IV.2 The Design ofCompound Eyes and the
Illumination of Natural Habitats
Eric J. Warrant
Department of Zoology, University of Lund, Helgonavagen 3, S-22362 Lund,
Sweden
Abstract
Compound eyes are the most abundant eye design in the animal kingdom, and
probably its most adaptable. In this chapter I describe the ways in which compound
eyes have evolved in response to the intensity and direction of natural illumination.
Species active in bright light generally have no need for compound eyes of high
sensitivity. Instead, their eyes frequently possess acute zones, regions where spatial
resolution is greatly enhanced, and where the spatial layout of ommatidia is often
matched to the spatial layout of the habitat. Such matched filtering is not confmed to
habitat structure. Acute zones may also behave as matched filters for an animal's
motion flow-field or for localizing other animals. In dim light, sensitivity becomes
the overriding priority, and at night, or in the depths of sea, compound eyes of
immense sensitivity have evolved. Those from increasing depths in the sea also tend
to have an increasingly dorsal bias that reflects the dominance of dorsal (downwelling) illumination. These and other aspects of compound eye design are illustrated
using a broad range of aquatic and terrestrial invertebrates as examples.
Key words Compound eye, light intensity, matched filter, resolution, sensitivity
1 Introduction
The daylight seen by a butterfly flitting across a sunny meadow is 15 orders of
magnitude brighter than that seen by a crustacean swimming I km below the surface
of the sea. Both of these animals have compound eyes optimized for vision at these
extremes, and both require their eyes to survive. Of course, no single eye is able to
see over this entire range. Instead, butterfly eyes are designed for vision in bright
daylight, and for a range of intensities a few o;-ders of magnitude lower than this, in
an extended world of contrast features. Deep sea crustaceans, on the other hand, have
compound eyes designed for seeing in a world where dim blue daylight comes from a
small angle directly above, and where the darkness in other directions can be pierced
by bright pin-points of bioluminescence. How have these two extreme habitats - and
indeed all others between them - shaped the design of compound eyes?
The most obvious and dramatic effect has been the evolution of two broad optical
classes of compound eyes. One class- apposition eyes (Fig. IA)- is adapted best to
Illumination of Natural Habitats
Eric J. Warrant
Department of Zoology, University of Lund, Helgonavagen 3, S-22362 Lund,
Sweden
Abstract
Compound eyes are the most abundant eye design in the animal kingdom, and
probably its most adaptable. In this chapter I describe the ways in which compound
eyes have evolved in response to the intensity and direction of natural illumination.
Species active in bright light generally have no need for compound eyes of high
sensitivity. Instead, their eyes frequently possess acute zones, regions where spatial
resolution is greatly enhanced, and where the spatial layout of ommatidia is often
matched to the spatial layout of the habitat. Such matched filtering is not confmed to
habitat structure. Acute zones may also behave as matched filters for an animal's
motion flow-field or for localizing other animals. In dim light, sensitivity becomes
the overriding priority, and at night, or in the depths of sea, compound eyes of
immense sensitivity have evolved. Those from increasing depths in the sea also tend
to have an increasingly dorsal bias that reflects the dominance of dorsal (downwelling) illumination. These and other aspects of compound eye design are illustrated
using a broad range of aquatic and terrestrial invertebrates as examples.
Key words Compound eye, light intensity, matched filter, resolution, sensitivity
1 Introduction
The daylight seen by a butterfly flitting across a sunny meadow is 15 orders of
magnitude brighter than that seen by a crustacean swimming I km below the surface
of the sea. Both of these animals have compound eyes optimized for vision at these
extremes, and both require their eyes to survive. Of course, no single eye is able to
see over this entire range. Instead, butterfly eyes are designed for vision in bright
daylight, and for a range of intensities a few o;-ders of magnitude lower than this, in
an extended world of contrast features. Deep sea crustaceans, on the other hand, have
compound eyes designed for seeing in a world where dim blue daylight comes from a
small angle directly above, and where the darkness in other directions can be pierced
by bright pin-points of bioluminescence. How have these two extreme habitats - and
indeed all others between them - shaped the design of compound eyes?
The most obvious and dramatic effect has been the evolution of two broad optical
classes of compound eyes. One class- apposition eyes (Fig. IA)- is adapted best to