Abstract
Like their diurnal relatives, Megalopta genalis use visual information to control flight. Unlike their diurnal relatives, however, they do this at extremely low light intensities. Although Megalopta has developed optical specializations to increase visual sensitivity, theoretical studies suggest that this enhanced sensitivity does not enable them to capture enough light to use visual information to reliably control flight in the rainforest at night. It has been proposed that Megalopta gain extra sensitivity by summing visual information over time. While enhancing the reliability of vision, this strategy would decrease the accuracy with which they can detect image motion—a crucial cue for flight control. Here, we test this temporal summation hypothesis by investigating how Megalopta's flight control and landing precision is affected by light intensity and compare our findings with the results of similar experiments performed on the diurnal bumblebee Bombus terrestris, to explore the extent to which Megalopta's adaptations to dim light affect their precision. We find that, unlike Bombus, light intensity does not affect flight and landing precision in Megalopta. Overall, we find little evidence that Megalopta uses a temporal summation strategy in dim light, while we find strong support for the use of this strategy in Bombus.
Highlights
As light intensities fall, visual information becomes increasingly unreliable and nocturnal animals compensate for this by having eyes that are extremely sensitive to light (Warrant, 2008a,b)
In contrast to Megalopta, the ground speed of Bombus flying at higher light intensities of 190 or 19 lux was significantly affected by light intensity, the absolute lateral position and the variance in lateral position was not
We investigate the effect of light intensity on flight control and landing in a nocturnal (Megalopta) and diurnal (Bombus) bee species
Summary
Visual information becomes increasingly unreliable and nocturnal animals compensate for this by having eyes that are extremely sensitive to light (Warrant, 2008a,b). The nocturnal neotropical sweat bee Megalopta genalis, which relies heavily on visual information to control flight (Baird et al, 2011) and locate its nest stick (Warrant et al, 2004) in dim light, possesses apposition compound eyes How are these insects able to see at night? Megalopta elevate their photon capture by having unusually wide, light-sensitive rhabdoms, and very large facet lenses (Warrant et al, 2004; Greiner et al, 2004a) This increases the sensitivity of their eyes quite significantly, theoretical calculations indicate that it does not allow them to capture enough light to reliably control flight and to locate a small nest stick under the dense rainforest canopy at night (Warrant et al, 2004; Greiner et al, 2004a).
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