Ectothermic organisms often experience considerable variation in their body temperature throughout the circadian cycle. However, studies focusing on the measurement of physiological traits are usually performed under constant temperature regimes. This mismatch between thermal exposure in the field and experimental conditions could act as a stressor agent, since physiological functions are strongly influenced by temperature. Herein, we asked the question whether constant thermal regimes would cause a stress response and impact the immunity of the South American rattlesnake (Crotalus durissus) when compared to a fluctuating thermal regime. We addressed this question by determining heterophil:lymphocyte ratio (H:L), plasma bacteria killing ability (BKA) and corticosterone levels (CORT) in snakes kept under a constant temperature regime at 30°C, and under a fluctuating regime that oscillated between 25°C at nighttime to 35°C at daytime. The experiments had a mirrored design, in which half of the snakes were subjected to a fluctuating-to-constant treatment, while the other half was exposed to a constant-to-fluctuating treatment. The shift from constant to fluctuating thermal regime was accompanied by an increase in plasma CORT levels indicating the activation of a stress response. Exposure to a fluctuating thermal regime at the onset of the experiments induced a decrease in the BKA of rattlesnakes. H:L was not affected by treatments and, therefore, the shift between thermal regimes seems to have acted as a low intensity stressor. Our results suggest that the removal from temperatures close to the snakés preferred body temperature triggers a stress response in rattlesnakes.

Tropical forests are key habitats for diverse organisms, and because of their wide global distribution, rich biodiversity, and long history of human use, they are also essential for providing a wide range of ecosystem services (ESs;Brandon, 2015; Brockerhoff et al., 2017;Gibson et al., 2011;Mori et al., 2017). Considerable attention has been devoted to tropical forests and their role as a natural climate solution for mitigating climate change. It is estimated that about 30% of all CO 2 emitted by human activities is removed from the atmosphere by these forests (Le Quéré et al., 2018). The important role of tropical forests as a carbon sink and stock has historically guided conservation pacts, programs, and policies for establishing targets associated with carbon storage and climate change mitigation. This role was important in developing several articles of the 1997 Kyoto Protocol (Swingland et al., 2002) and explicit policies for reducing emissions from deforestation and forest degradation through the REDD+ agreement (Pistorius, 2012). Several countries also set ambitious goals for restoring forests to reduce emissions or sequester carbon in the United Nations Framework Convention on Climate Change 2015 Paris Agreement. The land use, land cover change, and forestry (LULCCF) sector is included in many countries' first nationally determined contributions (NDCs) but with differing levels of specificity. Assuming full implementation of NDCs, Grassi et al. (2017) show that land use-and forests, in particular-emerges as a key component of the Paris Agreement: global land use will turn from a net anthropogenic source during 1990-2010 (1.3 ± 1.1 Gt CO 2 e yr −1 ) to a net sink of carbon by 2030 (up to −1.1 ± 0.5 Gt CO 2 e yr −1 ) and would provide a quarter of countries' planned emission reductions. Two tropical countries stand out regarding the magnitude of the LULCCF contribution: Brazil set ambitious goals of reducing greenhouse gas emissions by 43% by 2030 with

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