Abstract:
Many animals adapt their activity patterns to the best environmental
conditions using daily rhythms. African mole-rats are among the mammals
that have become models for studying how these rhythms can be entrained
by light or temperature in experimental laboratory studies. However, it
is unclear whether they exhibit similar circadian rhythms in their natural
lightless, subterranean environment. In this study, we used biologging to
investigate the activity rhythms of wild, highveld mole-rats. We show that
their activity cycle exhibited an ultradian rhythm with a length between
4 and 8 h. On an individual level, mole-rats displayed about five activity
bouts per day, occurring at various times during the day and night. On
a population level, activity peaked in the afternoon, coinciding with the
peak in ambient temperature. Our research suggests that wild subterranean
mammals, which experience reduced environmental variation, are unlikely
to show clear circadian rhythmicity in activity patterns. Instead, activity
periods are distributed over several bouts throughout the day and night,
and activity coincides with the peak in daily temperature. We propose
that ultradian rhythms in activity may be more common than previously
thought and discuss how physiological processes may generate differences
in periodicity between laboratory and wild populations.
