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 four candidate genes related to mitochondrial function in the three-spined stickleback. This study provides, for the first time to our knowledge, evidence for sex differences in melanin pigmentation and anti-predator 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 intra-locus 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 two 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，亟需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方式。雌雄个体自生命早期便在能量储存模式与线粒体代谢特征上存在显著差异，这可能是驱动性别特异性发育通路、进而塑造幼体与成体表型的核心基础。本研究以三刺鱼（three-spined stickleback）为实验对象，分析了幼体形态与行为的性别特异性关联，以及4个与线粒体功能相关的候选基因的转录表达谱。据我们所知，本研究首次为幼体三刺鱼的黑色素沉着、反捕食行为以及线粒体相关基因表达存在性别差异提供了实证依据。相较于雌性个体，雄性体色更浅、胆量更大，且线粒体呼吸通路与抗氧化酶相关基因的表达量显著上调。表型性状与基因表达之间的关联同样呈现性别特异性。总体而言，雌性个体的体型或色素沉着程度与线粒体生物发生及活性相关基因的表达量之间呈现出更强的正相关关系。在雌雄个体中，避险行为更强的个体上述线粒体相关基因的表达量均更高。本研究结果表明，线粒体功能既可能促进也可能制约性二态表型相关选择的性别特异性响应，进而可能在个体发育过程中引发线粒体核基因（mito-nuclear genes）转录调控层面的基因座内性冲突。本研究凸显了线粒体调控在明显性二态性出现前，从生命早期阶段即参与两性表型分化过程中的关键作用。