Thompson Cynthia L, Powell Brianna L, Williams Susan H, Hanya Goro, Glander Kenneth E, Vinyard Christopher J
Department of Biomedical Sciences, Grand Valley State University, Allendale, Michigan.
Department of Biology, Grand Valley State University, Allendale, Michigan.
Am J Primatol. 2017 Nov;79(11). doi: 10.1002/ajp.22714. Epub 2017 Oct 19.
Thyroid hormones boost animals' basal metabolic rate and represent an important thermoregulatory pathway for mammals that face cold temperatures. Whereas the cold thermal pressures experienced by primates in seasonal habitats at high latitudes and elevations are often apparent, tropical habitats also display distinct wet and dry seasons with modest changes in thermal environment. We assessed seasonal and temperature-related changes in thyroid hormone levels for two primate species in disparate thermal environments, tropical mantled howlers (Alouatta palliata), and seasonally cold-habitat Japanese macaques (Macaca fuscata). We collected urine and feces from animals and used ELISA to quantify levels of the thyroid hormone triiodothyronine (fT ). For both species, fT levels were significantly higher during the cooler season (wet/winter), consistent with a thermoregulatory role. Likewise, both species displayed greater temperature deficits (i.e., the degree to which animals warm their body temperature relative to ambient) during the cooler season, indicating greater thermoregulatory pressures during this time. Independently of season, Japanese macaques displayed increasing fT levels with decreasing recently experienced maximum temperatures, but no relationship between fT and recently experienced minimum temperatures. Howlers increased fT levels as recently experienced minimum temperatures decreased, although demonstrated the opposite relationship with maximum temperatures. This may reflect natural thermal variation in howlers' habitat: wet seasons had cooler minimum and mean temperatures than the dry season, but similar maximum temperatures. Overall, our findings support the hypothesis that both tropical howlers and seasonally cold-habitat Japanese macaques utilize thyroid hormones as a mechanism to boost metabolism in response to thermoregulatory pressures. This implies that cool thermal pressures faced by tropical primates are sufficient to invoke an energetically costly and relatively longer-term thermoregulatory pathway. The well-established relationship between thyroid hormones and energetics suggests that the seasonal hormonal changes we observed could influence many commonly studied behaviors including food choice, range use, and activity patterns.
甲状腺激素可提高动物的基础代谢率，对于面临低温的哺乳动物而言，它是一条重要的体温调节途径。尽管高纬度和高海拔地区季节性栖息地的灵长类动物所经历的寒冷热压力往往很明显，但热带栖息地也有明显的干湿季节，热环境会有适度变化。我们评估了两种处于不同热环境中的灵长类动物——热带鬃毛吼猴（Alouatta palliata）和季节性寒冷栖息地的日本猕猴（Macaca fuscata）——甲状腺激素水平的季节性变化和与温度相关的变化。我们收集了动物的尿液和粪便，并使用酶联免疫吸附测定法（ELISA）来量化甲状腺激素三碘甲状腺原氨酸（fT）的水平。对于这两个物种，fT水平在较凉爽的季节（湿季/冬季）显著更高，这与体温调节作用一致。同样，这两个物种在较凉爽的季节都表现出更大的温度赤字（即动物将体温相对于环境温度升高的程度），表明在此期间体温调节压力更大。与季节无关，日本猕猴的fT水平随着近期经历的最高温度降低而升高，但fT与近期经历的最低温度之间没有关系。吼猴随着近期经历的最低温度降低而fT水平升高，尽管与最高温度呈现相反的关系。这可能反映了吼猴栖息地的自然热变化：湿季的最低温度和平均温度比干季更凉爽，但最高温度相似。总体而言，我们的研究结果支持以下假设：热带吼猴和季节性寒冷栖息地的日本猕猴都利用甲状腺激素作为一种机制，以应对体温调节压力来提高新陈代谢。这意味着热带灵长类动物面临的凉爽热压力足以引发一种能量消耗大且相对长期的体温调节途径。甲状腺激素与能量学之间已确立的关系表明，我们观察到的季节性激素变化可能会影响许多常见的研究行为，包括食物选择、活动范围利用和活动模式。
