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Variability of diurnality in laboratory rodents
1Circadian Rhythm Laboratory, University of South Carolina, 807 Hampton Street, Walterboro, SC 29488, USA. refinetti@sc.edu
Summary
Rodent activity patterns vary, with some species being strictly diurnal or nocturnal, while others show mixed or graded activity. This suggests a spectrum of temporal niches rather than a simple diurnal-nocturnal divide.
Area of Science:
- Chronobiology
- Animal Behavior
- Comparative Physiology
Background:
- Understanding circadian rhythms is crucial for animal behavior research.
- Many rodent species are used in labs, exhibiting diverse activity patterns.
Purpose of the Study:
- To compare locomotor activity rhythms across seven rodent species.
- To determine if a strict diurnal-nocturnal classification applies to all species.
Main Methods:
- Monitoring running-wheel activity in a 12h:12h light:dark cycle.
- Observing activity patterns in domestic mice, lab rats, Syrian hamsters, Siberian hamsters, Mongolian gerbils, degus, and Nile grass rats.
- Using infrared motion detectors to confirm activity in nocturnal degus.
Main Results:
- Nile grass rats were diurnal; lab rats, Siberian hamsters, domestic mice, and Syrian hamsters were nocturnal.
- Mongolian gerbils and degus exhibited both diurnal and nocturnal subgroups.
- A gradient of diurnality was observed, challenging a simple diurnal-nocturnal dichotomy.
Conclusions:
- The diurnal-nocturnal classification is insufficient for some rodent species.
- Rodent temporal niches exist on a spectrum, influenced by entraining and masking processes.
- Species-specific activity patterns reflect a complex interplay of biological mechanisms, not just researcher needs.