Measuring Stress and Reproductive Hormones in Dolphins with UHPLC

Measuring Stress and Reproductive Hormones in Dolphins with UHPLC

John Chasse

SUMMARY: A recent study measured stress and reproductive hormones in three stocks of free-ranging bottlenose dolphins inhabiting different natural salinities across the Gulf of Mexico, with hormones extracted from the blubber of 82 remotely biopsied dolphins and quantified using ultrahigh-pressure liquid chromatography (UHPLC) coupled with orbital ion trap fusion mass spectrometry.

A recent study conducted by scientists from the Texas A&M University-Corpus Christi, Hydrosphere (Monroe, North Carolina) and the Southeast Fisheries Science Center (Pascagoula, Mississippi) measured stress hormones (aldosterone, corticosterone, cortisol, and cortisone) and reproductive hormones (progesterone and testosterone) in three stocks of free-ranging bottlenose dolphins (Tursiops truncatus) inhabiting different natural salinities across the Gulf of Mexico. Hormones were extracted from the blubber of 82 remotely biopsied dolphins and quantified using ultrahigh-pressure liquid chromatography (UHPLC) coupled with orbital ion trap fusion mass spectrometry (MS). A positive correlation was found between cortisol and salinity, and aldosterone, quantified in dolphin blubber for the first time, was detected across the salinity gradient but was not significantly related to salinity levels. Concentrations of testosterone were found to be seasonally variable. This study enhances our understanding of how climate changes and extensive anthropogenic stressors challenge homeostasis in a marine bioindicator species. A paper resulting from this work was published in ACS Omega (1).

As climate change intensifies extremes of salinity in their environment (2,3), there is an increasing need to the need to understand how dolphins regulate major physiological processes in highly variable environments increases. Blubber, by being the only matrix in which aldosterone has not yet been quantified in bottlenose dolphins (4,5), limits our knowledge of how aldosterone regulates osmotic balance. To explore the endocrine response of dolphins to variable salinities, the researchers measured stress and reproductive hormones in dolphin blubber across a salinity gradient spanning the northwestern Gulf of Mexico. Hormones were assessed relative to the salinity level, water temperature, dolphin sex, season, and year.

Prior to the research, the team predicted that corticosteroids (cortisol, corticosterone, and cortisone) and aldosterone would be positively correlated with high and low salinities due to increased osmotic pressures (6), and this prediction was confirmed. A verified relationship between salinity and reproductive hormones was not foreseen; however, a variation of reproductive hormones depending on the season was expected (7) and was observed. The researchers furthermore predicted that stress hormone levels in samples collected from the same dolphin stock over the years would increase over time resulting from the expansion of industrial development and human activity during that period (8).

Understanding the impacts of environmental change on bioindicator species such as bottlenose dolphins can assist in the sustainable management of at-risk dolphin stocks, as well as identify concerns of ecosystem health, according to the authors. Specifically, quantification of aldosterone in dolphin blubber marks a crucial step in the advancement of understanding how dolphins regulate physiological homeostasis across highly variable environmental contexts. The positive correlation between cortisol and salinity suggests a disruption of the osmotic balance, as well as a subsequent need for increased aldosterone production across a salinity gradient. The simultaneous assessment of reproductive hormones in this study provides the additional context necessary for interpreting the level and source of stress in free-ranging dolphins. Hormone concentrations determined from remotely biopsied blubber samples can be informative of reproductive events and large-scale environmental change; the authors believe this should be further warranted to monitor the health of free-ranging dolphins and the ecosystems they inhabit (1).

Dolphin. © Photo&Lightroom LF - stock.adobe.com

References

1. Guinn, M. A.; Elliott, J. Y.; Wittmaack, C. S.; Sinclair, C.; Abdulla, H. A.; Orbach, D. N. Stress and Reproductive Hormones of Free-Ranging Dolphins Across a Natural Salinity Gradient. ACS Omega 2024, 9 (45), 45068-45079. DOI: 10.1021/acsomega.4c05466

2. Ummenhofer, C. C.; Meehl, G. A. Extreme Weather and Climate Events with Ecological Relevance: A Review. Philosophical Transactions of the Royal Society B: Biological Sciences 2017, 372 (1723), 20160135. DOI: 10.1098/rstb.2016.0135

3. Tweedley, J. R.; Dittmann, S. R.; Whitfield, A. K.; Withers, K.; Hoeksema, S. D.; Potter, I. C. Hypersalinity: Global Distribution, Causes, and Present and Future Effects on the Biota of Estuaries and Lagoons. In Coasts and Eestuaries; Elsevier, 2019; pp 523– 546

4. Champagne, C. D.; Kellar, N. M.; Trego, M. L.; Delehanty, B.; Boonstra, R.; Wasser, S. K.; Booth, R. K.; Crocker, D. E.; Houser, D. S. Comprehensive Endocrine Response to Acute Stress in the Bottlenose Dolphin from Serum, Blubber, and Feces. Gen. Comp. Endrocrinol. 2018, 266, 178– 193, DOI: 10.1016/j.ygcen.2018.05.015

5. Bechshoft, T.; Wright, A. J.; Styrishave, B.; Houser, D. Measuring and Validating Concentrations of Steroid Hormones in the Skin of Bottlenose Dolphins (Tursiops truncatus). Conserv. Physiol. 2020, 8 (1), coaa032 DOI: 10.1093/conphys/coaa032

6. McClain, A. M.; Daniels, R.; Gomez, F. M.; Ridgway, S. H.; Takeshita, R.; Jensen, E. D.; Smith, C. R. Physiological Effects of Low Salinity Exposure on Bottlenose Dolphins (Tursiops truncatus). Journal of Zoological and Botanical Gardens 2020, 1 (1), 61– 75, DOI: 10.3390/jzbg1010005

7. Galligan, T. M.; Boggs, A. S. P.; Balmer, B. C.; Rowles, T.; Smith, C. R.; Townsend, F.; Wells, R. S.; Kellar, N. M.; Zolman, E. S.; Schwacke, L. H. Blubber Steroid Hormone Profiles as Indicators of Physiological State in Free-Ranging Common Bottlenose Dolphins (Tursiops truncatus). Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology 2020, 239, 110583 DOI: 10.1016/j.cbpa.2019.110583