Data from: Sex-specific phenotypes and metabolism-related gene expression in juvenile sticklebacks

To fully understand the evolution of sexual dimorphism, it is necessary to study how genetic and developmental systems function to generate sex-specific phenotype as well as sex-specific selection. Males and females show different patterns of energy storage and mitochondrial metabolism from early stages of life, and this may underlie sex-specific developmental pathway to shape both juvenile and adult phenotype. Here, we examined sex-specific relationships between juvenile morphology and behavior, and transcriptional profiles of 4 candidate genes related to mitochondrial function in the 3-spined stickleback. This study provides, for the first time to our knowledge, evidence for sex differences in melanin pigmentation and antipredator behavior as well as the expression of mitochondria-related genes in juvenile sticklebacks. Males were paler and bolder, and overexpressed genes involved in mitochondrial respiration and antioxidant enzymes compared to females. Relationships between phenotypic traits and gene expression were also sex-specific. In general, females showed stronger positive correlations between body size or pigmentation and the expression of genes involved in mitochondrial biogenesis and activity. In both sexes, more fearful individuals overexpressed those genes. Our results suggest that mitochondrial function may either facilitate or constrain sex-specific responses to selection on dimorphic phenotype, possibly generating intralocus sexual conflict on the transcriptional regulation of mito-nuclear genes during ontogeny. This study highlights that mitochondrial regulation plays an important role in the process of phenotypic differentiation between the 2 sexes from early stages of life before apparent sexual dimorphism appears.

为全面阐明性二态性（sexual dimorphism）的演化机制，有必要探究遗传与发育系统如何调控性别特异性表型的产生，以及性别特异性选择的作用模式。雄性与雌性自生命早期便在能量储存与线粒体代谢模式上存在差异，这或为塑造幼体与成体表型的性别特异性发育通路奠定基础。
本研究以三刺鱼（3-spined stickleback）为研究对象，分析了幼体形态与行为之间的性别特异性关联，并检测了4个与线粒体功能相关的候选基因的转录组谱。据我们所知，本研究首次在幼体三刺鱼中证实了黑色素沉着、反捕食行为以及线粒体相关基因表达存在性别差异：雄性体色更浅、胆子更大，且相较于雌性，其线粒体呼吸与抗氧化酶相关基因的表达量更高。
表型性状与基因表达之间的关联同样存在性别特异性。总体而言，雌性个体的体型或色素沉着与线粒体生物发生及活性相关基因的表达量呈更强的正相关；而在两种性别中，表现更趋恐惧的个体，上述线粒体相关基因的表达量均更高。
研究结果表明，线粒体功能或可促进或制约性二态表型相关的性别特异性选择响应，可能在个体发育（ontogeny）过程中，对线粒体-核基因的转录调控产生基因座内性冲突（intralocus sexual conflict）。
本研究凸显了线粒体调控在性二态性尚未显现的生命早期阶段，推动两性表型分化过程中的重要作用。