Abstract
Circadian clocks are synchronized with the external environment by light and temperature. The effect of these cues on behavior is well-characterized in Drosophila, however, little is known about synchronization in non-model insect species. Therefore, we explored entrainment of locomotor activity by light and temperature in the linden bug Pyrrhocoris apterus (Heteroptera), an insect species with a strong seasonal response (reproductive diapause), which is triggered by both photoperiod and thermoperiod. Our results show that either light or temperature cycles are strong factors entraining P. apterus locomotor activity. Pyrrhocoris is able to be partially synchronized by cycles with temperature amplitude as small as 3°C and more than 50% of bugs is synchronized by 5°C steps. If conflicting zeitgebers are provided, light is the stronger signal. Linden bugs lack light-sensitive (Drosophila-like) cryptochrome. Notably, a high percentage of bugs is rhythmic even in constant light (LL) at intensity ∼400 lux, a condition which induces 100% arrhythmicity in Drosophila. However, the rhythmicity of bugs is still reduced in LL conditions, whereas rhythmicity remains unaffected in constant dark (DD). Interestingly, a similar phenomenon is observed after temperature cycles entrainment. Bugs released to constant thermophase and DD display weak rhythmicity, whereas strong rhythmicity is observed in bugs released to constant cryophase and DD. Our study describes the daily and circadian behavior of the linden bug as a response to photoperiodic and thermoperiodic entraining cues. Although the molecular mechanism of the circadian clock entrainment in the linden bug is virtually unknown, our study contributes to the knowledge of the insect circadian clock features beyond Drosophila research.
Highlights
Majority of organisms experience periodic changes in the environment, such as daily alternations of light, dark and temperature
A majority of males were strongly rhythmic in DD, the τ values were quite dispersed after temperature cycles (TCs) entrainment (Figure 1E), which resulted in a noisy average activity and the offset is visible only for the first two DD cycles
A synergistic combination of the photoperiodic and thermoperiodic entrainment (Figure 1D) synchronized locomotion with the onset during the photophase-thermophase comparable to the timing of the onset observed under light-dark cycles (LD) at 25◦C (Figure 1A)
Summary
Majority of organisms experience periodic changes in the environment, such as daily alternations of light, dark and temperature. Circadian clocks are time-measuring mechanisms that evolved as an adaptation to prepare for these external changes and to anticipate events like sun dawn, the flowering of particular plants, or avoiding predators. Circadian clocks free run under constant conditions, such as constant darkness (DD), with periodicity close to 24 h. Circadian clocks can (and need to) be synchronized with the environment. The strongest cues, the “zeitgebers” (from German Zeit: time, Geber: giver), are light-dark cycles (LD), and temperature cycles (TCs), but circadian clocks can be synchronized by other cues including food availability and social interaction (Levine et al, 2002; Dunlap et al, 2004; Sharma and Chandrashekaran, 2005; Shaw et al, 2019)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
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.
