1Anatomy & Neurobiology, Northeast Ohio Medical University, 2Biomedical Sciences, Ohio University, 3Evolutionary Anthropology, Duke University, 4Department of Physical Therapy, High Point University
Saturday 4:30-4:45, 200ABC
Free-ranging mammals are confronted with the challenge of maintaining an energetically neutral body temperature within a thermally dynamic environment that changes daily, seasonally, and annually. While many laboratory studies have been conducted on primate thermoregulation, we know comparatively little about the thermal pressures primates face in their natural, evolutionarily-relevant environment. We examined thermoregulation of free-ranging mantled howling monkeys in a lowland tropical dry forest in Guanacaste province, Costa Rica. We recorded subcutaneous (Tsc) and near-animal ambient temperature (Ta) from 11 animals at 10 min intervals over 1606 sample hours. We found significant positive daily cross-correlations between Ta and Tsc (average r=0.70±0.17) with a modal (44% of days) lag time <10 min. Tsc increased with higher Ta, but plateaued at Ta >41°C. Similarly, 95% of dry season cases with Ta>Tsc occurred at Ta>38.1°C, which implies that howlers use a cooling response to prevent rising temperatures over a threshold Ta. However, this cooling response was relatively infrequent, with Tsc being below Ta in only 14% of dry and <1% of wet season samples. The magnitude of cool vs. warm stress differed as well, showing a maximum deviation of 4.8°C when Ta>Tsc, vs. 15.4°C when Ta<Tsc. Our data support a hypothesis that, despite inhabiting a dry tropical environment, howling monkeys experience more ‘cool’ than ‘heat’ stress. This suggests that cool temperatures may be a prevalent thermoregulatory challenge for primates, particularly smaller primates living at higher latitudes and/or altitudes.
NSF, Ohio University Baker Award, Duke University A&S Council