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26During cold acclimation fruit flies switch their feeding from yeast to plant food, however there 27 are no robust markers to monitor it in the wild. Drosophila melanogaster is a sterol auxotroph 28 and relies on dietary sterols to produce lipid membranes, lipoproteins and molting hormones. 29 We employed shotgun lipidomics to quantify eight major food sterols in total extracts of heads, 30 female and male genital tracts of adult flies. We found that their sterol composition is dynamic 31 and reflective of flies diet in an organ-specific manner. Season-dependent changes observed in 32 the organs of wild-living flies suggested that the molar ratio between yeast (ergosterol, 33 zymosterol) and plant (sitosterol, stigmasterol) sterols is a quantifiable, generic and 34 unequivocal marker of their feeding behavior, including cold acclimation. It provides 35 technically simpler and more contrast readout compared to the full lipidome analysis and is 36 suitable for ecological and environmental population-based studies. 37 38 39 3 40 Introduction 41 42 Drosophila melanogaster (Dm) is an established model to study dietary and environmental 43 impact on lipid homeostasis and development [1]. Although in the wild Dm is believed to feed 44 on yeasts grown on rotten fruits and plants, it can also develop on a variety of foods, including 45 an artificially delipidated diet supplemented with sterols [2]. Dm lacks Δ-6 and Δ-5 desaturases 46 [3] and can only produce short-to medium-chain fatty acids comprising not more than one 47 double bond [4]. However, Dm also makes use of dietary lipids with polyunsaturated fatty acid 48 moieties (e.g. unsaturated triacylglycerols from plant oil) and incorporate them into its own 49 lipids [5,6]. Manipulating the composition of laboratory diets helps to produce larvae and adult 50 flies with a varying degree of unsaturation of their glycero-and glycerophospholipids and study 51 their impact on metabolism and physiology. However, changes in lipids unsaturation span 52 many lipid classes in a tissue-dependent manner and therefore a snapshot of the full-lipidome 53 profile could hardly serve as a robust marker of shifting dietary preference. 54 Like other arthropods, Drosophila is a sterol auxotroph: it exclusively relies on dietary 55 sterols to build biological membranes, lipoproteins, and to produce molting hormones [7]. Each 56 common dietary component supplies flies with unique sterols: a commonly used yeast food 57 (YF) is enriched in ergosterol (Erg); plant food (PF) contains phytosterols e.g. sitosterol (Sit), 58 campesterol (Cam) or stigmasterol (Sti), while animal components supply cholesterol (Cho) 59 (Figure 1). We hypothesized that, in comparison to the full lipidome composition, sterol 60 composition could be a more specific dietary marker supporting ecological and nutritional 61 studies also in wild-living animals. 62Our recent study showed that switching from yeast to plant diet increased flies survival 63 at low temperatures by preserving the fluidity of their biological...

Raspberry (Rubus idaeus L.) is an important fruit crop (Graham et al., 2004) and cultivated in most areas in the world (Strik, 2007). Raspberry fruits are grown for fresh fruit market or commercial processing including products like juice, dried or frozen fruit and puree and its leaves are known for an astringent flavour in herbal teas (Hanke & Flachowsky, 2017). The main producing world re

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