The effects of light and temperature on the structural organization of the eye of the Antarctic amphipod Orchomene plebs (Crustacea)

• Published in: Proceedings of the Royal Society of London. Series B. Biological Sciences
• Format: Article in Journal/Newspaper
• Language: English
• Published: The Royal Society 1979
• Subjects: Antarctic; Cones The; Cones, The; The Antarctic; The Cones; Antarc*
• Online Access: http://dx.doi.org/10.1098/rspb.1979.0110; https://royalsocietypublishing.org/doi/pdf/10.1098/rspb.1979.0110

The Antarctic amphipod Orchomene plebs lives in an environment which is characterized by stable temperatures of — 2 to 0 °C, and low ambient light intensities. The microanatomy of the eye of dark adapted and light-adapted animals, kept at 0 °C, was studied by light and electron micro­scopy and compared with that of individuals kept at + 10 °C for 7 h. The eye of a 19 mm (total body length) specimen consists of approxi­mately 260 ommatidia, each measuring 40-50 μm across. The cornea is smooth and external facets are not developed. The crystalline cones, which are the intracellularly secreted products of two cone cells per ommatidium, possess cores that stain more intensely than their peripheral regions. The ultrastructure of the core reveals a regular lattice of 30 nm particles, which are interpreted as glycogen granules. The rhabdom, whose microvilli measure 85-100 nm in diameter, is spindle-shaped and of the centrally fused type. The ratio of rhabdom length: width is 3.2 in light- adapted and 2.8 in dark-adapted animals. There are five retinula cells per omma, one of them being consistently smaller than the rest. Spherical (0.4 μm) granules of screening pigment, present only in the five retinula cells, exhibit migrations that are not controlled by an internal rhythm but are the direct response to fluctuations in the ambient light intensity. In the light-adapted state the pigment grains form a sleeve around the entire rhabdom, but in the dark-adapted eye they cluster around the proximal ends of the cones. The nuclei of the retinula cells are found below the basement membrane, but those of the cells occupying the spaces between ommatidial groups are located above it. These ‘inter­stitial’ cells lack pigment granules, but contain many vesicular organelles, which in the dark-adapted state only resemble miniature sea-urchins of 0.4 μm diameter. Heat-stressed dark-adapted animals exhibit grotesquely deformed rhabdoms with microvilli whose membranes are severely disrupted. The position of the screening pigment is ...