SAUVÉ-ROZON_MSc_R_Data

Seasonal rhythms are widely documented in wild organisms across diverse species. Seasonality in laboratory rodents, however, remains an intriguing phenomenon, considering that laboratory conditions are supposed to be constant throughout the year. Here, I study seasonality in locomotor activity and body mass measurements taken as part of a long-term artificial selection experiment involving ~36,002 house mice (Hsd:ICR) spanning 78 generations across 23 years. This dataset includes four replicate lines selectively bred for high voluntary wheel-running behaviour and four non-selected control lines. In the experiment, approximately four generations per year occurred. Continuous wavelet transforms (CWT) revealed strong circannual rhythmicity with inverted 12-month cycles in both wheel-running distance and body mass, although amplitude declined in the last 5 years across all 8 lines. I applied generalized additive mixed models (GAMMs) to test group differences between sex, line type, and laboratory location (University of Wisconsin–Madison, where the experiment started and ran through 31 generations, versus University of California, Riverside) in running distance, duration, speed (both of which are components of running distance), and body mass (measured before and after 6 days of wheel running). Running distance showed greater amplitude in selected than control lines and in males than females. Running duration and body mass cycles were stronger in Wisconsin than Riverside, again with males showing higher amplitudes than females. For running speed, selected lines had more seasonality than control lines. These results unambiguously demonstrate persistent seasonal cycles in behaviour and morphology under controlled laboratory conditions, without, however, being able to distinguish between endogenous circannual mechanisms maintained across generations or subtle environmental cues within housing facilities as a definitive explanation for this phenomenon. This thesis contributes to the understanding of seasonal cycles and stresses the importance of considering them to improve reproducibility and reliability of research using laboratory mice.