Individual specialization is a common phenomenon throughout the animal kingdom. Many studies have identified intraspecific competition as one of the main drivers for individual feeding specialization. These studies have mainly considered the quantity of resources, commonly overlooking qualitative aspects of the diet. For example, highly unsaturated fatty acids of the ω‐3 class (ω‐3 HUFAs) are related to optimal health and growth in consumers. However, little is known on direct fitness consequences for consumers of natural populations that specialize on high‐quality resources, such as those rich in ω‐3 HUFAs. Despite being such an important qualitative aspect of the diet, it is still unknown whether natural populations show among‐individual variation in their choice on prey items that are either rich or poor in HUFAs, and how it affects individual performances. In this study, we investigated whether there is individual feeding specialization and whether it is related to fitness benefits, in a population of perch (Perca fluviatilis) in the Baltic Sea. The contribution of pelagic planktivorous fish to the diet varied from 17% to 61% among perch individuals, as depicted by stable isotope mixing models. This variation in diet was also qualitative, as the ω‐3 HUFA content differed among prey types. Specialization on the high‐quality resource pelagic planktivorous fish was associated with the proportions of ω‐3 HUFA in the individuals’ muscles and individuals among those with the highest proportions of ω‐3 HUFAs had the greatest relative gonad weight (gonadosomatic index, GSI), a proxy for reproductive investment. Thus, our results highlight the function of food quality for individual specialization and its potential to have direct fitness benefits, playing a major role in shaping ecological interactions.

中文翻译：

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富含脂肪酸的猎物的喂养专家的性腺重量更高：在波罗的海鲈中有回报吗？

个体专业化是整个动物界的普遍现象。许多研究已经将种内竞争确定为个体饲料专业化的主要驱动力之一。这些研究主要考虑了资源的数量，通常忽略了饮食的质量方面。例如，ω-3类的高度不饱和脂肪酸（ω-3HUFA）与消费者的最佳健康状况和成长有关。但是，对于专门研究高质量资源的自然人群（如富含ω-3HUFA的人群）的直接适应性后果知之甚少。尽管饮食具有如此重要的质量方面的规定，但尚不清楚自然种群是否会因HUFA丰富或贫乏的猎物而在选择上出现个体差异，以及它如何影响个人表演。在这项研究中，我们调查了鲈鱼种群中是否存在个体化的喂养专业化，以及它是否与健身益处有关（Perca fluviatilis）在波罗的海。如稳定同位素混合模型所描绘的，鲈鱼个体中上层浮游鱼类对饮食的贡献从17％到61％不等。饮食上的这种变化也是定性的，因为ω-3HUFA含量在猎物类型之间有所不同。高质量资源中上层浮游鱼类的专业化与ω-3HUFA在个体肌肉中的比例有关，而ω-3HUFA比例最高的个体中性腺相对权重最大（性腺体指数，GSI） ，代表生殖投资。因此，我们的结果强调了食品质量对个体专业化的作用及其潜在的直接健身益处，在影响生态相互作用方面起着重要作用。