Sleep in the lesser mouse-deer (Tragulus kanchil)

• Published in: Sleep (New York, N.Y.) Vol. 45; no. 7; p. 1
• Main Authors: Lyamin, Oleg I, Siegel, Jerome M, Nazarenko, Evgeny A, Rozhnov, Viatcheslav V
• Format: Journal Article
• Language: English
• Published: US Oxford University Press 01.07.2022
• Subjects: Animals; Basic Science of Sleep and Circadian Rhythms; Ecology; Electroencephalography; Evolution; Eye movements; National parks; National parks and reserves; Predation; Sleep; Sleep disorders; Visual perception; Vietnam; Africa; Russia; sleep; slow wave sleep; ungulate; activity cycle; predation; Tragulidae; evolution; Artiodactyla; NREM sleep; environmental temperature; the lesser-mouse deer; REM sleep; Tragulus kanchil; Slow wave sleep; Sleep; Ungulate
• ISSN: 0161-8105; 1550-9109
• DOI: 10.1093/sleep/zsab199

Abstract The mouse-deer or chevrotains are the smallest of the ungulates and ruminants. They are characterized by a number of traits which are considered plesiomorphic for the Artiodactyla order. The objective of this study was to examine sleep in the lesser mouse-deer (Tragulus kanchil), which is the smallest in this group (body mass < 2.2 kg). Electroencephalogram, nuchal electromyogram, electrooculogram, and body acceleration were recorded in four adult mouse-deer females using a telemetry system in Bu Gia Map National Park in Vietnam. The mouse-deer spent on average 49.7 ± 3.0% of 24 h in non-rapid eye movement (NREM) sleep. REM sleep occupied 1.7 ± 0.3% of 24 h or 3.2 ± 0.5% of total sleep time. The average duration of REM sleep episodes was 2.0 ± 0.2 min, the average maximum was 5.1 ± 1.1 min, and the longest episodes lasted 8 min. NREM sleep occurred in sternal recumbency with the head held above the ground while 64.7 ± 6.4% of REM sleep occurred with the head resting on the ground. The eyes were open throughout most of the NREM sleep period. The mouse-deer displayed polyphasic sleep and crepuscular peaks in activity (04:00–06:00 and 18:00–19:00). The largest amounts of NREM occurred in the morning (06:00–09:00) and the smallest before dusk (at 04:00–06:00). REM sleep occurred throughout most of the daylight hours (08:00–16:00) and in the first half of the night (19:00–02:00). We suggest that the pattern and timing of sleep in the lesser mouse-deer is adapted to the survival of a small herbivorous animal, subject to predation, living in high environmental temperatures in the tropical forest undergrowth.