Abstract

We have validated a novel, reverse-phase high-performance liquid chromatography (RP-HPLC) method that permits rapid and simultaneous quantification of five key reproductive steroids in free-ranging Atlantic bottlenose dolphins, freshwater and sea turtles, and two species of dove.¹ Our results showed that mature females (dolphins, turtles, doves) had higher estradiol (E₂) and progesterone (P₄) levels than testosterone (T₂), while males of reproductive age (dolphins, turtles, doves) consistently had the highest detected concentrations of T₂, and lower detectable concentrations of E₂ and P₄ compared to the females. Juvenile dolphins exhibited the same general trends, although all steroid concentrations were generally lower and did not exhibit the greater ranges of the adult animals. Male bottlenose dolphin concentrations of serum T₂ were comparable to previous studies of male Cetacea as detected by HPLC,^2,3 as were the relative concentration ranges of serum P₄ and E₂ in female bottlenose dolphins as detected by radioimmunoassay (RIA).⁴ Among mature female dolphin samples, E₂ was more predominant than P₄, ranging from 1.0–11.0 µg/mL. Most female P₄ samples ranged from 0.5–2.0 µg/mL, while T₂ only ranged from 0.1–0.57 µg/mL. The majority of male T₂ samples ranged from 1.0–4.0 µg/mL. By contrast, male E₂ concentrations ranged from 0.0–0.59 µg/mL in mature males, while P₄ ranged from 0.0–0.52 µg/mL. Where known from physical characteristics or health exams, gender, reproductive status, and age class were confirmed by HPLC in all tested species, demonstrating that this method allows a snap assessment of the reproductive endocrine status of wild marine life during population and environmental health assessments.

The ability to rapidly and accurately detect the concentrations of multiple steroids in serum, plasma or urine, without regard to sample type or taxa, permits wildlife health experts to build year-to-year endocrine profiles of animals under long-term observation for anthropogenic environmental contaminants and environmental degradation. This method also provides an additional tool for zoo and aquaria managers managing the breeding cycles of different species within their collection. Because the range of dolphin steroid concentrations obtained by HPLC were within published ranges for Atlantic bottlenose dolphins, we conclude that the steroid concentrations found during this study are correct and useful for both managed breeding and wildlife health assessments.

Acknowledgements

Grateful acknowledgement is extended to Dr. Gregory Bossart, Dr. Patricia Fair and Dr. Sarah Milton for support and access to turtle and dolphin samples and data, and to Ms. Ashley Campbell for dove samples.

* Presenting author

Literature Cited

1.  Homer-Drummond S. Parameters Impacting the Reproductive Fitness of Tursiops truncatus (Atlantic Bottlenose Dolphin): Interactions Between Native Endocrinology and Endocrine-Disruptors. [dissertation]. Boca Raton, FL: Florida Atlantic University; 2012.

2.  Kjeld M, Víkingsson G, Alfredsson A, Ólafsson Ö, Árnason A. Sex hormone concentrations in the blood of sei whales (Balaenoptera borealis) off Iceland. J Cetacean Res Manage. 2004;5(3):233–240.

3.  St. Aubin DJ, Schroeder JP. Reproductive aspects of marine mammals. In: Dierauf LA, ed. CRC Handbook of Marine Mammal Medicine: Health, Disease and Rehabilitation. 1st ed. Boca Raton, FL: CRC Press; 1990:353–369.

4.  Sawyer-Steffan JE, Kirby VL, Gilmartin WG. Progesterone and estrogens in the pregnant and nonpregnant dolphin, Tursiops truncatus, and the effects of induced ovulation. Biol Reprod. 1983;28:897–901.