Many plant and fungal species use volatile organic compounds (VOCs) as chemical signals to convey information about the location or quality of their fruits or fruiting bodies to animal dispersers. Identifying the environmental factors and biotic interactions that shape fruit selection by animals is key to understanding the evolutionary processes that underpin chemical signaling. Using four Elaphomyces truffle species, we explored the role of fruiting depth, VOC emissions, and protein content in selection by five rodent species. We used stable isotope analysis of nitrogen (δ15 N) in truffles to estimate fruiting depth, proton-transfer-reaction mass spectrometry to determine volatile emission composition, and nitrogen concentrations to calculate digestible protein of truffles. We coupled field surveys of truffle availability with truffle spore loads in rodent scat to determine selection by rodents. Despite presumably easier access to the shallow fruiting species, E. americanus (0.5 cm depth) and E. verruculosus (2.5 cm depth), most rodents selected for truffles fruiting deeper in the soil, E. macrosporus (4.1 cm depth) and E. bartlettii (5.0 cm depth). The deeper fruiting species had distinct VOC profiles and produced significantly higher quantities of odiferous compounds. Myodes gapperi (southern red-backed vole), a fungal specialist, also selected for truffles with high levels of digestible protein, E. verruculosus and E. macrosporus. Our results highlight the importance of chemical signals in truffle selection by rodents and suggest that VOCs are under strong selective pressures relative to protein rewards. Strong chemical signals likely allow detection of truffles deep within the soil and reduce foraging effort by rodents. For rodents that depend on fungi as a major food source, protein content may also be important in selecting truffles.

中文翻译：

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来自下方的信号：啮齿动物选择更深的结实松露，具有更强的挥发性排放

许多植物和真菌物种使用挥发性有机化合物 (VOC) 作为化学信号，向动物传播者传达有关其果实或子实体的位置或质量的信息。确定影响动物水果选择的环境因素和生物相互作用是理解支持化学信号的进化过程的关键。我们使用四种松露松露菌物种，探讨了果实深度、VOC 排放和蛋白质含量在五种啮齿动物物种选择中的作用。我们使用松露中氮 (δ15 N) 的稳定同位素分析来估计结果深度，使用质子转移反应质谱法确定挥发性排放成分，并使用氮浓度来计算松露的可消化蛋白质。我们将松露可用性的实地调查与啮齿动物粪便中的松露孢子负荷相结合，以确定啮齿动物的选择。尽管可能更容易接触到浅层结果物种 E. americanus（0.5 cm 深）和 E. verruculosus（2.5 cm 深），但大多数啮齿动物选择了在土壤中结实更深的松露，E. macrosporus（4.1 cm 深）和 E. bartlettii（5.0 厘米深）。较深的果实种类具有明显的 VOC 特征，并产生显着更多的气味化合物。Myodes gapperi（南方红背田鼠）是一种真菌专家，也被选用于具有高水平可消化蛋白质、E. verruculosus 和 E. macrosporus 的松露。我们的结果强调了化学信号在啮齿动物选择松露中的重要性，并表明 VOC 相对于蛋白质奖励处于强大的选择压力之下。强化学信号可能允许检测到土壤深处的松露并减少啮齿动物的觅食工作。对于依赖真菌作为主要食物来源的啮齿动物，蛋白质含量在选择松露时也很重要。