Telling the seasons underground: light exposure and photoperiodism in a subterranean rodent

ODA GA; FLÔRES DELF; JANNETTI MG; IMPROTA GC; TACHINARDI P; SILVA JS; VALENTINUZZI VS

Hawái

Simposio; International Bio-Logging Science Symposium; 2021

The ability to track photoperiod, the proportion of light and darkness hours within a day, is used by organisms to anticipate the seasons and time their seasonal physiology. We investigated the limits of photoperiod measurement in a South American subterranean rodent, the tuco-tuco (Ctenomys aff. knighti) combining field work, laboratory experiments and mathematical modeling. Photoperiod measurement has been traditionally studied in lab experiments, under artificially imposed light/dark cycles. In contrast, tuco-tucos´ exposure to light is sporadic and results from their own behavior of emergence to the surface. Thus, we hypothesized that if photoperiod is playing a role in the synchronization of their annual program, they should expose to different daylengths throughout the year by seasonally modifying the timing of their surface emergences. Tuco-tucos were released into 3 individual semi-natural enclosures (12 X 6 X 1.5m and 1m deep) carrying light-loggers (W65, 0.65g, Migrate Technology, UK) and accelerometers (Axy-3, 2g, Techno Smart, Italy) during summer and winter months spanning 3 years. A total of 22 tuco-tucos were successfully recaptured after different deployment durations (15 to 150 days). Surface and soil temperatures (20cm) were continuously measured. Accelerometers tracked daily activity rhythms of these small rodents (188±27g) in their natural habitat, while light-loggers indicated time on surface and consequent light-exposure. These data confirmed seasonal variation in the daily timing of surface emergence, which was partly shaped by a combination of surface and soil temperatures. The endogenous regulation of this seasonal activity by the circadian clock was indicated by lab constant lighting experiments. Finally, a multi-oscillator circadian clock was computer simulated under light regimens that mimicked tuco-tuco?s light exposure across the seasons, showing its sufficiency for photoperiod encoding. Together, our results elucidate minimal light/dark patterns that convey photoperiod information in this extreme photic environment, contributing to the knowledge built from traditional laboratory experiments.