Determination of limiting polyunsaturated fatty acids in Daphnia galeata using a new method to enrich food algae with single fatty acids
Determination of limiting polyunsaturated fatty acids in Daphnia galeata using a new method to enrich food algae with single fatty acids
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采用单一脂肪酸富集食用藻新方法测定帽状溞中的限制性多不饱和脂肪酸
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发表时间：
2002
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通讯作者：
E. Elert
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作者：
E. Elert
采用一种新的方法，以高重复性的游离脂肪酸为补充剂，研究了高不饱和脂肪酸（PUFAs）对以栅列藻（Scenedesmus）和汉氏隐盘藻（Stephanodiscus hantzschii）为食的盔状水蚤（Daphnia galeata）体细胞生长的影响。以藻细胞为转移载体，利用D.盔状花序。在标准化的生长实验中，幼D。galeata、S.通过补充PUFAs α-亚麻酸（α-LA，18：3 n-3）、二十碳五烯酸（EPA，20：5 n-3）和二十二碳六烯酸（DHA，22：6 n-3）而不是花生四烯酸（ARA，20：4 n-6）来改善肌肉，这说明PUFAs不应被视为单一资源。相应的脂肪酸模式的变化D。galeata表明EPA是S. Alcohus和D. galeata将DHA和C18-PUFAs转化为EPA。生长在S。补充EPA和ARA不能改善hantzschii，但补充a-LA可以改善，这表明a-LA是限制性PUFA，EPA不能转化为a-LA。这些结果表明，EPA的可用性决定了哪些PUFA限制生长。由于水蚤类具有将α-LA转化为EPA的能力，因此在EPA限制下，两种PUFA都是可替代资源，但由于EPA不能转化为α-LA，因此在α-LA限制下，两种PUFA都是不可替代资源。在水生食物网中，调节初级生产者和消费者之间能量转移的因素对于理解植物-草食动物界面的能量转移至关重要。多年来已经清楚的是，从初级生产到次级生产的碳转移效率的变化相当大。这种变化可以归因于食物质量的变化，但食物质量的决定因素可能具有不同的性质，如形态，消化阻力，毒性和营养不足。从营养的角度来看，并非所有的碳单位都是相等的。营养有限的藻类（在淡水系统中大多是磷有限的）被广泛认为是一种低质量的食物来源（Sterner和Schulz 1998）。然而，在C：P比为300时，水蚤的食物质量可能会受到除P以外的其他因素的限制（Sundbom和Vrede 1997）。除非矿物限制、毒素或藻类形态限制藻类生物量的利用，否则藻类碳的质量决定碳转移效率。低质量的碳可能是由于饮食中缺乏必要的生物化学物质，因为这些营养素不能合成或由消费者合成的量不足以维持生长。多不饱和脂肪酸（PUFAs，具有两个或更多双键的脂肪酸）是许多脊椎动物和无脊椎动物所必需的（Stanley-Samuelson等人，1988年），最近已阐明PUFAs在淡水浮游动物营养中的重要性（Gulati和DeMott，1997年）。RE1
A new method that allows the highly reproducible supplementation of free fatty acids to planktonic microalgae was used to investigate the role of particular highly unsaturated fatty acids (PUFAs) in somatic growth limitation of Daphnia galeata feeding on Scenedesmus obliquus or Stephanodiscus hantzschii. No evidence for biotransformation of the supplemented fatty acids into other fatty acids by the algae was found. Using the algal cell itself as a transfer vehicle, the supplemented fatty acids were incorporated by D. galeata. In standardized growth experiments with juvenile D. galeata, growth on S. obliquus was improved by supplementation with the PUFAs a-linolenic acid (a-LA, 18:3n-3), eicosapentaenoic acid (EPA, 20:5n-3), and docosahexaenoic acid (DHA, 22:6n-3), but not by arachidonic acid (ARA, 20:4n-6), which illustrates that PUFAs should not be regarded as a single resource. Corresponding changes in the fatty acid pattern of D. galeata indicated that EPA is the limiting PUFA during growth on S. obliquus and that D. galeata converts DHA and C18-PUFAs into EPA. Growth on S. hantzschii was not improved by supplementation with EPA and ARA but was with a-LA, which indicates that a-LA is the limiting PUFA and that EPA cannot be converted into a-LA. These results suggest that the availability of EPA determines which PUFA is limiting for growth. Because of the ability of the daphnids to convert a-LA into EPA, both PUFAs are substitutable resources under EPA limitation, but because EPA cannot be converted into a-LA, both PUFAs are nonsubstitutable resources under a-LA limitation. In aquatic food webs, the factors that regulate energy transfer between primary producers and consumers are crucial in understanding the transfer of energy across the plant‐ herbivore interface. It has been clear for many years that variation in the carbon transfer efficiency from primary to secondary production is quite large. This variation can be attributed to variation in food quality, but the determinants of food quality might be of a different nature, such as morphology, digestive resistance, toxicity, and nutritional inadequacy. From a nutritional point of view, not all units of carbon are equal. Nutrient-limited algae (in freshwater systems mostly P-limited) are widely accepted to be a food source of low quality (Sterner and Schulz 1998). However, at C : P ratios ,300, food quality for Daphnia might become constrained by factors others than P (Sundbom and Vrede 1997). Unless mineral limitation, toxins, or algal morphology constrain the utilization of algal biomass, the quality of algal carbon determines carbon transfer efficiency. Low quality of carbon can be due to a shortage of essential biochemicals in the diet, since such nutrients cannot be synthesized or are synthesized by a consumer in amounts inadequate to sustain growth. Polyunsaturated fatty acids (PUFAs, fatty acids with two or more double bonds) are essential for many vertebrates and invertebrates (Stanley-Samuelson et al. 1988), and the importance of PUFAs in freshwater zooplankton nutrition has recently been articulated (Gulati and DeMott 1997). Re1