Seasonal Variation in Corticosterone in Free-Living and Captive Eastern Red-spotted Newts Notophthalmus viridescens viridescens
Hypothalamic–pituitary–adrenal (HPA, or HPI —interrenal in amphibians) function and the typical stress response system can be altered in many ways. Glucocorticoids (GC) are modulated seasonally in a variety of vertebrate taxa, and long-term captivity also modifies the HPA/I axis. Our experiment investigated the functioning of the HPI axis in free-living and long-term captive Eastern Red-spotted Newts. Free-living newts were collected and blood sampled throughout and after the breeding season in 2006–2007, and 2010. Captive newts arrived in the laboratory in December 2006 and their blood was also sampled in pre-, late-, and postbreeding season in 2007. Contrary to most other amphibians exhibiting seasonality in plasma corticosterone (CORT, the predominant GC in amphibians) levels, the peak in CORT in free-living newts was not related to the breeding season. As expected, captive newts had higher baseline levels of plasma CORT than free-living newts. However, whereas stress-induced CORT levels were equivalent in free-living and captive newts in July (postbreeding), stress-induced concentrations were significantly lower in free-living newts in both January (prebreeding) and April (late breeding). These data suggest that HPI function is altered by captivity in newts.Abstract
Mean ± SEM plasma corticosterone (CORT) (ng/ml) in Eastern Red-spotted Newts sampled in the field. Open circles are 3-min plasma CORT and filled squares are 30-min plasma CORT. CORT was undetectable in February, March, and October at 3 min. Some error bars were too small to show up. Letters indicate homogeneous groups across time of year at 3 (P = 0.019) or 30 (P < 0.0001) min (Duncan-Waller test). Symbols a and b reflect significant differences in 3-min CORT values, and x, y, and z reflect significant differences among 30-min CORT values. Asterisks indicate significantly higher mean CORT at 30 min compared to 3 min for the same month as determined by Student's t-test (P < 0.05). Beginning with January, for 3-min data n = 10, 6, 12, 11, 10, 5, 10, and 12; for 30-min data n = 9, 6, 12, 10, 12, 6, 10, and 10.
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