Chronological monitoring of nutritional and hormonal status of elephant seals through whisker analysis

Abstract

Environmental perturbations impose selection pressures on organisms. The adaptive physiological mechanisms employed by species to survive in their changing environments are fundamental for their persistence. It is postulated that intraspecific variation observed in the reproductive pattern of adult female southern elephant seals (SES, Mirounga leonina) at Marion Island, as well as in other species, is caused by food availability and individual differences in their foraging habits and nutritional status. However, it remains challenging to obtain dietary and physiological data from cryptic organisms at a longitudinal resolution. Sequentially subsampled biologically inert tissues, such as hair, nails, whale baleen, and whiskers (vibrissae) can provide a retrospective biochemical record of the organism. The goal of this dissertation was to develop a biomarker to assess the nutritional and physiological status of free-ranging SES, using chronologically analyzed whiskers sampled from either adult females or their offspring. We combined bulk tissue (whole whisker segment) and amino acid nitrogen (δ15N) isotope values measured chronologically along the length of their whiskers to demonstrate that apart from ecological factors, physiological factors such as fasting, also affects the measured bulk tissue and constituent amino acid-specific δ15N values. In addition, we tested whether the stable isotope values measured in the intrauterine grown tissues of offspring can be utilized as proxies for their mothers’ isotope values during gestation. In contrast to previous studies, we conclusively demonstrated that paired, temporally matched, mother-offspring bulk tissue δ15N and carbon isotope (δ13C) values of SES are not in isotopic equilibrium or linearly correlated during gestation. Also, the relationship between mother-offspring δ15N and δ13C values (Δ) changed as gestation progressed. Fetal development relies primarily on remobilized endogenous maternal proteinaceous sources. We caution against the utilization of offspring bulk tissue stable isotope values to reconstruct the maternal foraging habits. This study represents the first combined bulk-and amino acid-specific stable isotope approach to have investigated the correlation between mother-offspring paired isotope values in mammals.

Lastly, we developed the most comprehensive methodology to date for the non-invasive quantification of endogenously produced compounds extracted from whiskers. Biologically inert keratinous tissues, such as whiskers, are increasingly considered a sought-after minimally-invasive biomatrix that can provide a longitudinal record of the organisms’ steroid hormone levels. The inability to obtain longitudinal hormone data has, for example, hindered investigations into the causes underlying the high rate of reproductive failure observed in marine mammals. To address this knowledge disparity, we have successfully developed and validated the most comprehensive, high-throughput assay to date, quantifying 28 steroids from single whiskers sampled from three seal species in a single chromatographic step, using ultra-performance convergence chromatography-tandem mass spectrometry (UPC2 -MS/MS). The combination of endocrinology, bulk tissue and amino acid-specific stable isotope values, measured chronologically along the length of the whiskers of SES, could provide a better understanding of the ecological and physiological factors that regulate their reproductive fitness. No other technique can currently obtain such information at a longitudinal scale from a non-invasively sampled single tissue matrix that can be sampled once-off.