Temporal Changes in the Ommatidial Structure of the Cockroach, Leucophaea Maderae

A circadian rhythm in eye sensitivity to light has been previously reported for Leucophaea maderae. Temporal changes in eye cell morphology that could be correlated with those changes in eye sensitivity to light were examined. Rhabdom area, screening pigment organization and palisade layer area about the rhabdom were the parameters measured to detect structural change through time. Measurements of those parameters from tissue samples obtained from the anterior one-third of compound eyes surgically removed at midday, light offset, midnight and light onset from roaches entrained to a 12-h light / 12-h dark photoperiodic cycle were used to assess the daily pattern of morphological changes. Eyes were removed at subjective midday and subjective midnight from roaches free-running under constant conditions of temperature and darkness to detect circadian changes. All roaches received food and water ad libitum. Tissue samples were fixed, embedded, sectioned and the sections were examined and photographed using a Zeiss transmission electron microscope to test for time-related morphological differences. The extent of pigment organization was determined by counting the number of pigment granules found within a 10µm diameter circle centered about the rhabdom. The rhabdom area and the palisade layer area were determined by the Jandel PC3-D computer program. The rhabdom area did not vary throughout the day. The organization of screening pigment granules and the palisade layer area did vary on a daily basis. In animals maintained under constant environmental conditions the rhythm of the organization of the pigment granules did not persist. In contrast, temporal changes in the palisade layer area did persist for three cycles with a pattern similar to that in roaches held under LD12:12 and thus could be considered a circadian rhythm controlled by a pacemaker