Flight control and landing precision in the nocturnal bee Megalopta is robust to large changes in light intensity

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.

Keywords: Bombus; Megalopta; flight control; light intensity; neural summation.

Figure 1

The experimental apparatus. (A) The experimental tunnel used to investigate the effect of light intensity on flight control in Megalopta and Bombus. Flights from the tunnel entrance to the nest were recorded using a camera mounted underneath the tunnel. (B) The experimental apparatus used to investigate the effect of light intensity on landing in Megalopta and Bombus. Approaches to and landings on the disk were recorded using a camera mounted to the side.

Figure 2

The effect of light intensity on flight control in Megalopta and Bombus. The effect of light intensity on ground speed (A), median lateral position (B), and variance (inter-quartile range) in lateral position (C) of Megalopta (blue stars; 51 flights, 19 individuals, 15 nests—different symbols indicate data from different nests) and Bombus [box plots; 23 flights (19 lux), 28 flights (190 lux), ~20 individuals] flying along an experimental tunnel (140 mm wide) at different light intensities. The boxes indicate the 25–75% quartile of the data, the red line indicates the median and the whiskers show the extent of the data. Gray lines indicate a linear regression analysis of the Megalopta data; details of the analysis and the statistical comparison (F-value) against a constant model are provided in each plot.

Figure 3

The effect of light intensity on the timing of leg extension when landing in Megalopta and Bombus. (A) The effect of light intensity on the time between leg extension and contact (TC) with a concentric ring pattern (inset) in Megalopta (blue stars, 27 landings, 10 individuals, 4 nests—different symbols indicate data from different nests) and Bombus [box plots, details as in Figure 1; 21 landings (19 lux), 37 landings (190 lux), ~20 individuals]. (B) The effect of visual expansion cues on TC in Megalopta [ring pattern (inset): 27 landings, radial pattern (inset): 34 landings]. Box plot details as in Figure 1 indicate the distance between the lower and upper quartile values, red lines indicate the median, whiskers indicate the entire spread of the data and red crosses indicate outliers. (C) The effect of light intensity on TC for a natural nest stick (inset) in Megalopta (23 landings, 4 individuals, 2 nests—different symbols indicate data from different nests). Gray lines indicate a linear regression analysis of the Megalopta data; details of the analysis and the statistical comparison (F-value) against a constant model are provided in each plot.