A SUBTERRANEAN RODENT?S ?NATURAL ENTRAINMENT?

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

Puebla

Congreso; Third World Congress on Chronobiology; 2011

Subterranean rodents are interesting organisms for the study of natural entrainment since they spend most of the day inside underground tunnels where there is little daily variation in environmental parameters. Due to this, it has been proposed that entrainment depends mostly on aboveground excursions, e.g., during foraging, when there might be contact with more robust cycles. Our field data on the Tuco-tuco (Ctenomys cf. knighti), indicates that these animals are exposed to the aboveground light-dark cycle through several random bouts of light-exposition in a single day. Summer measurements during 11 consecutive days revealed an average peak of exposition bouts within a 1 hour interval between 9 and 10 a.m. In order to access whether this daily light exposure pattern acts as an entraining agent, we first constructed in laboratory the Phase Response Curve (PRC) for 1h light-pulses (1000lux). The shape of the PRC, which is qualitatively similar to others reported in the literature, determines the entrainment pattern of the circadian clock to light-dark cycles. How the clock, with its PRC, responds to the irregular light-exposure pattern is being investigated by means of computer simulations. Using the software Circadiandynamix, two selected oscillator-configurations, A (type-1 PRC) and B (type-0 PRC), were submitted to potentially entraining cycles, consisting of randomly distributed light pulses confined to a fixed phase range of the day. Several simulations were performed by changing this phase range from 2 to 12 hours. Unexpectedly, oscillator A maintained a relative stable entrainment even under the most irregular (12-hours phase range) cycle. Oscillator B, in turn, presented a pattern resembling relative coordination under this same regimen. Simulation results are consistent with a nocturnal animal exposed to light during its rest phase, and this seems paradoxal, especially for subterranean nocturnal animals that rest inside dark underground tunnels. However, field-lab experiments indicate that, in spite of its nocturnal-phased oscillator, Tuco-tucos indeed express diurnal aboveground activity in the field.