196
D
v
female
D
B
v
male
L
L
Eric]. Warrant
Fig. 3A,B Sexual dimorphism in the
apposition eyes of the hoverfly
Volucella pellucens. A Female. B Male.
The visual fields of the left eyes of the
two sexes, and interommatidial angles
shown by isolines, are projected onto
spheres. Terminology and conventions
as in Fig. 2. Both sexes possess acute
zones directed frontally, an adaptation
for processing optical flow during
forward flight (see Sect. 3.1.3) .
Compared to the female however, the
male has a much larger acute zone
directed 20°-30° dorsally (shaded
regions, where df/J < 1.1 °). The male's
acute zone is used for fixating females
during sexual pursuit. (Warrant and
Olsson, unpubl. data)
identified large male-specific visual
cells that respond maximally to
small dark objects that move across
a bright background in the frontaldorsal visual field. This seems to
be an excellent matched filter for
silhouetted females flying against
the sky!
Similar cells are also found in
the dragonfly brain, not for spotting
females, but for spotting prey.
These insects have possibly the
most advanced dorsal acute zones
of all apposition eyes (Fig. 4), with
values of L1rp falling to an incredibly low 0.24° in Anax junius
(Sherk 1978). The facet diameters
here are huge (62 Jlm) and this,
together with a yellow screening
pigment between the ommatidia
(which is transparent to the light
which reconverts rhodopsin:
Labhart and Nilsson 1995), helps to ensure high sensitivity. The acute zone, clearly
visible even to our own naked eye (Fig. 4A), has its region of highest resolution
distributed in an elongated dorsal strip (Fig. 4B). Just as in male flies, this region
eventually feeds its high resolution and sensitivity to large specialized cells in the
brain, which behave as matched filters for fly-sized objects against a bright background
(Fig. 4C; Olberg 1981, 1986).
D
v
female
D
B
v
male
L
L
Eric]. Warrant
Fig. 3A,B Sexual dimorphism in the
apposition eyes of the hoverfly
Volucella pellucens. A Female. B Male.
The visual fields of the left eyes of the
two sexes, and interommatidial angles
shown by isolines, are projected onto
spheres. Terminology and conventions
as in Fig. 2. Both sexes possess acute
zones directed frontally, an adaptation
for processing optical flow during
forward flight (see Sect. 3.1.3) .
Compared to the female however, the
male has a much larger acute zone
directed 20°-30° dorsally (shaded
regions, where df/J < 1.1 °). The male's
acute zone is used for fixating females
during sexual pursuit. (Warrant and
Olsson, unpubl. data)
identified large male-specific visual
cells that respond maximally to
small dark objects that move across
a bright background in the frontaldorsal visual field. This seems to
be an excellent matched filter for
silhouetted females flying against
the sky!
Similar cells are also found in
the dragonfly brain, not for spotting
females, but for spotting prey.
These insects have possibly the
most advanced dorsal acute zones
of all apposition eyes (Fig. 4), with
values of L1rp falling to an incredibly low 0.24° in Anax junius
(Sherk 1978). The facet diameters
here are huge (62 Jlm) and this,
together with a yellow screening
pigment between the ommatidia
(which is transparent to the light
which reconverts rhodopsin:
Labhart and Nilsson 1995), helps to ensure high sensitivity. The acute zone, clearly
visible even to our own naked eye (Fig. 4A), has its region of highest resolution
distributed in an elongated dorsal strip (Fig. 4B). Just as in male flies, this region
eventually feeds its high resolution and sensitivity to large specialized cells in the
brain, which behave as matched filters for fly-sized objects against a bright background
(Fig. 4C; Olberg 1981, 1986).