Thermoregulation in the only nocturnal simian: the night monkey Aotus trivirgatus

Abstract

The night monkey, a tropical monkey, is the only nocturnal simian; its thermoregulation was studied for comparison with other nocturnal or diurnal primates and other tropical mammals. Resting metabolic rate was 2.6 W (closed-circuit method) and 2.8 W (open-circuit method), 24 and 18% below the value predicted from body mass. The thermoneutral zone was very narrow; the lower critical temperature (LCT) was 28 degrees C and the upper critical temperature (UCT) was 30 degrees C. The body temperature (Tb) was at its minimum (38 degrees C) at an ambient temperature (Ta) of 25 degrees C, thus below the LCT. At low Ta, the increase in metabolic rate (MR) was smaller than predicted by the Scholander model, since MR intersected to a Ta 13 degrees C above Tb when extrapolated to MR = 0; this was attributed to a decrease of body surface area by behavior. The thermal conductance at the LCT was low: 2.3 W . m-2 . degrees C-1. Above the UCT, panting was the major avenue of heat loss. The response pattern of nocturnal habits, low resting metabolic rate, low thermal conductance, and panting in the night monkey, unique among simians, is found in many other mammals of tropical and hot desert habitats; it may be considered as an alternative adaptation to the thermal environment.

Basal Metabolic Rate, Body Weight and Diet in Primates: An Evaluation of the Evidence

“…The Thermoregulatory Hypothesis The 'thermoregulatory hypothesis' sug gests that nocturnal behaviour in primates is linked to a relatively low BMR [10,[12][13][14]. This is linked to the idea that a low metabolic rate is an energy-saving adaptation found in tropical environments.…”

“…Kurland and Pearson [ 10] term this the thermoregulatory hypothe sis. A relatively low BMR in primates is often associated with nocturnal activity, a high de gree of insulation and other characteristics often associated with heat conservation [ 13,14]. Such heat-saving mechanisms are sur prising, as these species are found in tropical areas where heat conserving characteristics might not be expected to be very important.…”

“…His finding that BMR is proportional to the 0.75 power of body weight has since been confirmed by studies that include a larger number of species [2]. Although the functional reasons for this scaling relationship are unclear, it most prob ably arises out of a physiological and/or me-Recently, there has been considerable dis cussion of whether a mammal's ecology, and in particular its diet, can be used to predict its relative BMR [4][5][6][7], This has been questioned specifically for primates by Müller [8,9] Kur land and Pearson [10] and McNab and Wright [11], Another theory suggests that a low relative BMR is associated with nocturnal behaviour [12][13][14], This paper attempts to look more closely at these ideas, paying par ticular attention to the problems that might arise when inappropriate data or methods are used.…”

Relative brain size in monkeys and prosimians

“…The physiological data are comparable in that measurements are taken in a basal condition (the animal is quiet, in a postabsorptive state and in a thermoneutral temperature zone). While some of the measurements have been more carefully monitored, for example by following a 24-hr period (e.g., Muller, 1979;LeMaho et al, 1981) or tracking seasonal cycles (e.g., Perret, 1978), the overall data produce a n interspecific curve which cannot be distinguished from those of most other studies (Wieser, 1984;Heusner, 1982;Feldman and McMahon, 1983). Future physiological studies which successfully monitor and closely control for these variables are likely to lessen the variability but not change the interspecific slope.…”

Seasonal Variation of Temporal Niche in Wild Owl Monkeys (Aotus azarai azarai) of the Argentinean Chaco: A Matter of Masking?

“…A study on the thermoregulatory capacity and behavior of owl monkeys, as indicated by the resting metabolic rate at ambient temperatures ranging from 1°C to 39°C, found a rather narrow thermoneutral zone of 28-30°C in an undefined Aotus species (Le Maho et al, 1981). At lower temperatures, the monkeys started shivering thermogenesis, and with increasing cold, they adopted a spherical posture to reduce heat loss.…”