Abstract
BackgroundIn the permanent daylight conditions north of the Arctic circle, there is a unique opportunity for bumblebee foragers to maximise intake, and therefore colony growth, by remaining active during the entire available 24-h period. We tested the foraging rhythms of bumblebee (Bombus terrestris and B. pascuorum) colonies in northern Finland during the summer, when the sun stays above the horizon for weeks. We used fully automatic radio-frequency identification to monitor the foraging activity of more than 1,000 workers and analysed their circadian foraging rhythms.ResultsForagers did not use the available 24-h foraging period but exhibited robust diurnal rhythms instead. A mean of 95.2% of the tested B. terrestris workers showed robust diurnal rhythms with a mean period of 23.8 h. Foraging activity took place mainly between 08:00 and 23:00, with only low or almost no activity during the rest of the day. Activity levels increased steadily during the morning, reached a maximum around midday and decreased again during late afternoon and early evening. Foraging patterns of native B. pascuorum followed the same temporal organisation, with the foraging activity being restricted to the period between 06:00 and 22:00.ConclusionsThe results of the present study indicate that the circadian clock of the foragers must have been entrained by some external cue, the most prominent being daily cycles in light intensity and temperature. Daily fluctuations in the spectral composition of light, especially in the UV range, could also be responsible for synchronising the circadian clock of the foragers under continuous daylight conditions.
Highlights
In the permanent daylight conditions north of the Arctic circle, there is a unique opportunity for bumblebee foragers to maximise intake, and colony growth, by remaining active during the entire available24-h period
The results of the present study indicate that the circadian clock of the foragers must have been entrained by some external cue, the most prominent being daily cycles in light intensity and temperature
The foraging pattern of the native B. pascuorum colony was similar to the ones observed in the introduced B. terrestris colonies, with the foraging activity being restricted to the period between 06:00 and 22:00 and no recorded activity during the 'night' (Figure 3)
Summary
In the permanent daylight conditions north of the Arctic circle, there is a unique opportunity for bumblebee foragers to maximise intake, and colony growth, by remaining active during the entire available24-h period. In the permanent daylight conditions north of the Arctic circle, there is a unique opportunity for bumblebee foragers to maximise intake, and colony growth, by remaining active during the entire available. The foraging activity of the workers is synchronized to the available photoperiod by endogenous circadian clocks [4,5]. Given that foragers use the entire available photoperiod in temperate regions, one would expect that they would fully utilise longer or even continuous photoperiods. Full list of author information is available at the end of the article prevailing north of the Arctic Circle during summer to gather as much food as possible and maximise colony growth. We might expect that arctic bumblebees would adapt to the foraging conditions that prevail under the midnight sun
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
