Limulus Brain Modulates the Structure and Function of the Lateral Eyes

Abstract

At night efferent optic nerve activity generated by a circadian clock in the Limulus brain changes the structure of the photoreceptor and surrounding pigment cells in the animal's lateral eyes. The structural changes allow each ommatidium to gather light from a wider area at night than during the day. Visual sensitivity is thereby increased, but spatial resolution is diminished. At daybreak efferent activity from the clock stops, the structural changes reverse, and the field of view of each ommatidium decreases. The cyclic changes are endogenous and continue in the dark. Thus, under the control of a circadian clock, the Limulus eye exchanges its daytime acuity for greater sensitivity at night.

Circadian rhythms of behavioral cone sensitivity and long wavelength opsin mRNA expression: a correlation study in zebrafish

“…Circadian gene expression in the pineal photoreceptor cells may provide cues to the retina through centrifugal pathways. Centrifugal modulation of visual sensitivity has been previously reported in Limulus (Barlow et al, 1980;Battelle, 1991) and in zebrafish (Maaswinkel and Li, 2003).…”

A Circadian Clock in the Olfactory Bulb Controls Olfactory Responsivity

“…At the same time, the clock reduces noise in the eye by protonating rhodopsin, increasing its energy of activation (Kaplan et al, 1990;Barlow et al, 1993). The increased sensitivity at night comes at the cost of reduced spatial acuity because each photoreceptor views a larger and overlapping field with its neighbors (Barlow et al, 1980). The benefit is that horseshoe crabs can use vision to find mates equally well day and night (Powers et al, 1991).…”

Brightness discrimination in the day- and night-adapted hunting spider Cupiennius salei

“…Among diurnal species, some Salticidae (jumping spiders) have been investigated: Phanias harfordi and Phidippus johnsoni showed no modification of the rhabdomere architecture (Eakin and Brandenburger, 1971), but in Servaea vestita an exocytotic shedding of the photoreceptor membrane was observed (Blest and Maples, 1979). In the horseshoe crab Limulus polyphemus (Chelicerata) (Chamberlain and Barlow, 1984), a circadian cycle also affects the eyes: the rhabdomeric membrane is only briefly dismantled; furthermore, the aperture of each ommatidium (visual unit of a compound eye) is reduced and the responsiveness of the photoreceptor cells and optic nerves is decreased (Barlow et al, 1980). Neither of these last two mechanisms occurs in C. salei.…”