title: Thermoregulatory plasticity in free-ranging vervet monkeys, Chlorocebus pygerythrus.
abstract: We used implanted miniature data loggers to obtain the first measurements of body temperature from a free-ranging anthropoid primate. Vervet monkeys (Chlorocebus pygerythrus) living in a highly seasonal, semi-arid environment maintained a lower mean 24-h body temperature in winter (34.6 ± 0.5 °C) than in summer (36.2 ± 0.1 °C), and demonstrated increased heterothermy (as indexed by the 24-h amplitude of their body temperature rhythm) in response to proximal environmental stressors. The mean 24-h amplitude of the body temperature rhythm in summer (2.5 ± 0.1 °C) was lower than that in winter (3.2 ± 0.4 °C), with the highest amplitude for an individual monkey (5.6 °C) recorded in winter. The higher amplitude of the body temperature rhythm in winter was a consequence primarily of lower 24-h minimum body temperatures during the nocturnal phase, when monkeys were inactive. These low minimum body temperatures were associated with low black globe temperature (GLMM, β = 0.046, P < 0.001), short photoperiod (β = 0.010, P < 0.001) and low rainfall over the previous 2 months, which we used as a proxy for food availability (β = 0.001, P < 0.001). Despite the lower average winter minimum body temperatures, there was no change in the lower modal body temperature between winter and summer. Therefore, unlike the regulated physiological adjustments proposed for torpor or hibernation, these minimum winter body temperatures did not appear to reflect a regulated reduction in body temperature. The thermoregulatory plasticity nevertheless may have fitness benefits for vervet monkeys.
authors.affiliation: Brain Function Research Group, Faculty of Health Sciences, School of Physiology, University of the Witwatersrand, 7 York Road, Medical School, Parktown, Johannesburg, 2193, South Africa, alwynlubbe@gmail.com.
authors.forename: Alwyn
authors.initials: A
authors.lastname: Lubbe
authors.forename: Robyn S
authors.initials: RS
authors.lastname: Hetem
authors.forename: Richard
authors.initials: R
authors.lastname: McFarland
authors.forename: Louise
authors.initials: L
authors.lastname: Barrett
authors.forename: Peter S
authors.initials: PS
authors.lastname: Henzi
authors.forename: Duncan
authors.initials: D
authors.lastname: Mitchell
authors.forename: Leith C R
authors.initials: LC
authors.lastname: Meyer
authors.forename: Shane K
authors.initials: SK
authors.lastname: Maloney
authors.forename: Andrea
authors.initials: A
authors.lastname: Fuller
mesh_terms: D000064:Acclimatization / Q000502:physiology*; D000818:Animals; D001831:Body Temperature / Q000502:physiology; D001833:Body Temperature Regulation / Q000502:physiology*; D016663:Cercopithecinae / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D016014:Linear Models; D017440:Photoperiod; D011891:Rain; D012621:Seasons; D013019:South Africa; D018709:Statistics, Nonparametric; D013686:Telemetry