Circadian chronotypes among wild-captured west Andean octodontids

Abstract

Rest activity pattern was studied in wild-captured males of Octodon degus (n=9), Octodon bridgesi (n=3), and Spalacopus cyanus (n=6) (Rodentia: Octodontidae). Ten-minute resolution actograms were constructed from data obtained by an automated acquisition system. After two months of habituation to a stable light-dark schedule, recordings were performed in isolation chambers under a 12: 12 Light Dark schedule. A freerunning period (constant darkness) was recorded for O. bridgesi and S. cyanus. O. degus displayed a crepuscular pattern of rest activity rhythm. Entrained O. bridgesi and S. cyanus displayed nocturnal preference, with rest anticipating light phase and without crepuscular activity bouts. Under constant darkness, active phase occurred at subjective night in O. bridgesi and S. cyanus. Wild-captured O. bridgesi and S. cyanus possess a circadian driven nocturnal preference, while wild O. degus displays a crepuscular profile. Diurnal active phase preference of wild S. cyanus colonies observed in the field could not be explained solely by photic entrainment, since social and/or masking processes appear to be operative. The genus Octodon includes species with diverse chronotypes. We propose that crepuscular diurnal pattern observed in O. degus is a recent acquisition among the octodontid lineage.