Abstract
Recent studies have demonstrated that some hormones are present in baleen powder from bowhead (Balaena mysticetus) and North Atlantic right (Eubalaena glacialis) whales. To test the potential generalizability of this technique for studies of stress and reproduction in large whales, we sought to determine whether all major classes of steroid and thyroid hormones are detectable in baleen, and whether these hormones are detectable in other mysticetes. Powdered baleen samples were recovered from single specimens of North Atlantic right, bowhead, blue (Balaenoptera [B.]musculus), sei (B. borealis), minke (B. acutorostrata), fin (B. physalus), humpback (Megaptera novaeangliae) and gray (Eschrichtius robustus) whales. Hormones were extracted with a methanol vortex method, after which we tested all species with commercial enzyme immunoassays (EIAs, Arbor Assays) for progesterone, testosterone, 17β-estradiol, cortisol, corticosterone, aldosterone, thyroxine and tri-iodothyronine, representing a wide array of steroid and thyroid hormones of interest for whale physiology research. In total, 64 parallelism tests (8 species × 8 hormones) were evaluated to verify good binding affinity of the assay antibodies to hormones in baleen. We also tested assay accuracy, although available sample volume limited this test to progesterone, testosterone and cortisol. All tested hormones were detectable in baleen powder of all species, and all assays passed parallelism and accuracy tests. Although only single individuals were tested, the consistent detectability of all hormones in all species indicates that baleen hormone analysis is likely applicable to a broad range of mysticetes, and that the EIA kits tested here perform well with baleen extract. Quantification of hormones in baleen may be a suitable technique with which to explore questions that have historically been difficult to address in large whales, including pregnancy and inter-calving interval, age of sexual maturation, timing and duration of seasonal reproductive cycles, adrenal physiology and metabolic rate.
Highlights
Large whales are of interest to conservation biologists due to their key ecological role, unique biological traits and continued low population numbers relative to historic norms (Magera et al, 2013; Atkinson et al, 2015; Thomas and Reeves, 2015)
To test the potential generalizability of this technique for studies of stress and reproduction in large whales, we sought to determine whether all major classes of steroid and thyroid hormones are detectable in baleen, and whether these hormones are detectable in other mysticetes
There were no significant differences in slope between the linear portions of the binding curves of serially diluted baleen extract as compared to pure hormone standards run in the same assay (Figs 1–3, Table 3; note that x-axes of Figs 1–3 show relative dose, not actual dose)
Summary
Large whales are of interest to conservation biologists due to their key ecological role, unique biological traits (e.g. large body size, long lifespan) and continued low population numbers relative to historic norms (Magera et al, 2013; Atkinson et al, 2015; Thomas and Reeves, 2015). Conservation biologists routinely employ endocrine techniques for non-plasma sample types that are more garnered than blood, including such sample types as faeces, hair and feather (Schwarzenberger, 2007; Sheriff et al 2011; Terwissen et al, 2014; Dettmer et al, 2015; Romero and Fairhurst, 2016) Such approaches often focus on the steroid hormones and to a lesser degree the thyroid hormones; steroid and thyroid hormones are highly conserved across vertebrates (i.e. unlike many peptide hormones; Miller, 2005; Kawauchi and Sower, 2006), do not degrade rapidly, and are known to be deposited in a wide assortment of body tissues (Bentley, 1998; Amaral, 2010). Thyroid hormone studies on wildlife usually focus either on tri-iodothyronine (T3), the active hormone in tissues, and/or its immediate precursor thyroxine (T4), the major circulating pro-hormone (Bentley, 1998)
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