Nocturnal to diurnal switches of tuco-tucos (Ctenomys coludo) in semi-natural burrow systems inside the laboratory

Although many species are classified as strictly diurnal or nocturnal, the temporal distribution of daily activity can be flexible for several species. The subterranean rodent tuco-tuco ( Ctenomys coludo) presents this flexibility, switching from diurnality to nocturnality when transferred from field to laboratory. Semi-natural environments (between field and lab) provide insights due to the partial maintenance of elements of both environments. In a sequence of previous studies, we have gradually explored distinct semi-natural conditions and our main goal here was to test if the nocturnal-to-diurnal switch could be reproduced in a controlled, minimalistic “mini-field” constructed inside the lab. These were glass boxes (50 × 50 × 90 cm) half-filled with soil where subterranean tuco-tucos could dig and establish galleries, as they do in nature, while environmental variables, such as temperature and food availability were controlled. Animals wore accelerometers and light-loggers to record activity and light exposure patterns, while video recordings monitored behaviors on the surface. 11 of 16 tuco-tucos switched abruptly to diurnal patterns upon transfer from cages to terrariums, with the phase of activity onsets and offsets switching to offset and onsets, respectively. Accelerometry data were subjected to behavioral classification analysis using a machine learning model prediction (HMM Hidden Markov Models) previously trained with tuco-tucos in standard cages. Because terrariums allowed subterranean tuco-tucos to express field behaviors refrained in cages, our video analysis provided additional validation to the HMM model. This analysis confirmed that the most rhythmic and the defining element of diurnal or nocturnal pattern in tuco-tucos are the high intensity activities and showed that these are behaviors such as digging and soil removal performed on the surface.