Resource polymorphism in European whitefish: Analysis of fatty acid profiles provides more detailed evidence than traditional methods alone

Resource polymorphism—whereby ancestral generalist populations give rise to several specialised morphs along a resource gradient—is common where species colonise newly formed ecosystems. This phenomenon is particularly well documented in freshwater fish populations inhabiting postglacial lakes formed at the end of the last ice age. However, knowledge on how such differential exploitation of resources across contrasting habitats might be reflected in the biochemical compositions of diverging populations is still limited, though such patterns might be expected. Here, we aimed to assess how fatty acids (FA)—an important biochemical component of animal tissues—diverged across a polymorphic complex of European whitefish (Coregonus lavaretus) and their closely related monomorphic specialist congener vendace (Coregonus albula) inhabiting a series of six subarctic lakes in northern Fennoscandia. We also explored patterns of FA composition in whitefish’s predators and invertebrate prey to assess how divergence in trophic ecology between whitefish morphs would relate to biochemical profiles of their key food web associates. Lastly, we assessed how information on trophic divergence provided by differential FA composition compared to evidence of resource polymorphism retrieved from more classical stomach content and stable isotopic (δ13C, δ15N) information. Examination of stomach contents provided high-resolution information on recently consumed prey, whereas stable isotopes indicated broad-scale patterns of benthic-pelagic resource use differentiation at different trophic levels. Linear discriminant analysis based on FA composition was substantially more successful in identifying whitefish morphs and their congener vendace as distinct groupings when compared to the other two methods. Three major FA (myristic acid, stearic acid, and eicosadienoic acid) proved particularly informative, both in delineating coregonid groups, and identifying patterns of pelagic-benthic feeding throughout the wider food web. Myristic acid (14:0) content and δ13C ratios in muscle tissue were positively correlated across fish taxa, and together provided the clearest segregation of fishes exploiting contrasting pelagic and benthic niches. In general, our findings highlight the potential of FA analysis for identifying resource polymorphism in animal populations where this phenomenon occurs, and suggest that this technique may provide greater resolution than more traditional methods typically used for this purpose.资源多态性（Resource polymorphism）指祖先广食性种群沿资源梯度分化为若干特化形态的现象，在物种拓殖新生生态系统的场景中颇为常见。该现象在末次冰期结束后形成的冰后湖栖息的淡水鱼类种群中已有充分记载。然而，尽管此类模式本应存在，但学界对于不同生境中的差异化资源利用如何在分化种群的生化组成中得到体现，相关认知仍较为有限。本研究旨在探究脂肪酸（Fatty Acids, FA）——动物组织的重要生化组分——在栖息于芬诺斯堪的亚北部6个亚北极湖泊的欧洲白鲑（Coregonus lavaretus）多态类群，以及其近缘的单型特化同属物种白北鲑（vendace, Coregonus albula）中的分化模式。本研究同时分析了白鲑的捕食者与无脊椎动物猎物的脂肪酸组成，以明确白鲑不同形态间的营养生态分化与其关键食物网伙伴的生化特征之间的关联。此外，本研究对比了基于差异化脂肪酸组成得到的营养分化信息，与通过经典胃含物分析、稳定同位素（δ¹³C、δ¹⁵N）数据获取的资源多态性证据。研究结果显示，胃含物检测可提供近期摄食猎物的高分辨率信息，而稳定同位素则能反映不同营养层级上底栖-浮游资源利用分化的宏观模式。相较其余两种方法，基于脂肪酸组成的线性判别分析（Linear Discriminant Analysis）可更为精准地将白鲑形态类群及其同属的白北鲑（vendace, Coregonus albula）识别为独立分组。肉豆蔻酸（myristic acid）、硬脂酸（stearic acid）与二十碳二烯酸（eicosadienoic acid）这三种主要脂肪酸具备较高的信息价值，既可用于区分白鲑属类群，也可用于解析整个食物网中的浮游-底栖摄食模式。鱼类类群肌肉组织中的肉豆蔻酸（14:0）含量与δ¹³C比值呈正相关，二者结合可最为清晰地将利用不同浮游与底栖生态位的鱼类区分开来。总体而言，本研究结果凸显了脂肪酸分析在鉴定存在资源多态性的动物种群时的应用潜力，并表明该技术相较此类研究中常用的传统方法，可提供更高的分辨率。