Graduation Year

2011

Document Type

Thesis

Degree

M.S.

Degree Granting Department

Marine Science

Major Professor

Kendra L. Daly

Co-Major Professor

Edward S. Van Vleet

Keywords

Anti-Müllerian hormone, Contaminants, Inhibin, Marine mammal, Reproduction

Abstract

As apex predators in coastal systems, bottlenose dolphins (Tursiops truncatus) are susceptible to persistent organic pollutant (POP) accumulation and retention over time, which has prompted continued interest in understanding the extent to which contaminant body burdens or other stressors are sufficient to cause adverse sublethal effects on energetic fitness, immune function, or reproduction. Increasing our knowledge of reproductive endocrinology in bottlenose dolphins may provide insight into changes in reproductive rates, thereby expanding the capacity to assess conservation status. This study used the Enzyme-Linked ImmunoSorbent Assay (ELISA) technique to examine peptide fertility hormones [inhibin A, inhibin B and anti-Müllerian hormone (AMH)] measured in serum of free-ranging dolphins (n = 129) of varying age, gender, and maturity status from three locations (Sarasota Bay, FL, Indian River Lagoon, FL, and southern Georgia). The primary research objectives were to establish hormone baselines, investigate AMH and inhibin use as reproductive biomarkers, and examine the potential use of these hormones as biomarkers of toxicant or other stressor effects on reproduction. AMH secretion differed significantly with gender (p < 0.001), where levels were approximately 1,000-fold higher in males than females (1,122 ± 427 ng mL-1 and 1.15 ± 1.25 ng mL-1, mean ± SD). Male AMH levels were related to maturity status, and linear regression analysis revealed a significant, negative relationship between male AMH and age, body length, body weight, and maximum girth in all populations. Of the parameters assessed, age was the best indicator of AMH levels in males. AMH concentrations in females did not vary significantly over time or with maturity status, but exhibited a decrease in some older individuals, potentially indicating an AMH decline in long-lived female dolphins. Inhibins did not differ significantly between age classes in males, but appeared to be an estrous cycle indicator in females, where inhibin peaks were likely related to follicular and luteal phases. These data provide new information on circulating serum AMH and inhibin levels in bottlenose dolphins, which appear to reflect a degree of gonadal function and show promise as reproductive biomarkers. Our findings suggest the possibility of toxicant effects on AMH and inhibin production, but not conclusively. Further investigation of mechanism(s) of action for contaminant-related reproductive toxicity will elucidate the diagnostic value of these hormones to assess the effects of POPs on fertility potential in bottlenose dolphins.

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