Multiple factors can influence the immune response of vertebrate ectotherms, including body temperature, gonadal steroids, and seasonality, in ways that are thought to reflect trade-offs between energetic investment in immunity vs. reproduction. Hibernating tegu lizards (Salvator merianae) are a unique model to investigate how immunocompetence might be influenced by different factors during their annual cycle. We assessed immunological measures (plasma bacterial killing ability (BKA), total and differential leukocyte count), plasma hormone levels (testosterone in males, estradiol and progesterone in females, and corticosterone in both sexes), body temperature, and body condition from adult tegus during each stage of their annual cycle: reproduction, post-reproduction/preparation for hibernation, and hibernation during the years of 2017 and 2018. The animals sampled in this study were captive-bred of both sexes (10 males and 11 females) kept in a communal outdoor enclosure (42 m²) subject to natural fluctuations in temperature, daylight, humidity, and rainfall, at the campus of Universidade Estadual Paulista (UNESP) in Jaboticabal, São Paulo, Brazil (21°14′05″S and 48°17′09″W). We measured body mass to the nearest ±1 g on a digital scale, snout-vent length and tail thickness using a meter scale (± 0.01 cm). Blood was collected from the ventral coccygeal vein using a heparinized 5 mL syringe and a 21 G needle. Total handling time was ∼ 3 min to minimize potential effects of handling stress. Blood samples were used for total and differential leukocyte count, quantification of steroid plasma levels, and BKA. Body temperature was obtained from temperature loggers that were surgically implanted in each animal's coelomatic cavity and sutured to the internal muscle layer, each logger was programmed to measure and record Tb every 70 min.Hormonal data and body temperature data is published in Zena et al. 2019 and 2020.

For the differential lykocyte component, blood smears were prepared and 100 leukocytes (eosinophils, monocytes, basophils, heterophils, and lymphocytes) counted. A Varimax normalized principal component analysis (PCA) was carried out on the number of basophils, eosinophils, monocytes and azurophils sampled in each month compiled, but separately for males and females. From the obtained component, a compound residual was extracted by regression and recorded as differential leukocyte component.The body condition index and tail fat index were calculated by extracting the residuals of a standard least squares linear regression using snout-vent length as the independent variable and body mass or tail thickness, respectively, as the dependent variable.Plasma bacterial ability was assayed against Escherichia coli.#999: not analysed