Investigations of pigment granule transport systems in Gonodactylus oerstedii (Crustacea: Hoplocarida: Stomatopoda)

Abstract

Pigment granules within retinular cells of the stomatopod crustacean, Gonodactylus oerstedii, undergo rapid, radial migrations in response to changes in ambient lighting. Light stimulates centripetal migration of pigment granules towards the microvillar rhabdomeres where they absorb and scatter incoming light, analogous in function to the closure of a pupil. In the dark, pigment granules disperse centrifugally away from rhabdoms, thereby opening the pupil. Two populations of microtubules in retinular cells of G. oerstedii are appropriately oriented for participation in pigment granule migration. We investigated the possibility that microtubules are involved in pigment granule migration by subjecting animals to low temperature (which can depolymerize some microtubules) and determining the effects of low temperature on pigment granule position and microtubule density within retinular cells. When temperature was decreased, pigment granules in previously dark-adapted eyes aggregated around rhabdoms, in the light-adapted configuration. Lowering the temperature also decreased the density of palisade microtubules, which extend longitudinally in retinular cells along the subrhabdomeric palisade vacuole. These changes reversed when temperature increased. We present a model for pigment granule migration based on the idea that the position of pigment granules in retinular cells is dependent upon the presence of intact palisade microtubules.