Except the night owls, most humans tend to stay active during the day and rest to recharge during the night. Similarly, most animal species are adapted to be active during specific periods of the day and these activity periods make up their temporal niche. Temporal niches are controlled by biological clocks and environmental cues such as light, humidity and temperature. Animals are limited to these niches due to both internal (like physiology and sensory capacities) and external (like predation and resource availability) factors. As a college student, I wish I needed less sleep and could enjoy more of a nightlife than what I can currently afford. Unlike me, Apis dorsata, the giant honey bee, has an exceptional ability to stay active both during the day and night!
The Giant Honey Bee (from Wikimedia Commons)
Some of its anatomical and physiological characteristics can help us understand this phenomenon. The giant honey bee is the second largest honey bee, which also means that it has very large compound eyes that provide greater visual sensitivity. In addition, the simpler and light-sensitive eyes called ocelli are more prominent in this species, enhancing light sensitivity.
There is also evidence that its visual sensory system is able to capture and integrate light from wide areas of its visual field, allowing it to see better in moonlight. Even though the giant honey bee does not possess as much visual sensitivity as other nocturnal bee species, it is likely that its visual adaptations are key for its ability to stay active at night.
A Bee Head
Integrative Biologist Allison Young and her team recently investigated nocturnal activity in the giant honey bees that live in the outskirts of the city of Bangalore, India. They tested if the illumination from the moon or artificial city lights allowed the bees to stay active during the night. They also investigated the effects of seasons, lunar cycles and temperature on the nocturnal behavior. To measure activity, the scientists counted bees arriving to the nest per unit time (arrival rate). They confidently assumed that the arrivals of bees were an indication of a return after successful foraging because their data convincingly showed that these recorded arrivals were accompanied by the bees’ typical post-foraging dance.
They found that bee arrival rate increased positively with illumination at all times of the day (daytime, twilight and nighttime). Additionally, the arrival rate at night was significantly higher within a week of the full moon than other phases of the lunar cycle. This finding solidifies previous suggestions that the giant honey bee forages on a bright moonlit night.
Nocturnal activity at different times of the day across different phases of the lunar cycle.
Light availability was found to be the key for nighttime foraging. Artificial city light added some illumination at the study site but did not significantly impact total illumination, as the results were found to be consistent with previous reports of nocturnal activity in this bee.
Arrival rates during twilight hours (when moonlight is absent) were overall greater than other times of the day. One explanation could be that there is less competition during the twilight hours so it is beneficial for the bees to extend their daytime foraging into twilight hours to exploit more resources, or it could be due to illumination by the artificial city lights. The scientists also found evidence that the urban light is enough for some foraging activity at night even when the moon was not present.
There was a higher nighttime arrival rate than in daytime during winter than in spring or summer. The seasonal shifts may be due to changes in resource availability. There was no effect of nighttime foraging on daytime foraging, suggesting that nocturnal activity is not the result of shifting biological clocks (since daily activity patterns did not shift) and instead is affected directly by the lunar cycle. This further strengthens the idea of light affecting activity positively. Illumination from the environment causes only the temporal niche to shift. Temperature was found to have no significant effect on bee arrival rate. It could be that the lowest temperature in Bangalore was warm enough to allow the bees to maintain warm body temperatures during flight.
While these bees are found in a variety of habitats including forests, they only studied the city bees so the results cannot be generalized without extensive future work. However, they convincingly concluded that the giant honey bee should also be considered a cathemeral species (one who is able to forage both during the day and night) when there is sufficient illumination. Since this is the first systematic study on the nocturnal behavior of these bees, it is an excellent starting point for future work on this topic. It would be interesting to next explore the relationship between nocturnal activity and genes responsible for setting up biological clocks to explain the underlying mechanisms and further clarify if the nocturnal activity is due to effects of direct light or a shift in biological clocks.
Reference: Young, A. M., Kodabalagi, S., Brockmann, A., & Dyer, F. C. (2021). A hard day’s night: Patterns in the diurnal and nocturnal foraging behavior of Apis dorsata across lunar cycles and seasons. PLOS ONE, 16(10), e0258604. https://doi.org/10.1371/journal.pone.0258604
