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Fig. 6. Adaptations for nocturnal vision in the photoreceptors of the nocturnal
sweat bee Megalopta genalis, as compared to photoreceptors in the
closely related diurnal sweat bee Lasioglossum leucozonium. (A,B)
Responses to single photons (or `photon bumps': arrowheads) recorded from
photoreceptors in Megalopta (A) and Lasioglossum (B). Note
that the bump amplitude is larger, and the bump time course much slower, in
Megalopta than in Lasioglossum. (C–F) Average contrast
gain as a function of temporal frequency in Megalopta (blue curves,
N=8 cells) and Lasioglossum (red curves, N=8 cells)
at different adapting intensities, indicated as `effective photons' per second
in each panel for each species [for each species, each stimulus intensity was
calibrated in terms of `effective photons'; that is, the number of photon
bumps per second the light source elicited, thereby eliminating the effects of
differences in the light-gathering capacity of the optics between the two
species, which is about 27 times
(Lillywhite and Laughlin,
1979)]. In light-adapted conditions (C,D), the two species reach
the same maximum contrast gain per unit bandwidth although
Lasioglossum has a broader bandwidth and a higher corner frequency
(the frequency at which the gain has fallen off to 50% of its maximum). In
dark-adapted conditions (E,F), Megalopta has a much higher contrast
gain per unit bandwidth. All panels adapted with kind permission from
Frederiksen et al. (Frederiksen et al.,
2008).
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