200
Eric J. Warrant
lateral
dorsal
lateral
anten·or
3.5
D
D
..... 3.0
PCDA
PBA
OJ
u
"'
v
v
~
'" 2.5
OJ
0...
6 2.0
0
"0
..0
"'
~ 1.5
1.0
-------------------60 -40 -20 0 20 40 60 80
-20
0
20
40
60
80
Latitude (deg)
Longitude (de g)
Fig. 6A,B Local acute zones in the retina of the hummingbird hawkmoth Macrog/ossum
stellatarum. These acute zones, not visible from outside the eye, are built by abandoning the
usual ratio of one rhabdom per facet, and instead packing more rhabdoms into the retina. The
number of rhabdoms per facet is shown (A) along the dorso-ventral meridian (longitude 0°),
and (B) along the posterior-anterior equator (latitude 0°). Except for the extreme dorsal (and
possibly the extreme ventral) part of the eye, the number of rhabdoms always exceeds the
number of facets. Note that rhabdom density increases at the equator to form a horizontal
visual streak (A), and that density also increases markedly along the equator towards the front
of the eye to form a frontal acute zone (B). These increases in density are accompanied by
decreases in the inter-receptor angle, which falls to 1.4 ° at the equator in A, and to around I 0
at the front of the eye in B. D dorsal; V ventral; A anterior; P posterior. (From Warrant et al.
1999)
As in flies, the sampling grid dilutes from front to back along the streak, presumably
to match the flow field during forward flight. All of these unusual adaptations produce
an eye of exceptional resolution and sensitivity, with the narrowest photoreceptor
receptive fields yet measured in a superposition eye (ca. 1.3°: Warrant, Bartsch and
Gunther, in prep.)
4 Compound Eyes for Dim Habitats
As night advances, or as one penetrates the depths of the sea, light intensities fall
dramatically. A bright sunny day is more than 100 million times brighter than a
moonless starry night. In the clearest oceans and lakes, light intensity is reduced by
1.5 orders of magnitude for every 100m of depth. At 700 m there would be insufficient
daylight to sustain human vision, and below 1000 m there would be insufficient
daylight to sustain vision of any kind (Denton 1990). The eyes of those animals that
do live at tremendous depths are not designed to see daylight at all, but rather the
point-source bioluminescent flashes produced by other animals, an interesting topic
beyond the scope of this chapter.
Despite the problems of noise and visual uncertainty that accompany dim light, a
rich variety of animals are nocturnal or live in the deep sea. Those with compound
Eric J. Warrant
lateral
dorsal
lateral
anten·or
3.5
D
D
..... 3.0
PCDA
PBA
OJ
u
"'
v
v
~
'" 2.5
OJ
0...
6 2.0
0
"0
..0
"'
~ 1.5
1.0
-------------------60 -40 -20 0 20 40 60 80
-20
0
20
40
60
80
Latitude (deg)
Longitude (de g)
Fig. 6A,B Local acute zones in the retina of the hummingbird hawkmoth Macrog/ossum
stellatarum. These acute zones, not visible from outside the eye, are built by abandoning the
usual ratio of one rhabdom per facet, and instead packing more rhabdoms into the retina. The
number of rhabdoms per facet is shown (A) along the dorso-ventral meridian (longitude 0°),
and (B) along the posterior-anterior equator (latitude 0°). Except for the extreme dorsal (and
possibly the extreme ventral) part of the eye, the number of rhabdoms always exceeds the
number of facets. Note that rhabdom density increases at the equator to form a horizontal
visual streak (A), and that density also increases markedly along the equator towards the front
of the eye to form a frontal acute zone (B). These increases in density are accompanied by
decreases in the inter-receptor angle, which falls to 1.4 ° at the equator in A, and to around I 0
at the front of the eye in B. D dorsal; V ventral; A anterior; P posterior. (From Warrant et al.
1999)
As in flies, the sampling grid dilutes from front to back along the streak, presumably
to match the flow field during forward flight. All of these unusual adaptations produce
an eye of exceptional resolution and sensitivity, with the narrowest photoreceptor
receptive fields yet measured in a superposition eye (ca. 1.3°: Warrant, Bartsch and
Gunther, in prep.)
4 Compound Eyes for Dim Habitats
As night advances, or as one penetrates the depths of the sea, light intensities fall
dramatically. A bright sunny day is more than 100 million times brighter than a
moonless starry night. In the clearest oceans and lakes, light intensity is reduced by
1.5 orders of magnitude for every 100m of depth. At 700 m there would be insufficient
daylight to sustain human vision, and below 1000 m there would be insufficient
daylight to sustain vision of any kind (Denton 1990). The eyes of those animals that
do live at tremendous depths are not designed to see daylight at all, but rather the
point-source bioluminescent flashes produced by other animals, an interesting topic
beyond the scope of this chapter.
Despite the problems of noise and visual uncertainty that accompany dim light, a
rich variety of animals are nocturnal or live in the deep sea. Those with compound