Adrenal Hormones in Common Bottlenose Dolphins (Tursiops truncatus): Influential Factors and Reference Intervals

Abstract

Inshore common bottlenose dolphins (Tursiops truncatus) are exposed to a broad spectrum of natural and anthropogenic stressors. In response to these stressors, the mammalian adrenal gland releases hormones such as cortisol and aldosterone to maintain physiological and biochemical homeostasis. Consequently, adrenal gland dysfunction results in disruption of hormone secretion and an inappropriate stress response. Our objective herein was to develop diagnostic reference intervals (RIs) for adrenal hormones commonly associated with the stress response (i.e., cortisol, aldosterone) that account for the influence of intrinsic (e.g., age, sex) and extrinsic (e.g., time) factors. Ultimately, these reference intervals will be used to gauge an individual’s response to chase-capture stress and could indicate adrenal abnormalities. Linear mixed models (LMMs) were used to evaluate demographic and sampling factors contributing to differences in serum cortisol and aldosterone concentrations among bottlenose dolphins sampled in Sarasota Bay, Florida, USA (2000–2012). Serum cortisol concentrations were significantly associated with elapsed time from initial stimulation to sample collection (p<0.05), and RIs were constructed using nonparametric methods based on elapsed sampling time for dolphins sampled in less than 30 minutes following net deployment (95% RI: 0.91–4.21 µg/dL) and following biological sampling aboard a research vessel (95% RI: 2.32–6.68 µg/dL). To examine the applicability of the pre-sampling cortisol RI across multiple estuarine stocks, data from three additional southeast U.S. sites were compared, revealing that all of the dolphins sampled from the other sites (N = 34) had cortisol concentrations within the 95th percentile RI. Significant associations between serum concentrations of aldosterone and variables reported in previous studies (i.e., age, elapsed sampling time) were not observed in the current project (p<0.05). Also, approximately 16% of Sarasota Bay bottlenose dolphin aldosterone concentrations were below the assay’s detection limit (11 pg/mL), thus hindering the ability to derive 95th percentile RIs. Serum aldosterone concentrations from animals sampled at the three additional sites were compared to the detection limit, and the proportion of animals with low aldosterone concentrations was not significantly different than an expected prevalence of 16%. Although this study relied upon long-term, free-ranging bottlenose dolphin health data from a single site, the objective RIs can be used for future evaluation of adrenal function among individuals sampled during capture-release health assessments.

Fecal glucocorticoids and anthropogenic injury and mortality in North Atlantic right whales Eubalaena glacialis

“…Aubin & Dierauf 2001). It was also higher than cortisol levels reported in most cetaceans subjected to capture stress, although methodological differences may invalidate direct comparisons (Thomson & Geraci 1986, Orlov et al 1991, St. Aubin et al 1996, Suzuki et al 1998, Kjeld 2001, Schmitt et al 2010, Fair et al 2014, Hart et al 2015. Stranded whales experience gradual respiratory and cardiovascular collapse (without their neutral buoyancy in seawater), along with blistered skin, hyperthermia, and being scavenged on while alive (by gulls in this case), resulting in severe distress (Harms et al 2014).…”

Slow recovery of Barataria Bay dolphin health following the Deepwater Horizon oil spill (2013-2014), with evidence of persistent lung disease and impaired stress response

“…Four sets of reference intervals were used to evaluate the health of BB, SB, and MS dolphins: (1) hematology (Schwacke et al 2009), (2) serum chemistry (Schwacke et al 2009), (3) body condition (Hart et al 2013), and (4) cortisol (Hart et al 2015). reported hematological and serum biochemical abnormalities grouped by health panels (i.e.…”

“…Similarly, body condition for each animal was determined based on reference intervals for mass:length ratio as described in Hart et al (2013) and Schwacke et al (2014), where non-pregnant individuals with a mass:length ratio below the lower reference threshold were considered to be in poor body condition. Subsequent to the Schwacke et al (2014) study, 95 th percentile reference intervals have been constructed for bottlenose dolphin cortisol concentrations in serum collected during the pre-and post-sampling bleeds (Hart et al 2015). These reference intervals were used to re-evaluate the serum cortisol concentrations of SB and BB dolphins sampled in 2010−2011, as well as detect cases among the SB 2013, BB 2013, BB 2014, and MS 2013 Only samples collected in < 30 min elapsed time of net deployment were used for pre-sampling reference interval evaluations (Hart et al 2015).…”

“…Subsequent to the Schwacke et al (2014) study, 95 th percentile reference intervals have been constructed for bottlenose dolphin cortisol concentrations in serum collected during the pre-and post-sampling bleeds (Hart et al 2015). These reference intervals were used to re-evaluate the serum cortisol concentrations of SB and BB dolphins sampled in 2010−2011, as well as detect cases among the SB 2013, BB 2013, BB 2014, and MS 2013 Only samples collected in < 30 min elapsed time of net deployment were used for pre-sampling reference interval evaluations (Hart et al 2015). Postsampling cortisol was unavailable for SB dolphins sampled in 2010−2011 or BB 2011 dolphins, as postsampling blood was not collected.…”

“…Postsampling cortisol was unavailable for SB dolphins sampled in 2010−2011 or BB 2011 dolphins, as postsampling blood was not collected. Aldosterone concentrations were compared to the assay detection limit, as outlined in Hart et al (2015).…”