Latent trait-like component identified for bottlenose dolphin fecal glucocorticoid metabolite concentrations

Cortisol, an end product of hypothalamic-pituitary-adrenal (HPA) axis activation, plays a critical role in responding to arousal and restoring homeostasis. Chronic or repeated activation of the HPA axis may lead to physiological dysregulation that has potential negative health consequences. Quantifying stable, trait-like components of fecal glucocorticoid metabolite concentrations in animals could have a marked effect on investigating physiological stress responses and establishing higher resolution baselines for intra-individual clinical management, yet no studies have examined latent state-trait (LST) models for any non-human animals. Using an LST model, trait and state sources of fecal glucocorticoid metabolite variation were decomposed. Fecal samples were collected from 179 common bottlenose dolphins (Tursiops truncatus) in 41 habitats in late afternoon. The fit indices were excellent suggesting that LST models can be applied to bottlenose dolphin glucocorticoid metabolite measures. Trait factors (i.e., individual specific) accounted for an estimated 49 % of the variance in glucocorticoid metabolite concentrations and state factors (i.e., day-to-day factors) accounted for an estimated 41 % of the variance. This work suggests that LST models provide valuable evidence of a trait-like component in glucocorticoid metabolites in bottlenose dolphins that can be widely used in clinical management and research settings.