A 24-Hour Cycle in Single Locust and Mantis Photoreceptors

Abstract

When fixed during the night the rhabdom of the locust and mantis is much broader than when fixed during the day. Dark-adapted ommatidia of the locust and mantis by day and night have a zone of vacuoles around the rhabdom tip, but when light-adapted this zone is replaced by cytoplasm rich in mitochondria. Illumination of the rhabdom in the night state causes the microvilli to swell and the rhabdom to break down over the course of about 1 h. A diurnal rhythm is apparent in the spontaneous breakdown of the rhabdom in the morning even though the eye has seen no light for 12 h. Intensity/response curves (peak of the response in mV plotted against log intensity of stimulus) show an increase in sensitivity during the night even though the stimulus is a point source on axis. On the other hand, counts of bumps (quantal responses to individual photons) show no change in photon capture efficiency at night when the stimulus is a point source. Strong illumination of the eye in the night state causes a desensitization which continues for 1 h. Measurements of the acceptance angle in the dark-adapted day and night states show that field size is an indicator of the diameter of the rhabdom tip, but actual fields are larger than those calculated from the anatomical dimensions.