Multi-year longitudinal profiles of cortisol and corticosterone recovered from baleen of North Atlantic right whales (Eubalaena glacialis)

Abstract

Research into stress physiology of mysticete whales has been hampered by difficulty in obtaining repeated physiological samples from individuals over time. We investigated whether multi-year longitudinal records of glucocorticoids can be reconstructed from serial sampling along full-length baleen plates (representing ~10 years of baleen growth), using baleen recovered from two female North Atlantic right whales (Eubalaena glacialis) of known reproductive history. Cortisol and corticosterone were quantified with immunoassay of subsamples taken every 4 cm (representing ~60 d time intervals) along a full-length baleen plate from each female.In both whales, corticosterone was significantly elevated during known pregnancies (inferred from calf sightings and necropsy data) as compared to intercalving intervals; cortisol was significantly elevated during pregnancies in one female but not the other. Within intercalving intervals, corticosterone was significantly elevated during the first year (lactation year) and/or the second year (post-lactation year) as compared to later years of the intercalving interval, while cortisol showed more variable patterns. Cortisol occasionally showed brief high elevations ("spikes") not paralleled by corticosterone, suggesting that the two glucocorticoids might be differentially responsive to certain stressors. Generally, immunoreactive corticosterone was present in higher concentration in baleen than immunoreactive cortisol; corticosterone:cortisol ratio was usually >4 and was highly variable in both individuals. Further investigation of baleen cortisol and corticosterone profiles could prove fruitful for elucidating long-term, multi-year patterns in stress physiology of large whales, determined retrospectively from stranded or archived specimens. Hunt et al. -Baleen Hormones 3 HIGHLIGHTS• Immunoreactive cortisol and corticosterone are detectable in whale baleen• Single baleen plates contain multi-year longitudinal time series of glucocorticoids• Glucocorticoids tend to be elevated in baleen growth coincident with pregnancy• Corticosterone was present in baleen at much greater concentration than cortisol

Chronic stress from fishing gear entanglement is recorded in baleen from a bowhead whale (Balaena mysticetus)

“…Immunoreactive cortisol and corticosterone were both measurable in baleen from 17B6, and baseline corticosterone concentrations were over 3-fold higher than baseline cortisol. This is consistent with other recent studies of GCs in baleen, in which corticosterone concentrations were up to 4-fold higher than cortisol in baleen (Hunt et al 2017aLysiak et al 2018). Although the specific mechanisms for deposition of circulating GCs into baleen have not been determined, the different physicochemical properties of the two glucocorticoids undoubtedly affects both accumulation and retention of the two GCs in the baleen matrix.…”

“…Variation in baleen GCs associated with energetically demanding life history stages such as pregnancy and lactation has been reported in E. glacialis (Hunt et al . ). Additional steroid and thyroid hormones have also been extracted and quantified in baleen from mysticete whales (Hunt et al .…”

“…This is consistent with other recent studies of GCs in baleen, in which corticosterone concentrations were up to 4‐fold higher than cortisol in baleen (Hunt et al . , ; Lysiak et al . ).…”

“…Fernández Ajó et al (2018) attributed postnatal increases in baleen GCs to chronic stress from repeated wounding by kelp gulls (Larus dominicanus) in two southern right whale calves (E. australis). Variation in baleen GCs associated with energetically demanding life history stages such as pregnancy and lactation has been reported in E. glacialis (Hunt et al 2017a). Additional steroid and thyroid hormones have also been extracted and quantified in baleen from mysticete whales (Hunt et al 2017b), potentially expanding insights into reproductive physiology, metabolic activity, and nutritional status.…”

Are we overestimating the utility of hair glucocorticoids? A systematic review exploring the empirical evidence supporting hair glucocorticoids as a measure of stress

“…To our knowledge, it is currently all but completely unknown whether the hydrophobic interactions between a steroid hormone and the keratin of a strand of hair are strong enough to lock the molecules permanently in place. Convincing evidence that baleen from whales can trap hormones, leaving a historical record of hormonal fluctuations, has been presented 81,82 . A similar case for hair -a distantly related keratinous matrix -remains elusive however.…”