Annual variation in an ultradian component in the locomotor activity rhythm of the common marmoset (Callithrix jacchus)

Daily locomotor activity in common marmosets shows a decrease near the middle of the active phase, as observed for captive and wild living animals. An important 8 h period component detected in spectral analysis shows annual variation. To determine the environmental factors that are correlated with this finding, three animals were observed during infant and juvenile stages in outdoor cages under natural temperature, humidity and light cycles. Data were collected from sunrise to sunset, three consecutive days a week, at 5 min intervals randomly distributed inside the clock hours, and were recorded as the total of arbitrary cage sections traveled by the animal each interval. From the Fourier analysis of weekly data series we calculated the relative power of the 8 h period component. Pearson's correlation rest showed that the relative power correlates better with environmental temperature and photophase duration than with relative humidity or rainfall. Amplitude but not acrophase showed significant differences (Kruskall-Wallis test, p<0.01) between seasons. These findings suggest that the annual variation in the 8 h period component could result from a temperature modulation on the locomotor activity rhythm.