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

Abstract

Compound eyes of the stomatopod, Gonodactylus oerstedii, exhibit pupillary reflection responses which arise from migration of retinular cell pigment granules. In the light, reflectance from the eye increases as pigment granules accumulate around light-sensitive rhabdoms and scatter incoming light back out of the eye (pupillary closure). At dark onset, reflectance diminishes as pigment granules disperse centrifugally, enhancing photon capture by the rhabdom. We investigated the mechanisms of the pupillary response in intact animals by measuring reflectance from the eye under different temperature conditions. Lowering the temperature from 27° to 7 °C caused an increase in reflectance of infrared light in the absence of visible-light stimuli, indicating pupillary closure. When given light stimuli as temperature decreased, the eye continued to produce reflection increases which decreased in amplitude as the between stimulus reflectance level increased. All low-temperature effects were reversed when temperature was increased to normal. The rate of pupillary closure was insensitive to temperature, with a temperature quotient (Q₁₀) of 0.8 ± 0.1 s.e.m, while pupillary opening was extremely temperature sensitive (Q₁₀ of 5.4 ± 0.4). Different temperature sensitivities for pupillary opening and closing suggest that these processes involve different mechanisms.