Sexual-size dimorphism (SSD) is replete among animals, but while the selective pressures that drive the evolution of SSD have been well studied, the developmental mechanisms upon which these pressures act are poorly understood. Ours and others’ research has shown that SSD in D. melanogaster reflects elevated levels of nutritional plasticity in females versus males, such that SSD increases with dietary intake and body size, a phenomenon called sex-specific plasticity (SSP). Additional data indicate that while body size in both sexes responds to variation in protein level, only female body size is sensitive to variation in carbohydrate level. Here, we explore whether these difference in sensitivity at the morphological level are reflected by differences in how the insulin/IGF-signaling (IIS) and TOR-signaling pathways respond to changes in carbohydrates and proteins in females versus males, using a nutritional geometry approach. The IIS-regulated transcripts of 4E-BP and InR most strongly correlated with body size in females and males, respectively, but neither responded to carbohydrate level and so could not explain the sex-specific response to body size to dietary carbohydrate. Transcripts regulated by TOR-signaling did, however, respond to dietary carbohydrate in a sex-specific manner. In females, expression of dILP5 positively correlated with body size, while expression of dILP2,3 and 8, was elevated on diets with a low concentration of both carbohydrate and protein. In contrast, we detected lower levels of dILP2 and 5 protein in the brains of females fed on low concentration diets. We could not detect any effect of diet on dILP expression in males. Although females and males show sex-specific transcriptional responses to changes in protein and carbohydrate, the patterns of expression do not support a simple model of the regulation of body-size SSP by either insulin- or TOR-signaling. The data also indicate a complex relationship between carbohydrate and protein level, dILP expression and dILP peptide levels in the brain. In general, diet quality and sex both affect the transcriptional response to changes in diet quantity, and so should be considered in future studies that explore the effect of nutrition on body size.

中文翻译：

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果蝇胰岛素信号基因表达的性别特异性可塑性和营养几何结构


性别大小二态性（SSD）在动物中很常见，但是虽然驱动SSD进化的选择压力已经得到了充分的研究，但这些压力作用的发育机制却知之甚少。我们和其他人的研究表明，黑腹果蝇中的 SSD 反映了雌性相对于雄性的营养可塑性水平升高，因此 SSD 随着饮食摄入量和体型的增加而增加，这种现象称为性别特异性可塑性 (SSP)。其他数据表明，虽然两性的体型都会对蛋白质水平的变化做出反应，但只有女性的体型对碳水化合物水平的变化敏感。在这里，我们使用营养几何学方法探讨了形态水平上的敏感性差异是否通过胰岛素/IGF信号传导（IIS）和TOR信号传导通路对雌性与雄性碳水化合物和蛋白质变化的反应方式的差异来反映。 。 IIS 调节的 4E-BP 和 InR 转录物分别与女性和男性的体型密切相关，但两者都对碳水化合物水平没有反应，因此无法解释饮食碳水化合物对体型的性别特异性反应。然而，受 TOR 信号传导调节的转录物确实以性别特异性方式对膳食碳水化合物做出反应。在女性中，dILP5 的表达与体型呈正相关，而 dILP2、3 和 8 的表达在碳水化合物和蛋白质浓度较低的饮食中升高。相比之下，我们在低浓度饮食的雌性大脑中检测到较低水平的 dILP2 和 5 蛋白。我们无法检测到饮食对男性 dILP 表达的任何影响。 尽管雌性和雄性对蛋白质和碳水化合物的变化表现出性别特异性转录反应，但表达模式并不支持胰岛素或TOR信号传导调节体型SSP的简单模型。数据还表明大脑中碳水化合物和蛋白质水平、dILP 表达和 dILP 肽水平之间存在复杂的关系。一般来说，饮食质量和性别都会影响对饮食量变化的转录反应，因此在未来探索营养对体型影响的研究中应该考虑到这一点。