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Gen Comp Endocrinol
2023 Aug 01;339:114291. doi: 10.1016/j.ygcen.2023.114291.
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Baseline corticosterone levels in spadefoot toads reflect alternate larval diets one year later.
Ledón-Rettig CC
,
Lo KM
,
Lagon SR
.
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Early-life environmental variation can influence later-life physiology, such as the regulation of glucocorticoids. However, characterizing the effects of environmental factors on hormone regulation can be hampered when assessing animals that are small and require destructive sampling to collect blood. Using spadefoot toads (genus Spea), we evaluated whether waterborne corticosterone (CORT) measures could be used as a proxy for plasma CORT measures, detect stress-induced levels of CORT, and detect larval diet-induced changes in CORT regulation after metamorphosed individuals were maintained for 1 year under common garden conditions. We found that waterborne CORT measures were correlated with plasma CORT measures and could be used to detect stress-induced levels of CORT. Further, larval diet type significantly influenced baseline plasma CORT levels 1-year post-metamorphosis: adults that had consumed live prey as larvae had higher plasma CORT levels than adults that had consumed detritus as larvae. However, waterborne measures failed to reflect these differences, possibly due to low sample size. Our study demonstrates the utility of the waterborne hormone assay in assessing variation in baseline and stress-induced CORT levels in adult spadefoots. However, resolving more subtle differences that arise through developmental plasticity will require larger samples sizes when using the waterborne assay.
Fig. 1. Experimental Design. (A) Tadpoles were raised on a shrimp or detritus diet from hatching until metamorphosis, and then under common garden conditions for 1 y. (B) Waterborne samples – represented by the grey drops – were collected at 2 time points. This procedure was repeated for each individual after 5 d of rest (i.e., there were 2 trials). Additionally, we collected a blood sample – represented by the black drop – after the 2nd trial
Fig. 2. Baseline waterborne CORT measures are positively and significantly correlated with baseline plasma CORT measures. R2partial reflects the strength of the relationship between plasma and waterborne CORT measures after the effect of trial is removed. A 95% confidence interval for predictions from a linear model is displayed around the regression.
Fig. 3. Larval diet significantly impacts adult plasma CORT measures 1 y after growth in common garden conditions. The lines that intersect boxes represent median values, limits of the boxes represent the interquartile range of the data (25th and 75th percentiles), and whiskers represent the maximum values of the data under and over the 25th and 75th percentiles, respectively. Adult weight at the time plasma CORT was measured was included as a covariate in the model.
Fig. 4. Waterborne samples detect stress-induced CORT. Across trials, waterborne CORT levels were significantly higher 1 h after adults experienced a stressor (asterisk denotes p = 0.001); size-adjusted CORT (pg/mL/g) is shown for visualization. Neither trial nor larval diet significantly influenced waterborne CORT measures. The lines that intersect boxes represent median values, limits of the boxes represent the interquartile range of the data (25th and 75th percentiles), and whiskers represent the maximum values of the data 1.5 times the interquartile range under and over the 25th and 75th percentiles, respectively. Points indicate outliers beyond the interquartile range.
