Effects of corticosterone and ACTH on the unken reflex in rough-skinned newts (Taricha granulosa) Sydney Greenfield, Lori Neuman-Lee, and Dr. Susannah French Department of Biology, Utah State University

INTRODUCTION DISCUSSION

•Stressful events such as a predator •Overall, this study provides evidence attacks stimulate a multitude of that CORT is involved in mediating anti- physiological events, including the predator behavior in newts. The interplay activation of the hypothalamic-pituitary- between ACTH, glucocorticoids, and adrenal (HPA) axis. The consequential anti-predator behavior is poorly release of glucocorticoids, such as understood and like many other corticosterone (CORT), from the adrenal hormone-physiological response glands stimulates the mobilization of relationships, is complex. energy stores for anti-predator behavior. •Animals given CORT and those given •One such important anti-predator ACTH spent on average less time in behavior for rough-skinned newts unken than those that were given the (Taricha granulosa) is the unken reflex. control or the CORT blocker. As expected, those given saline or CORT When threatened, rough-skinned newts Photos courtesy of Andrew Durso and Tyler Hansen curl up to expose a brightly colored blocker had much lower levels of ventral side (Image 1 and 2). The circulating CORT when compared to Image 1. and 2. The unken reflex of the rough-skinned newt (Taricha granulosa) exposed aposematic coloration warns those given ACTH or CORT. However, potential predators of the newts’ toxicity. those given ACTH or CORT also spent Rough-skinned newts release less time in unken. Together, these trends tetrodotoxin (TTX), the same lethal toxin suggest CORT could be inhibiting utilized by many pufferfish and the blue- unken, although further tests would be ringed octopus [1]. Results needed to confirm this finding. •We found the time in unken was correlated to CORT levels for newts given •Previous pilot studies found a strong CORT injections. •Potentially, rough-skinned newts could correlation between time in unken and benefit from limiting time in unken •However, those given ACTH, metyrapone, and saline had unken times that were should their warnings fail to stop increased levels of CORT Additionally, not significantly correlated to CORT levels in the blood. previous studies on tree lizards found potential predators. For although some that elevated CORT in the blood •While there was a large amount of individual variation, CORT and ACTH- newts have been found to produce lethal enhanced anti-predator behaviors in male injected newts had elevated levels of CORT, but suppressed time in unken. levels of TTX, certain populations of tree lizards [2]. Garter Snake (Thamnophis sirtalis) have developed a resistance to TTX and •This study sought to uncover the role of regularly consume the toxic newts [3]. If CORT and the hormone that stimulates 2000.00 a newt was confronted by a TTX resistant or naïve predator it would be CORT, adrenocorticotropic hormone 1800.00 (ACTH), in the unken reflex of rough- beneficial for the newt to abandon unken skinned newts. 1600.00 and attempt a different anti-predator defense, such as escape. Control 1400.00

Cort 1200.00

ACTH 1000.00 Metyrapone 800.00 REFERENCES [1] Miyazawa, K. and T. Noguchi (2001). 600.00 "DISTRIBUTION AND ORIGIN OF Methods Time in Unken (sec) TETRODOTOXIN." Journal of Toxicology •Adult rough-skinned newts were injected 400.00 Toxin Reviews 20(1): 11. with either CORT, ACTH, metyrapone (a [2] Thaker, M. L., Steven L. ; Hews, Diana K. (2009). corticosterone blocker), or a control 200.00 "Acute corticosterone elevation enhances antipredator behaviors in male tree lizard (saline). 0.00 morphs." Hormones and Behavior 56: 51-57. •Each animal was then tapped to stimulate 0 50 100 150 200 250 300 [3] Brodie, E. D. and E. D. Brodie (1990). "Tetrodotoxin a predator attack until they went into Blood levels of Corticosterone (ng/ml) Resistance in Garter Snakes: An Evolutionary Response of Predators to Dangerous Prey." unken. Evolution(3): 651. •Time in unken was recorded and as soon Figure 1. Animals given saline (control) and Metyrapone (CORT blocker) as the animals left unken, blood samples showed similar responses with low CORT levels and higher unken times. were taken. Animals given CORT and ACTH had higher levels of CORT in the blood, ACKNOWLEDGEMENTS •Blood levels of corticosterone were but spent less time in unken. We would like to thank Dr. Edmund D. Brodie, measured using a radioimmunoassay Jr., Tyler Hansen, Gareth Hopkins, Andrew (RIA). Durso, and Geoff Smith, for their assistance and support.