Remote blubber sampling paired with liquid chromatography tandem mass spectrometry for steroidal endocrinology in free-ranging bottlenose dolphins (Tursiops truncatus)

Abstract

Liquid chromatography tandem mass spectrometry allows for the measurement of steroid hormone suites in the blubber of marine mammals. By combining this technology with minimally invasive techniques such as remote biopsy, endocrine profiles can be assessed, allowing for studies of hormonal profile variation over time. In this study, we explored associations among different steroidogenic pathways and seasonal differences in blubber hormone profiles of free-ranging common bottlenose dolphins along the coast of South Carolina, USA. Male dolphins experience a peak in testosterone, androstenedione, progesterone, and 17-hydroxyprogesterone in the spring, likely related to an upregulation of the androgen steroidogenic pathway during mating season. We also observed increased cortisol concentrations during summer compared to winter. Among females, there was an increase in androstenedione with elevated progesterone concentrations indicative of pregnancy, highlighting another potential endocrine marker for pregnancy in free-ranging dolphins. This work emphasizes the importance of selecting the appropriate season for studies on endocrine status to effectively uncover physiological variation or disruption in free-ranging cetaceans.

Keywords: Blubber; Cetacean; Hormones; Remote biopsy; Reproductive steroids; Stress.

Figure 1:

Map of the Ashepoo, Combahee, Edisto Basin (ACE) and the Charleston Area Waterways System (CAWS) where common bottlenose dolphin remote blubber biopsies were collected. Each dot represents the GPS locations at which an individual was biopsied.

Figure 2:

Boxplots of blubber hormone concentrations from all common bottlenose dolphins sampled in this study on the Ashepoo, Combahee, Edisto Basin and surrounding Charleston-area waterways in South Carolina. Boxplots represent the median with quartiles. The lower solid black bar represents the reporting limit for this method. Detection frequencies for each hormone are listed by sex above the x-axis.

Figure 3:

Relationships among hormones in blubber from common bottlenose dolphins. Panel A: The steroid synthesis pathway and classification for hormones measured in this study. Panel B: Correlations heat map using Kendall’s Tau. Intensity approximates tau. Statistical significance (p < 0.05) is represented by (+) for a positive tau and (−) for a negative tau. Spaces are white where no information is available. Sample sizes were 81 for males and 12 for females. Panel C: Principal components analysis of quantified blubber hormones for male common bottlenose dolphins.

Figure 3:

Relationships among hormones in blubber from common bottlenose dolphins. Panel A: The steroid synthesis pathway and classification for hormones measured in this study. Panel B: Correlations heat map using Kendall’s Tau. Intensity approximates tau. Statistical significance (p < 0.05) is represented by (+) for a positive tau and (−) for a negative tau. Spaces are white where no information is available. Sample sizes were 81 for males and 12 for females. Panel C: Principal components analysis of quantified blubber hormones for male common bottlenose dolphins.

Figure 3:

Relationships among hormones in blubber from common bottlenose dolphins. Panel A: The steroid synthesis pathway and classification for hormones measured in this study. Panel B: Correlations heat map using Kendall’s Tau. Intensity approximates tau. Statistical significance (p < 0.05) is represented by (+) for a positive tau and (−) for a negative tau. Spaces are white where no information is available. Sample sizes were 81 for males and 12 for females. Panel C: Principal components analysis of quantified blubber hormones for male common bottlenose dolphins.

Figure 4:

Comparison of seasonal blubber hormone concentrations in male common bottlenose dolphins. Sample sizes for each season were as follows: Winter n = 18, Spring n = 14, Summer n = 33, Fall n = 16. Significant differences assessed by post-hoc analysis are indicated by different letters.