Madelaire CB and Gomes FR (2023), Relationships between hormone levels, metabolis...

XB-ART-59962

Gen Comp Endocrinol 2023 Jul 01;338:114263. doi: 10.1016/j.ygcen.2023.114263.

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Relationships between hormone levels, metabolism and immune response in toads from a semi-arid region.

Madelaire CB , Gomes FR .

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Steroid hormones (e.g. androgens [AN] and corticosterone [CORT]) modulate complex physiological functions such as reproduction, energy mobilization, metabolism, and immunity. The effects of these steroids on immunocompetence and its metabolic costs can also be affected by fluctuations in environmental resource availability and other factors such as parasitism. To understand these possible interactions, we studied AN and CORT, immune response [swelling response to phytohemagglutinin (PHA) injection and bacterial killing ability (BKA)], parasite load, resting metabolic rate (RMR) and post-immune challenge (PHA injection) oxygen consumption rates during two different phases of the annual cycle of Rhinella jimi toads from the Brazilian semi-arid region (Caatinga), where environmental conditions are highly seasonal. We observed an increase in O2 consumption rates after both PHA and saline (control) injections, indicating a metabolic response to adverse stimuli rather than the immune challenge. Toads showing higher RMR and VO2 after the adverse stimuli (PHA/saline injections) had lower field AN and CORT plasma levels, suggesting these hormones might mediate a metabolic energy conservation strategy both at baseline levels and after adverse stimuli. Parasite load appear to constrain the metabolic response to PHA and saline injections. Additionally, individuals with a higher swelling response to PHA had higher field CORT plasma levels (particularly when males are breeding), which opposes the idea of a possible trade-off between reproductive activity and other physiological traits, indicating the immunoenhancing effects of elevated CORT at physiological levels. BKA did not show a seasonal variation or correlation with body condition or hormone levels, indicating that the immune surveillance mediated by the complement remains constant despite ecological and physiological changes.

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	Fig. 1. Experimental procedure for Rhinella jimi males collected during rainy and dry season, and breeding event. After a day in captivity, animals collected during rainy (n = 25) and dry period (n = 8) had their resting metabolic rate measured for 24 h, followed by an injection of either PHA or saline. The metabolic rate in response to PHA or saline injection was measured for 50–55 h. For breeding animals (calling males, n = 5) collected during the rainy season, PHA response was measured without performing any metabolic measurements. Blood samples collected in the field for all animals (n = 38) were used for measuring field hormone plasma levels [androgens (AN) and corticosterone], and plasma bacterial killing ability (BKA). Endoparasites were collected and counted after euthanasia (n = 38), and body index was calculated using body mass and snout-vent length (n = 38).
	Fig. 2. Rhinella jimi oxygen consumption and metabolic cost after PHA and saline injections across rainy and dry season. (A) Baseline oxygen consumption (RMR, n = 26), and after injecting animals with either PHA (n = 18) or saline (n = 13) injection, across rainy and dry season. (B) Metabolic cost (VO2 after injection minus RMR) in response to PHA (n = 14) and saline (n = 12), during rainy and dry season. Data are median with interquartile range. In (A) different letters indicate significant differences within seasons (Wilcoxon or t-test: P < 0.05).
	Fig. 2. Rhinella jimi oxygen consumption and metabolic cost after PHA and saline injections across rainy and dry season. (A) Baseline oxygen consumption (RMR, n = 26), and after injecting animals with either PHA (n = 18) or saline (n = 13) injection, across rainy and dry season. (B) Metabolic cost (VO2 after injection minus RMR) in response to PHA (n = 14) and saline (n = 12), during rainy and dry season. Data are median with interquartile range. In (A) different letters indicate significant differences within seasons (Wilcoxon or t-test: P < 0.05).
	Fig. 3. Relation between resting metabolic rate in the lab and field hormone plasma levels of Rhinella jimi. Scatterplot of resting metabolic rate versus field plasma levels of (A) androgens (n = 24), and (B) corticosterone (n = 24). Line shown indicates best fit.
	Fig. 3. Relation between resting metabolic rate in the lab and field hormone plasma levels of Rhinella jimi. Scatterplot of resting metabolic rate versus field plasma levels of (A) androgens (n = 24), and (B) corticosterone (n = 24). Line shown indicates best fit.
	Fig. 4. Relation between metabolic cost of PHA and saline injections, parasite load and field androgens plasma levels of Rhinella jimi. Scatterplot of (A) metabolic cost (VO2 after injection minus RMR) in response to PHA and saline, parasite load and field androgens plasma levels (n = 24), and (B) parasite load and field androgens plasma levels of Rhinella jimi (n = 28). Line shown in B indicates best fit.
	Fig. 4. Relation between metabolic cost of PHA and saline injections, parasite load and field androgens plasma levels of Rhinella jimi. Scatterplot of (A) metabolic cost (VO2 after injection minus RMR) in response to PHA and saline, parasite load and field androgens plasma levels (n = 24), and (B) parasite load and field androgens plasma levels of Rhinella jimi (n = 28). Line shown in B indicates best fit.
	Fig. 5. Relation between metabolic cost and field corticosterone plasma levels of Rhinella jimi. Scatterplot of metabolic cost (VO2 after injection minus RMR) in response to PHA and saline, and field corticosterone plasma levels during rainy (n = 17) and dry season (n = 8). Line shown indicates best fit for each season.
	Fig. 6. Relation between immune variables, field hormone levels plasma levels and body condition of Rhinella jimi. Scatterplots of swelling response to PHA injection, and (A) field androgens plasma levels (n = 17), (B) field corticosterone plasma levels (n = 16) during rainy, dry season, and breeding event; and (C) body condition (n = 17). Scatterplots of plasma bacterial killing ability, and (D) field androgens plasma levels (n = 35), (E) field corticosterone plasma levels (n = 34); and (F) body condition (n = 36) during rainy, dry season and breeding event. Line shown indicates best fit.
	Supplementary Fig. S1. Correlation between androgens and corticosterone plasma levels of Rhinella jimi. Graph axes are log 2 transformed to better data visualization. Pearson r = 0.29; P = 0.04, R2 = 0.09.
	Supplementary Fig. S2. Relationships between oxygen consumption of Rhinella jimi and air temperature. Scatterplot of air temperature registered at the moment of measuring (A) resting metabolic rate (n = 26) and (B) oxygen consumption after PHA/saline injection (n = 31).