Establishing Tribolium castaneum as a new model for studying individual variation and evolution of circadian rhythms

• Applicants: Professor Dr. Joachim Kurtz; Professor Dr. Ralf Stanewsky
• Subject Area: Evolution, Anthropology ; Sensory and Behavioural Biology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 551960251

Circadian clocks are ubiquitous and maximize the fitness of organisms by allowing them to synchronize with the 24-hour changes in their environment caused by the Earth's rotation, and to anticipate rather than simply react to these changes. While the general mechanisms of these pacemakers are evolutionarily highly conserved, the variation in the molecular composition of circadian clocks between species demonstrates remarkable evolutionary flexibility, allowing adaptations to species-specific ecological demands. Nevertheless, research on the individual variation of circadian rhythms within species and its significance for the evolution of circadian clocks remains limited. In this context, we propose to use the red flour beetle, Tribolium castaneum, as a new model for investigating circadian clock evolution, with a focus on within-species diversity as the basis for evolutionary adaptation. In contrast to most model organisms employed in chronobiological studies, this beetle exhibits considerable individual variation in rhythmicity. Some individuals display clear rhythmic behaviour, while others are arrhythmic. The proposed research aims to utilise this natural variation in behaviour, in combination with the intrinsic strengths of this model, such as large-scale breeding capacity and well-established genetic and genomic tools, to address key questions regarding the evolvability of rhythmic behaviour. Our overarching hypothesis is that individual variation in rhythmic behaviour in T. castaneum is a relevant biological phenomenon with genetic underpinnings, subject to selection pressures. Additionally, the study aims to elucidate the role of social interactions in synchronizing circadian rhythms within groups of group-living insects, potentially masking individual variations and enhancing overall circadian rhythmicity. Therefore, we will establish valuable tools such as clock gene mutations as well as beetle lines with stable expression of a clock-luciferase enhancer trap and fusion gene to analyse the molecular mechanisms of the T.castaneum clock. Furthermore, we propose to perform selection lines to prove evolvability of the seen behavioural variation. To investigate the origin of this behavioural evolution, we will analyse rhythmic transcription by RNAseq of selection line samples. Finally, we will determine the influence of social cues on both molecular and behavioural circadian rhythms. We will use video tracking and bioluminescence measurements of the luciferase beetle lines to determine whether the behavioural variability observed in individual beetles, is reflected by the beetles’ circadian clocks and can be reduced by social interactions.

• DFG Programme: Research Grants