Can The Carbon and Nitrogen Isotope Values of Offspring be Used as a Proxy for Their Mother\u27s Diet? Using Foetal Physiology to Interpret Bulk Tissue and Amino Acid \u3ci\u3eδ\u3c/i\u3e\u3csup\u3e15\u3c/sup\u3eN Values

The measurement of bulk tissue nitrogen (δ15N) and carbon isotope values (δ13C) chronologically along biologically inert tissues sampled from offspring can provide a longitudinal record of their mothers\u27 foraging habits. This study tested the important assumption that mother-offspring stable isotope values are positively and linearly correlated. In addition, any change in the mother-offspring bulk tissues and individual amino acids that occurred during gestation was investigated. Whiskers sampled from southern elephant seal pups (Mirounga leonina) and temporally overlapping whiskers from their mothers were analyzed. This included n = 1895 chronologically subsampled whisker segments for bulk tissue δ15N and δ13C in total and n = 20 whisker segments for amino acid δ15N values, sampled from recently weaned pups (n = 17), juvenile southern elephant seals (SES) \u3c 2 years old (n = 23) and adult female SES (n = 17), which included nine mother-offspring pairs. In contrast to previous studies, the mother-offspring pairs were not in isotopic equilibrium or linearly correlated during gestation: the Δ15N and Δ13C mother-offspring offsets increased by 0.8 and 1.2‰, respectively, during gestation. The foetal bulk δ15N values were 1.7 ± 0.5‰ (0.9-2.7‰) higher than mothers\u27 δ15N values before birth, while the foetal δ13C increased by ~1.7‰ during gestation and were 1.0 ± 0.5‰ (0.0-1.9‰) higher than their mothers\u27 δ13C at the end of pregnancy. The mother-offspring serine and glycine Δ15N differed by ~4.3‰, while the foetal alanine δ15N values were 1.4‰ lower than that of their mothers during the third trimester of pregnancy. The observed mother-offspring δ15N differences are likely explained by shuttling of glutamate-glutamine and glycine-serine amongst skeletal muscle, liver, placenta and foetal tissue. Foetal development relies primarily on remobilized endogenous maternal proteinaceous sources. Researchers should consider foetal physiology when using offspring bulk tissue isotope values as biomarkers for the mother\u27s isotopic composition as part of monitoring programmes

A Multi-Isotope Approach Reveals Seasonal Variation in the Reliance on Marine Resources, Production of Metabolic Water, and Ingestion of Seawater by Two Species of Coastal Passerine to Maintain Water Balance

Tracing how free-ranging organisms interact with their environment to maintain water balance is a difficult topic to study for logistical and methodological reasons. We use a novel combination of triple-oxygen stable isotope analyses of water extracted from plasma (δ16O, δ17O, δ18O) and bulk tissue carbon (δ13C) and nitrogen (δ15N) isotopes of feathers and blood to estimate the proportional contribution of marine resources, seawater, and metabolic water used by two species of unique songbirds (genus Cinclodes) to maintain their water balance in a seasonal coastal environment. We also assessed the physiological adjustments that these birds use to maintain their water balance. In agreement with previous work on these species, δ13C and δ15N data show that the coastal resident and invertivore C. nigrofumosus consumes a diet rich in marine resources, while the diet of migratory C. oustaleti shifts seasonally between marine (winter) to freshwater aquatic resources (summer). Triple-oxygen isotope analysis (Δ17O) of blood plasma, basal metabolic rate (BMR), and total evaporative water loss (TEWL) revealed that ~25% of the body water pool of both species originated from metabolic water, while the rest originated from a mix of seawater and fresh water. Δ17O measurements suggest that the contribution of metabolic water tends to increase in summer in C. nigrofumosus, which is coupled with a significant increase in BMR and TEWL. The two species had similar BMR and TEWL during the austral winter when they occur sympatrically in coastal environments. We also found a positive and significant association between the use of marine resources as measured by δ13C and δ15N values and the estimated δ18O values of ingested (pre-formed) water in both species, which indicates that Cinclodes do not directly drink seawater but rather passively ingest when consuming marine invertebrates. Finally, results obtained from physiological parameters and the isotope-based estimates of marine (food and water) resource use are consistent, supporting the use of the triple-oxygen isotopes to quantify the contribution of water sources to the total water balance of free-ranging birds

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

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.Thesis (PhD (Zoology))--University of Pretoria, 2020.National Research Foundation Society for Marine MammalogyZoology and EntomologyPhD (Zoology)Unrestricte