Changes in daily activity patterns throughout the year in a free-living South American subterranean rodent (Ctenomys coludo)

Abstract

Many species of small mammals inhabit subterranean galleries, where daily environmental cycles such as light intensity and temperature, otherwise conspicuous aboveground, are either absent or attenuated. The presence of biological rhythms was investigated in many species of these subterranean habitats. Activity patterns of the subterranean rodent tuco-tuco (Ctenomys coludo), have been studied in laboratory and semi-natural enclosures. Here we extended the description in free-living field conditions. Data from 21 tuco-tucos were collected using animal-borne accelerometers and light-loggers in 4 field campaigns across a year, covering all seasons. Accelerometer data confirmed diurnality in free-living conditions and showed that diurnality does not change throughout the year. However, a significant reduction in general activity was observed during winter. To extract more temporal information from accelerometer data, we used hidden Markov models (HMMs) classifying the data into three distinct activity states roughly corresponding to low-, medium-, and high-intensity activity. While high-intensity activities were day-concentrated and low-intensity was concentrated at night, medium-intensity activity bouts were spread throughout day and night. Furthermore, tuco-tucos displayed significant changes in the time spent in different activity states throughout the year, clarifying that the observed changes in activity levels in winter were due to reduced high activity, allocating more time to medium activities, not rest. Light-logger data confirmed the seasonal variation of daily surface emergence, concentrated in twilight hours during summer and around mid-day in winter, in contrast to general activity, which peaked around mid-day throughout the year. In addition, the HMM analysis clarified that tuco-tucos were mainly in a high-intensity activity state on the surface, which did not change throughout the year. The combination of biologgers and new analytical tools enabled more detailed characterization of activity patterns in free-living animals, expanding the scope of biological clock studies in natural conditions.