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' 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) < 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' 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' 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's isotopic composition as part of monitoring programmes.

中文翻译：

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后代的碳和氮同位素值可以用来代替母亲的饮食吗？利用胎儿生理学解释大块组织和氨基酸的δ15N值。

沿子代采样的生物惰性组织按时间顺序测量大块组织氮（δ15N）和碳同位素值（δ13C）可以纵向记录其母亲的觅食习惯。这项研究检验了重要的假设，即母子稳定同位素值呈正相关且线性相关。此外，研究了妊娠过程中母子后体大量组织和单个氨基酸的任何变化。分析了从南部象海豹幼崽（Mirounga leonina）采样的晶须，并分析了其母亲在时间上重叠的晶须。其中包括从散布的幼仔（n = 17）中采样的n = 1895个按时间顺序采样的大块组织δ15N和δ13C晶须片段，n = 20个氨基酸的δ15N晶须片段，小于2岁的南象海豹（SES）（n = 23）和成年雌性SES（n = 17），其中包括9对母子。与以前的研究相反，妊娠期母子对不处于同位素平衡或线性相关：在妊娠期，Δ15N和Δ13C母子偏移分别增加了0.8和1.2‰。胎儿的δ15N值比母亲出生前的δ15N值高1.7±0.5‰（0.9-2.7‰），而胎儿的δ13C在孕期中增加〜1.7‰，比母亲的δ15N值高1.0±0.5‰（0.0-1.9‰）。他们的母亲在怀孕末期的δ13C。母婴的丝氨酸和甘氨酸Δ15N相差约4.3‰，而胎儿的丙氨酸δ15N值比孕晚期的母亲低1.4‰。骨骼肌，肝脏，胎盘和胎儿组织中谷氨酸-谷氨酰胺和甘氨酸-丝氨酸的穿梭可能解释了所观察到的母子δ15N差异。胎儿发育主要依赖于转移的内源性母体蛋白质来源。研究人员在将后代大块组织同位素值用作母亲同位素组成的生物标志物作为监测计划的一部分时，应考虑胎儿生理。