Daily Changes in Ultraviolet Light Levels Can Synchronize the Circadian Clock of Bumblebees (Bombus terrestris)

Abstract

Endogenous circadian clocks are synchronized to the 24-h day by external zeitgebers such as daily light and temperature cycles. Bumblebee foragers show diurnal rhythms under daily light:dark cycles and short-period freerunning circadian rhythms in constant light conditions in the laboratory. In contrast, during the continuous light conditions of the arctic summer, they show robust 24-h rhythms in their foraging patterns, meaning that some external zeitgeber must entrain their circadian clocks in the presence of constant light. Although the sun stays above the horizon for weeks during the arctic summer, the light quality, especially in the ultraviolet (UV) range, exhibits pronounced daily changes. Since the photoreceptors and photopigments that synchronize the circadian system of bees are not known, we tested if the circadian clocks of bumblebees (Bombus terrestris) can be entrained by daily cycles in UV light levels. Bumblebee colonies were set up in the laboratory and exposed to 12 h:12 h UV + : UV− cycles in otherwise continuous lighting conditions by placing UV filters on their foraging arenas for 12 h each day. The activity patterns of individual bees were recorded using fully automatic radiofrequency identification (RFID). We found that colonies manipulated in such a way showed synchronized 24-h rhythms, whereas simultaneously tested control colonies with no variation in UV light levels showed free-running rhythms instead. The results of our study show that bumblebee circadian rhythms can indeed be synchronized by daily cycles in ambient light spectral composition. (Author correspondence: r.stanewsky@qmul.ac.uk)

The impact of artificial light at night on nocturnal insects: A review and synthesis

“…If ALAN is sufficiently intense and/or sustained in time, and of a specific spectral composition, it can desynchronize the internal clock (reviewed by Saunders, ). For example, the pink bollworm Pectinophora gossypiella can be artificially entrained by monochromatic yellow light emitted by low‐pressure sodium (LPS) lamps (Pittendrigh & Minis, ), and diurnal Bombus terrestris bumblebees by UV illumination (Chittka , Stelzer, & Stanewsky, ). Desynchronization reduces reproductive fitness of Drosophila melanogaster fruit flies (Xu, DiAngelo, Hughes, Hogenesch, & Sehgal, , see also McLay, Nagarajan‐Radha, Green, & Jones, ) and has the potential to disrupt vital biological processes in other taxa (Dominoni, Borniger, & Nelson, ; Gaston et al, ; Saunders, ).…”

“…If ALAN is sufficiently intense and/or sustained in time, and of a specific spectral composition, it can desynchronize the internal clock (reviewed by Saunders, 2012). For example, the pink bollworm Pectinophora gossypiella can be artificially entrained by monochromatic yellow light emitted by low-pressure sodium (LPS) lamps (Pittendrigh & Minis, 1971), and diurnal Bombus terrestris bumblebees by UV illumination (Chittka , Stelzer, & Stanewsky, 2013).…”

Peer Review #2 of "Orb-weaving spiders are fewer but larger and catch more prey in lit bridge panels from a natural artificial light experiment (v0.1)"

“…Exposure to ALAN can alter circadian rhythms (Chittka, Stelzer & Stanewsky, 2013), inhibit reproduction (Bebas, Cymborowski & Giebultowicz, 2001;Van Geffen et al, 2015), accelerate PeerJ reviewing PDF | (2019:12:43622:2:0:NEW 24 Feb 2020)…”

Entraining to the polar day: circadian rhythms in arctic ground squirrels

“…In invertebrates, it has long been postulated that persistent daily rhythms of behavior may indicate a circadian clock that is entrained to diel changes in temperature or UV light (Nordtug and Melø, 1988). In bumblebees, daily rhythms of behavior persist in the Arctic (Stelzer and Chittka, 2010), and captive experiments suggest they are capable of entraining to cycles in UV radiation (Chittka et al, 2013). However, Antarctic midges do not exhibit rhythmic oscillations of clock genes despite the persistence of daily behavioral rhythms under the midnight sun (Kobelkova et al, 2015).…”