Abstract
Insects face the challenge of navigating to specific goals in both bright sun-lit and dim-lit environments. Both diurnal and nocturnal insects use quite similar navigation strategies. This is despite the signal-to-noise ratio of the navigational cues being poor at low light conditions. To better understand the evolution of nocturnal life, we investigated the navigational efficiency of a nocturnal ant, Myrmecia pyriformis, at different light levels. Workers of M. pyriformis leave the nest individually in a narrow light-window in the evening twilight to forage on nest-specific Eucalyptus trees. The majority of foragers return to the nest in the morning twilight, while few attempt to return to the nest throughout the night. We found that as light levels dropped, ants paused for longer, walked more slowly, the success in finding the nest reduced and their paths became less straight. We found that in both bright and dark conditions ants relied predominantly on visual landmark information for navigation and that landmark guidance became less reliable at low light conditions. It is perhaps due to the poor navigational efficiency at low light levels that the majority of foragers restrict navigational tasks to the twilight periods, where sufficient navigational information is still available.
Highlights
Insects are active at different times of the day
Did the late ants appear to walk more slowly, they stopped more frequently compared to the early foragers (Figure 2a; blue circles along each path). This indicated that navigational efficiency of M. pyriformis may suffer at low light
We asked whether the navigational efficiency of animals changes at different light conditions
Summary
The light intensity is nearly 6–11 orders of magnitude dimmer than in the day [1] To cope with this dramatic change in light intensity insects require distinct visual adaptations. Nocturnal hymenopteran insects (e.g., ants, bees, wasps) have apposition eyes, where light reaches the rhabdom through a single lens, being less sensitive compared to the superposition eyes To overcome this reduced sensitivity, nocturnal hymenopterans increase their optical sensitivity by having larger lenses and wider photoreceptors compared to their diurnal relatives [1,5,6,7,8,9,10,11]. Insects that are active in a wide range of ambient light levels cope with the variation in light intensities to some extent by increasing or decreasing the sensitivity of their visual system through pupillary mechanism [12]
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