青藏高原3种常见鸟类卵壳膜稳定碳、氮同位素组成特征

本文测定了青藏高原3种常见鸟类——普通鸬鹚Phalacrocorax carbo、渔鸥Larus ichthyaetus和小云雀Alauda gulgula卵壳膜的δ13C、δ15N,同时结合相关文献同物种肌肉组织中的δ13C、δ15N数据,探讨了卵壳膜代替肌肉作为稳定同位素载体的可行性。结果表明,小云雀、普通鸬鹚和渔鸥卵壳膜的δ13C分别为-20.80‰±0.48‰、-23.29‰±0.35‰和-24.20‰±0.33‰,而δ15N分别为9.25‰±0.87‰、14.40‰±1.03‰和13.94‰±0.43‰。单因素方差分析结果显示:3个物种卵壳膜δ13C、δ15N差异均具有高度统计学意义(P<0.01)。其中,δ13C值小云雀相对于普通鸬鹚偏正,普通鸬鹚相对于渔鸥偏正;普通鸬鹚与渔鸥之间δ15N值差异无统计学意义,但二者相对于小云雀显著偏正。因此,我们认为在一些问题的研究中卵壳膜可以代替肌肉组织作为稳定同位素的载体。     

三峡库区小江库湾鱼类食物网的稳定C、N同位素分析

应用稳定碳(δ₁₃C)、氮(δ₁₅N)同位素探讨了三峡库区一级支流小江库湾枯水期(2010.7)和丰水期间(2010.12)鱼类食物网结构。研究结果显示：初级生产者颗粒有机物(POM)和固着藻类δ₁₃C、δ₁₅N值范围分别为-23.33‰～-21.05‰、-25.13‰～-24.54‰,3.99‰～6.25‰、4.64‰～4.79‰。POM和固着藻类构成了小江库湾食物网能量的主要来源,其中丰水期间陆生营养物质输入是其食物网能量来源的一种重要补充途径。小江库湾常见鱼类食性可分为杂食偏植物食性、杂食偏动物食性及动物食性3种营养类群。在不同时期(枯水期和丰水期)小江库湾鱼类食物网营养级长度均有三级并且存在4种主要营养路径,表明了在三峡工程运行初期小江库湾已经形成了相对稳定的食物网结构。研究为小江库湾鱼类资源管理及生态系统恢复提供了一定的指导意义。     

基于碳、氮稳定同位素的厦门筼筜湖两种优势端足类食性分析

测定了厦门市筼筜湖(内、外湖)大型海藻群落两种优势端足类(强壮藻钩虾Ampitheoe valida和上野蜾蠃蜚Corophium uenoi)及其潜在食源的碳、氮稳定同位素比值(δ~(13)C和δ~(15)N),分析研究了这两种端足类摄食习性的空间变动特征。研究发现,端足类的潜在食源包括悬浮颗粒有机物(Particulate organic matter:POM),沉积有机物(Sedimentary organic matter:SOM),石莼(Ulva lactuca:Ulva)及其表面的附生生物(Epiphytes:Epi),它们的δ~(13)C和δ~(15)N值分别介于-24.0‰(POM)—-11.8‰(Ulva)和-1.7‰(POM)—4.7‰(Ulva)之间。其中,Ulva和POM的δ~(13)C值的内、外湖差异不显著;而外湖SOM和Epi的δ~(13)C值则明显高于内湖。采样区SOM有机质来源的空间差异是其δ~(13)C内、外湖差异的主要原因。除POM外,外湖有机碳源的δ~(15)N明显高于内湖,这与它们利用氮源的δ~(15)N的差异有关。潜在食源稳定同位素组成的空间差异,使得筼筜湖端足类的稳定同位素组成,尤其是δ~(15)N值表现出显著的空间变动特征(强壮藻钩虾和上野蜾蠃蜚δ~(15)N的内、外湖差异高达1.6‰和4.2‰,变幅约1个营养级),但2种端足类食性的空间差异却不尽相同:强壮藻钩虾的食性相对稳定,其δ~(13)C值介于Ulva和Epi之间,表明它主要从Ulva及其表面的Epi获取碳源;而上野蜾蠃蜚的食性内、外湖差异较大:内湖从石莼表面的Epi获取碳源,约20%是来自POM的贡献,而外湖则主要以Ulva及其表面的Epi为食。分析显示,筼筜湖内、外湖端足类δ~(15)N的空间差异并不是端足类的营养级发生了变化,而是由于端足类食源δ~(15)N的空间差异引起的,而不同端足类食性的内、外湖差异则可能与环境中饵料的丰度和生物量密切相关。     

应用碳氮稳定同位素技术研究江豚(Neophocaena asiaeorientalis ssp. sunameri)食性

稳定同位素技术已广泛地用于分析生态系统中食物网的食物来源和营养级关系,但在海洋哺乳动物食性方面应用较少。通过分析2012年4—6月在辽东湾沿岸海域搁浅而死亡的江豚样本和同时期(6月)取自辽东湾海域主要渔获物的碳氮稳定同位素比值,研究了江豚(Neophocaena asiaeorientalis ssp.sunameri)及其可能摄食饵料的碳氮稳定同位素组成。结果表明:江豚δ13C值为(-18.4±0.3)‰,δ15N值为(13.8±0.4)‰。28种可能生物饵料的δ13C值的范围为-19.5‰—-17.0‰,δ~(15)N值的范围为11.4‰—14.0‰。江豚的营养级为4.5,高于传统胃含物分析法的研究结果。28种测试生物的营养级位于3.8—4.6之间。江豚的食物来源主要以鱼类为主,对食物种类的喜食顺序为中上层鱼类中下层鱼类底层鱼类头足类虾类蟹类,其平均贡献率分别为43.9%、18.2%、13.1%、10.0%、8.8%、6.0%。江豚碳氮稳定同位素比值与体长无明显的线性关系,碳营养源较为稳定,氮营养源复杂多变。     

枸杞岛近岸海域食物网的稳定同位素分析

为了探明岛礁近岸海域食物网主要生物类群之间的营养关系,对2012年11月和2013年2月枸杞岛近岸的消费者及其潜在食物源的稳定碳、氮同位素组成进行了分析,并利用氮稳定同位素数据计算了消费者的营养级。结果表明:枸杞岛近岸海域消费者潜在食源浮游植物、POM、SOM和大型海藻的δ13C值范围为-21.7‰~-14.7‰,浮游动物、大型无脊椎动物和鱼类等消费者的δ13C值范围为-21.1‰~-13.7‰。初级生产者的C/N平均值为8.5,消费者的C/N平均值3.7,差异极显著(P0.001)。根据消费者的δ15N值,可将枸杞岛近岸海域的消费者分为滤食性浮游动物、食藻或碎屑的小型底栖动物、杂食性的大型无脊椎动物和鱼类以及凶猛的肉食性鱼类4大类,消费者共有4个营养等级,黑鲷的营养级最高为4.33。     

草海湿地食物链稳定碳氮同位素特征与食物链结构

以国家级自然保护区贵州威宁草海为研究对象,利用稳定同位素技术,分析草海湿地食物链碳(δ~(13)C)、氮(δ15N)同位素特征,计算各生物类群营养级别,建立草海食物链结构。结果表明:草海湿地生态系统中δ13C比值范围为-27.56‰～-13.25‰(均值±标准差,-21.52‰±3.61‰);δ15N值范围为0.32‰～15.14‰(8.69‰±3.92‰),δ13C与δ15N呈显著负相关(r=-0.423,P0.01)。草海湿地食物链中消费者营养级处于0.8～3.7,其中:鱼类营养级为0.8～2.5,相对其他地区偏低;底栖动物营养级为2.0～2.8,鸟类营养级为1.0～3.7。鱼类和底栖动物的营养级别均表现为肉食性杂食性植食性。草海食物链结构复杂,主要的两条碳流动途径分别为:底泥和浮游植物→浮游动物→鱼类→鸟类以及水生植物→鱼类和鸟类。     

基于胃含物分析和稳定同位素技术研究鳀的摄食生态

鳀是重要的渔业资源捕捞对象,同时也是生态系统营养动力学研究的关键种。基于2020年和2008—2009年东海区采集的鳀样品,结合胃含物分析和肌肉碳、氮稳定同位素技术,分析了鳀的食物组成、食性昼夜差异、不同发育阶段的食性转变及其营养级,研究鳀的摄食生态。胃含物分析显示,鳀主要摄食浮游甲壳类和小型鱼类,优势饵料依次为太平洋磷虾[相对重要指数百分比(IRI)=87.6%,出现频率(F)=57.6%]、小拟哲水蚤(IRI=3.2%,F=15.3%)和细足法虫戎(IRI=2.1%,F=13.1%);同位素分析显示,桡足类是鳀的主要食物来源,其次是磷虾类,端足类的食源贡献率最小,不足1%。鳀食物组成昼夜差异明显,摄食强度白天比晚上高,下午最高,午夜最低;叉长90 mm是鳀食性转变的拐点,小于90 mm的鳀主要摄食浮游动物,大于90 mm的鳀主要摄食浮游动物,兼食小型鱼类。鳀的δ¹³C值范围为-21.66‰～-18.14‰,平均值为(-19.92±0.86)‰;δ¹⁵N值范围为4.07‰～10.78‰,平均值为(8.14±2.48)‰;鳀的δ¹³C和δ¹⁵N比值与叉长呈极显著正相关。基于胃含物分析的鳀营养级为3.4,基于δ¹⁵N稳定同位素的鳀营养级为2.7。本研究可为中上层小型鱼类在生态系统中的营养地位提供参考依据,为构建食物网营养通道提供基础资料。     

冶金区节肢动物碳、氮稳定同位素组成及营养级关系

通过测定辽宁省葫芦岛锌厂不同生境植物和主要消费者的碳、氮稳定同位素比值,研究冶金区不同消费者碳、氮稳定同位素组成及不同消费者之间的关系.结果表明:节肢动物δ13C、δ15N值的变化范围分别为-12.61‰～-29.63‰、1.73‰～9.94‰,变化幅度较大.研究区植物以C3植物居多,导致不同群落生境动物δ13C值较低;螳螂、蜘蛛δ15N比值高于其他动物;通过营养级模型计算可知不同消费者之间的关系,蝗虫、蚱蜢等草食性动物形成第二营养级,即初级消费者;第三营养级包括蜘蛛、螳螂,为次级消费者.     

利用碳氮稳定同位素技术分析东海银鲳食性

利用稳定同位素技术分析了东海银鲳(Pampus argenteus)及其可能摄食饵料的碳、氮稳定同位素比值,以期探讨东海银鲳可能的食物来源.结果表明:东海区银鲳平均碳(813C)和氮(δ15N)稳定同位素比值分别为-18.22‰、8.16‰,其可能摄食饵料的δ13C值变化范围为-17.33‰～-21.58‰,差值为4.25‰,δ15N值变化范围为3.89‰～7.96‰,差值为4.07‰;东海银鲳可能的食物来源主要为箭虫、虾类、水母类、头足类、仔稚鱼和浮游动物等,其中箭虫为主要可能的食物来源,其贡献率为24%～78%,平均贡献率为57%;银鲳可能摄食的其他饵料中,贡献率从大到小依次为虾类、水母类、头足类、仔稚鱼、＞1000 μm浮游动物、500～1000 μm浮游动物和100～500 μm浮游动物,其平均贡献率分别为11.8%、8.4%、7.1%、5.0%、4.9%、3.2%和2.6%.由以上结果可知,银鲳是一种广食性鱼类,其饵料种类较多,碳和氮的来源均较为复杂.     

岩溶区不同植被类型下的土壤氮同位素分异特征

利用氮同位素自然丰度(δ¹⁵N)法研究了重庆青木关岩溶区不同植被类型下的土壤氮同位素分异特征及其影响因素。研究结果表明区内土壤δ¹⁵N受不同的植被、地质和土地利用等影响而具有明显的横向和垂向分异特征,具体表现为:0-20 cm层土壤δ¹⁵N与植物体δ¹⁵N具有显著相关性,该层土壤δ¹⁵N大小为草地土(4.79‰)> 退耕还林土(4.77‰)> 稻田土(4.28‰)> 旱地土(4.25‰)> 灌丛土(3.82‰)> 针叶林土(3.81‰)> 砂岩区针叶林土(3.40‰);20-40 cm层土壤δ¹⁵N大小为砂岩区针叶林土(5.21‰)> 退耕还林土(5.10‰)> 草地土(5.01‰)> 稻田土(4.88‰)>灌丛土(4.70‰)>旱地土(4.55‰)> 针叶林土(4.26‰);40 cm以下土壤δ¹⁵N差异较小,灌丛最高,旱地最低。总体上,砂岩区林地土壤除表层贫化¹⁵N外,其余各层均富集¹⁵N,且分异较小。而岩溶区土壤δ¹⁵N具有明显的垂直变异特征,特别是灌丛林,表现为40 cm以上的土壤贫化¹⁵N,且变化较大,其中0-10 cm土壤δ¹⁵N受植物凋落物影响而较低,10-20 cm土壤δ¹⁵N受微生物作用影响稍显偏高,20-30 cm土壤δ¹⁵N随微生物活动减弱而有所降低;40 cm以下土壤矿化程度较大而富集¹⁵N,且变化较小。除受植被类型影响外,岩溶区土壤δ¹⁵N还受其偏碱、富钙、高粘粒含量的物理化学特性以及农业施肥活动等因素共同影响。     

Tissue turnover and stable isotope clocks to quantify resource shifts in anadromous rainbow trout

Stable isotopes can illuminate resource usage by organisms, but effective interpretation is predicated on laboratory validation. Here we develop stable isotope clocks to track resource shifts in anadromous rainbow trout (Oncorhynchus mykiss). We used a diet-switch experiment and model fitting to quantify N stable isotope (δ¹⁵N) turnover rates and discrimination factors for seven tissues: plasma, liver, fin, mucus, red blood cells, muscle, and scales. Among tissues, diet-tissue δ¹⁵N discrimination factors ranged from 1.3 to 3.4 ‰. Model-supported tissue turnover half-lives ranged from 9.0 (fin) to 27.7 (scale) days. We evaluated six tissue turnover models using Akaike’s information criterion corrected for small sample sizes. The use of equilibrium tissue values was supported in all tissues and two-compartment models were supported in plasma, liver, and mucus. Using parameter estimates and their uncertainty we developed stable isotope clocks to estimate the time since resource shifts. Longer turnover tissues provided accurate estimates of time since resource switch for durations approximately twice their half-life. Faster turnover tissues provided even higher precision estimates, but only within their half-life post-switch. Averaging estimates of time since resource shift from multiple tissues provided the highest precision estimates of time since resource shift for the longest duration (up to 64 days). This study therefore provides insight into physiological processes that underpin stable isotope patterns, explicitly tests alternative models, and quantifies key parameters that are the foundation of field-based stable isotope analysis.     

中国古代儿童断奶模式与喂养方式初探——以安徽薄阳城遗址人骨的C、N稳定同位素分析为例

了解古代儿童的断奶模式和喂养方式,可望为揭示古代儿童的营养状况、生长发育以及其死亡原因提供有价值的重要信息。近些年来,通过对古代儿童骨骼的C、N稳定同位素分析,重建古代儿童的断奶模式和喂养方式,成为国际生物考古界的研究前沿,但在我国尚无任何相关报道。为此,本文以安徽滁州薄阳城遗址人骨(包含不同年龄阶段的儿童和成年人)样品为研究材料,通过对同一个体肋骨和肢骨的C、N稳定同位素分析和比较,重点探讨了我国西周时期儿童的断奶模式及喂养方式。研究结果显示:儿童在2岁已有辅食的摄入,大多数儿童在3-4岁已经完成断奶;断奶后的儿童,其食物中包含更多的植物作为辅食。本研究,印证了我国历史文献中有关儿童喂养模式的最早记载(唐代孙思邈的医书《千金方》),也为系统探索我国古代儿童的断奶模式和喂养方式提供了很好的范例。     

Variation in carbon and nitrogen isotopic ratios of fin and muscle tissues of Longnose Gar (Lepisosteus osseus) and Smallmouth Buffalo (Ictiobus bubalus)

Fin clips have been proposed as a non-lethal and non-invasive alternative to dorsal muscle samples in stable isotope analysis. However, potential differences in elemental composition and turnover rates can bias inferences when different tissues are combined. Here, we tested the average difference and correlation of the isotopic signature of δ¹³C and δ¹⁵N between muscle and fin samples in two arge-bodied fishes: Longnose Gar (Lepisosteus osseus) and Smallmouth Buffalo (Ictiobus bubalus). We found that δ¹⁵N signatures of muscle and fin tissues were strongly and positively correlated for both species, although the muscle tissue for Smallmouth Buffalo was slightly more enriched in δ15N. δ¹³C signatures of both tissues were significatively different and not strongly correlated for Longnose Gar, but similar and strongly correlated for Smallmouth Buffalo. Our results suggest that fin and muscle tissue can be combined for analyses of δ¹⁵N, but correction for higher enrichment of muscle tissue may be necessary for Smallmouth Buffalo. Conversely, combining fin and muscle tissue for analysis of δ¹³C requires more caution due to their weaker correlation and dependence of species identity.     

Dual‐tracer‐based isotope turnover rates in a highly invasive mysid Limnomysis benedeni from Lake Constance

Understanding the ecological patterns of invasive species and their habitats require an understanding of the species’ foraging ecology. Stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope values provide useful information into the study of animal ecology and evolution, since the isotope ratios of consumers reflect consumer's dietary patterns. Nevertheless, the lack of species‐ and element‐specific laboratory‐derived turnover rates could limit their application. Using a laboratory‐based dual stable isotope tracer approach (Na¹⁵NO₃ and NaH¹³CO₃), we evaluated the δ¹⁵N and δ¹³C isotope turnover rates in full‐grown adult invasive Limnomysis benedeni from Lake Constance. We provide δ¹⁵N and δ¹³C turnover rates based on nonlinear least‐squares regression and posterior linear regression models. Model precisions and fit were evaluated using Akaike's information criterion. Within a couple of days, the δ¹⁵N and δ¹³C of mysids began to change. Nevertheless, after about 14 days, L. benedeni did not reach equilibrium with their new isotope values. Since the experiment was conducted on adult subjects, it is evident that turnover was mainly influenced by metabolism (in contrast to growth). Unlike traditional dietary shifts, our laboratory‐based dual stable isotope tracer approach does not shift the experimental organisms into a new diet and avoids dietary effects on isotope values. Results confirm the application of isotopic tracers to label mysid subpopulations and could be used to reflect assimilation and turnover from the labeled dietary sources. Field‐based stable isotope studies often use isotopic mixing models commonly assuming diet‐tissue steady state. Unfortunately, in cases where the isotopic composition of the animal is not in equilibrium with its diet, this can lead to highly misleading conclusions. Thus, our laboratory‐based isotopic incorporation rates assist interpretation of the isotopic values from the field and provide a foundation for future research into using isotopic tracers to investigate invasion ecology.     

Fin tissues as surrogates of white muscle when assessing carbon and nitrogen stable isotope levels for Arctic and brook char

Arctic char (Salvelinus alpinus) are a fish species ubiquitous to the fresh waters of Arctic region and brook char (Salvelinus fontinalis) are similarly common across the sub-Arctic region of eastern Canada. Populations can be small in numbers, especially farther north thus it is important to develop non-lethal methods of sampling these fish to minimize the invasiveness and impact of scientific research. We examined the stable isotopes of nitrogen and carbon in white muscle, caudal fin, and adipose fin tissues of Arctic char and brook char (S. fontinalis) from northern Quebec and Labrador, Canada. Our results revealed several broad conclusions. First, differences among muscle, caudal fin, and adipose fin tissues were ~1?‰ for freshwater Arctic and brook char. Second, the two species within the same drainage had similar stable isotope levels and tissue differences. Third, anadromous Arctic char show similar, non-significant differences among these tissues for δ¹⁵N, but muscle δ¹³C was highly enriched. Fourth, the stable isotope levels and tissue differences were the same for anadromous Arctic char from two watersheds where char use distinctly different ocean environments. Overall, it appears that caudal fin tissue in particular is a useful surrogate for white muscle δ¹³C and δ¹⁵N levels for Arctic and brook char in this region and thus, a non-lethal collection of a small sample of caudal fin tissue will provide an accurate measure of white muscle isotope levels.     

Effects of food quality on tissue-specific isotope ratios in the mussel <Emphasis Type="Italic">Perna perna</Emphasis>

Investigations into trophic ecology and aquatic food web resolution are increasingly accomplished through stable isotope analysis. The incorporation of dietary and metabolic changes over time results in variations in isotope signatures and turnover rates of producers and consumers at tissue, individual, population and species levels. Consequently, the elucidation of trophic relationships in aquatic systems depends on establishing standard isotope values and tissue turnover rates for the level in question. This study investigated the effect of diet and food quality on isotopic signatures of four mussel tissues: adductor muscle, gonad, gill and mantle tissue from the brown mussel Perna perna. In the laboratory, mussels were fed one of the two isotopically distinct diets for 3 months. Although not all results were significant, overall δ¹³C ratios in adductor, mantle and gill tissues gradually approached food source signatures in both diets. PERMANOVA analyses revealed significant changes over time in tissue δ¹³C (mantle and gill) with both diets and in δ¹⁵N (all tissues) and C:N ratios (mantle and gill) for one diet only. The percentage of replaced carbon isotopes were calculated for the 3 month period and differed among tissues and between diets. The tissue with the highest and lowest amount of replaced isotopes over 81 days were mantle tissue on the kelp diet (33.89%) and adductor tissue on the fish food diet (4.14%), respectively. Percentages could not be calculated for any tissue in either diet for δ¹⁵N due to the lack of significant change in tissue nitrogen. Fractionation patterns in tissues for both diets can be linked to nutritional stress, suggesting that consumer isotopic signatures are strongly dependent on food quality, which can significantly affect the degree of isotopic enrichment within a trophic level.     

Tissue-specific turnover rates of the nitrogen stable isotope as functions of time and growth in a cyprinid fish

Ecological applications of stable isotope data require knowledge on the isotopic turnover rate of tissues, usually described as the isotopic half-life in days (T _0.5) or the change in mass (G _0.5). Ecological studies increasingly analyse tissues collected non-destructively, such as fish fin and scales, but there is limited knowledge on their turnover rates. Determining turnover rates in situ is challenging, with ex situ approaches preferred. Correspondingly, T _0.5 and G _0.5 of the nitrogen stable isotope (δ¹⁵N) were determined for juvenile barbel Barbus barbus (5.5 ± 0.6 g starting weight) using a diet-switch experiment. δ¹⁵N data from muscle, fin and scales were taken during a 125 day post diet-switch period. Whilst isotopic equilibrium was not reached in the 125 days, the δ¹⁵N values did approach those of the new diet. The fastest turnover rates were in more metabolically active tissues, from muscle (highest) to scales (lowest). Turnover rates were relatively slow; T _0.5 was 84 (muscle) to 145 (scale) days; G _0.5 was 1.39 × body mass (muscle) to 2.0 × body mass (scales), with this potentially relating to the slow growth of the experimental fish. These turnover estimates across the different tissues emphasise the importance of estimating half-lives for focal taxa at species and tissue levels for ecological studies.     

Stable isotope fractionation between maternal and embryo tissues in the Bonnethead shark (<Emphasis Type="Italic">Sphyrna tiburo</Emphasis>)

Evaluating tissue fractionation between mothers and their offspring is fundamental for informing our interpretation of stable isotope values in young individuals and can provide insight into the dynamics of maternal provisioning. The objectives of this study were to investigate the isotopic relationships between maternal reproductive (i.e., yolk, yolk-sac placenta) and somatic tissues (i.e., muscle and liver) relative to embryos in the Bonnethead Shark Sphyrna tiburo, to evaluate the fractionation of stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopes between these tissues. Additionally, we examined intra-uterine variability in the isotopic relationships to ascertain whether this species may exhibit variable nutrient allocation. Embryos showed similar magnitudes of enrichment in ¹³C (i.e., Δδ¹³C, difference between adult and embryo) relative to adult tissues (Δδ¹³C?=?~1.0‰). However, embryos were depleted in ¹⁵N relative to adult muscle tissues (Δδ¹⁵N?=??1.0‰), a finding that contrasts Δδ¹⁵N values reported for other placentotrophic sharks. Embryo-muscle Δδ¹⁵N was correlated with length, supporting the contention that the magnitude of enrichment between embryonic and maternal tissues results from the shift from yolk to placental feeding. Embryo δ¹⁵N and Δδ¹⁵N values showed significant intra-uterine variability; a result not observed for δ¹³C and Δδ¹³C values. The contrasting patterns in fractionation among placentotrophic sharks highlight the importance of evaluating these relationships across elasmobranch taxa with consideration for different tissues, reproductive strategies and stages of gestation. The divergent findings support future evaluation of stable isotope relationships between mothers and offspring for purposes of estimating inherent isotopic variability and how this variability may inform physiological and dietary mechanisms.     

Factors influencing the turnover and net isotopic discrimination of hydrogen isotopes in proteinaceous tissue: experimental results using Japanese quail

Stable hydrogen isotopes (δ(2)H) are commonly used in studies of animal movement. Tissue that is metabolically inactive after growth (e.g., feathers) provides spatial or dietary information that reflects only the period of tissue growth, whereas tissues that are metabolically active (e.g., red blood cells) provide a moving window of forensic information. However, using δ(2)H for studies of animal movement relies on the assumption that tissue δ(2)H values reflect dietary δ(2)H values, plus or minus a net diet-tissue discrimination value, and that the turnover rate is known for metabolically active tissue. The metabolic rate of an animal may influence both diet-tissue discrimination values and isotopic tissue turnover rate, but this hypothesis has not been tested experimentally. To examine the metabolic hypothesis, an experimental group of 12 male and 15 female captive Japanese quail (Coturnix japonica) was housed at 8.9°C for 90 d to elevate their metabolic rates (mL CO(2) min(-1)), and a control group of 12 male and 13 female quail was housed at room temperature during the same period. For both experimental and control birds, diet-tissue discrimination values were estimated for red blood cells and feathers. To determine turnover rate, experimental and control birds were switched from a (2)H-enriched diet to a (2)H-depleted diet, with red blood cells sampled before and after diet switch. Metabolic rate did not influence red blood cell hydrogen isotope turnover rate (η(2)(p) = 0.24)) or diet-feather isotope discrimination values (η(2)(p) = 0.86). Diet-feather hydrogen isotopic discrimination had a significant sex plus treatment interaction effect; female feathers were depleted in (2)H relative to food regardless of treatment, whereas male feathers were enriched in (2)H. The effect of sex suggested that experimental studies should examine whether coeval males and females differ in blood δ(2)H levels during certain periods of the annual cycle.     

Effects of elemental composition on the incorporation of dietary nitrogen and carbon isotopic signatures in an omnivorous songbird

The use of stable isotopes to infer diet requires quantifying the relationship between diet and tissues and, in particular, knowing of how quickly isotopes turnover in different tissues and how isotopic concentrations of different food components change (discriminate) when incorporated into consumer tissues. We used feeding trials with wild-caught yellow-rumped warblers (Dendroica coronata) to determine delta15N and delta13C turnover rates for blood, delta15N and delta13C diet-tissue discrimination factors, and diet-tissue relationships for blood and feathers. After 3 weeks on a common diet, 36 warblers were assigned to one of four diets differing in the relative proportion of fruit and insects. Plasma half-life estimates ranged from 0.4 to 0.7 days for delta13C and from 0.5 to 1.7 days for delta15N . Half-life did not differ among diets. Whole blood half-life for delta13C ranged from 3.9 to 6.1 days. Yellow-rumped warbler tissues were enriched relative to diet by 1.7-3.6% for nitrogen isotopes and by -1.2 to 4.3% for carbon isotopes, depending on tissue and diet. Consistent with previous studies, feathers were the most enriched and whole blood and plasma were the least enriched or, in the case of carbon, slightly depleted relative to diet. In general, tissues were more enriched relative to diet for birds on diets with high percentages of insects. For all tissues, carbon and nitrogen isotope discrimination factors increased with carbon and nitrogen concentrations of diets. The isotopic signature of plasma increased linearly with the sum of the isotopic signature of the diet and the discrimination factor. Because the isotopic signature of tissues depends on both elemental concentration and isotopic signature of the diet, attempts to reconstruct diet from stable isotope signatures require use of mixing models that incorporate elemental concentration.