AFTEREFFECTS OF ENTRAINMENT IN THE FIELD PROVIDE NEW INSIGHTS OF THE SWITCH FROM DIURNALITY TO NOCTURNALITY IN THE SUBTERRANEAN RODENT TUCO-TUCO (Ctenomys cf. knighti),

- TOMOTANI BM; FLÔRES DEFL; TACHINARDI P; PALIZA J D; ODA GA; VALENTINUZZI VS

Puebla

Congreso; Third World Congress on Chronobiology; 2011

Ctenomys cf. knighti, a subterranean rodent from Anillaco (La Rioja, Argentina), is clearly nocturnal when kept under LD 12:12 (L: 200 lux) in cages with running-wheels in laboratory. However, when we continuously observed two individuals in a seminatural enclosure (10 x 5 meters) during the day (one during winter for 12 hours, one during summer for 14 hours), they surprisingly emerged aboveground throughout the day, showing diurnal activity outside the burrow. This indicated that C. cf. knighti could be another species that switches from diurnality to nocturnality when transferred from the field to the laboratory, as has been reported in some other wild diurnal rodent species. We needed to verify whether the observed diurnal aboveground activity is a component of their total daily activity that is diurnal (above and underground) or if this animal is not entrained in the field and thus the observed aboveground activity is just part of randomly timed activity bouts during the day.  In order to approach this question, and based on the fact that circadian oscillators often display aftereffects of entrainment, we transferred the observed animals after the end of observations from the enclosures to the laboratory under constant conditions. This way, we could register the aftereffects of the previous field synchronization and access the phase of the synchronized oscillator in the field. The result was surprising: the activity phase of both animals coincided with the external night. In order to verify the generality of these results, we brought 11 more animals now directly from the field to the laboratory under constant conditions: five in running wheels and six with infrared motion sensors.  Independently of the measuring device, activity phase was that of a nocturnal animal. We conclude that the activity phase of tuco-tuco is nocturnal, as dictated by the LD entrained oscillator but its expression is diurnal only in the field, due to masking by some environmental cycle other than the light-dark. Some hypothesis about the masking factors are temperature and oxygen content cycles in the underground environment.