouflage pattern repertoire, associated behaviours and speed of pattern change of Nassau groupers Epinephelus striatus at Little Cayman Island, British West Indies. Three basic camouflaged body patterns were observed under natural conditions and characterized quantitatively. The mean speed of pattern change across the entire body was 4.44 s (range = 0.97-9.87 s); the fastest pattern change as well as contrast change within a fixed pattern occurred within 1 s. Aside from apparent defensive camouflage, E. striatus used camouflage offensively to approach crustacean or fish prey, and three successful predation events were recorded. Although animal camouflage is a widespread tactic, dynamic camouflage is relatively uncommon and has been studied rarely in marine teleosts under natural conditions. The rapid changes observed in E. striatus suggest direct neural control of some skin colouration elements, and comparative studies of functional morphology and behaviour of colour change in other coral-reef teleosts are likely to reveal new mechanisms and adaptations of dynamic colouration.

Pigment granule translocation in red ovarian chromatophores from the palaemonid shrimp Macrobrachium olfersi (Weigmann, 1836): functional roles for the cytoskeleton and its molecular motors.

The binding of red pigment concentrating hormone (RPCH) to membrane receptors in crustacean chromatophores triggers Ca²âº/cGMP signaling cascades that activate cytoskeletal motors, driving pigment granule translocation. We investigate the distributions of microfilaments and microtubules and their associated molecular motors, myosin and dynein, by confocal and transmission electron microscopy, evaluating a functional role for the cytoskeleton in pigment translocation using inhibitors of polymer turnover and motor activity in vitro. Microtubules occupy the chromatophore cell extensions whether the pigment granules are aggregated or dispersed. The inhibition of microtubule turnover by taxol induces pigment aggregation and inhibits re-dispersion. Phalloidin-FITC actin labeling, together with tannic acid fixation and ultrastructural analysis, reveals that microfilaments form networks associated with the pigment granules. Actin polymerization induced by jasplaquinolide strongly inhibits RPCH-induced aggregation, causes spontaneous pigment dispersion, and inhibits pigment re-dispersion. Inhibition of actin polymerization by latrunculin-A completely impedes pigment aggregation and re-dispersion. Confocal immunocytochemistry shows that non-muscle myosin II (NMMII) co-localizes mainly with pigment granules while blebbistatin inhibition of NMMII strongly reduces the RPCH response, also inducing spontaneous pigment dispersion. Myosin II and dynein also co-localize with the pigment granules. Inhibition of dynein ATPase by erythro-9-(2-hydroxy-3-nonyl) adenine induces aggregation, inhibits RPCH-triggered aggregation, and inhibits re-dispersion. Granule aggregation and dispersion depend mainly on microfilament integrity although microtubules may be involved. Both cytoskeletal polymers are functional only when subunit turnover is active. Myosin and dynein may be the molecular motors that drive pigment aggregation. These mechanisms of granule translocation in crustacean chromatophores share various features with those of vertebrate pigment cells.