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，亟需解析遗传与发育系统如何调控性别特异性表型（sex-specific phenotype）的生成，以及性别特异性选择（sex-specific selection）的作用模式。雌雄个体自生命早期便在能量储存与线粒体代谢（mitochondrial metabolism）模式上存在差异，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。本研究以三棘刺鱼（3-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，并检测了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，本研究首次为幼体刺鱼的黑色素沉着（melanin pigmentation）、反捕食行为（antipredator behavior）以及线粒体相关基因（mitochondria-related genes）表达层面的性别差异提供了实验证据：相较于雌性个体，雄性体色更浅、行为更胆大，且线粒体呼吸（mitochondrial respiration）与抗氧化酶（antioxidant enzymes）相关基因的表达量显著更高。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，雌性个体的体型或黑色素沉着与线粒体生物发生（mitochondrial biogenesis）及活性相关基因的表达量之间呈现更强的正相关关系；而在雌雄个体中，反捕食行为更谨慎的个体，上述基因的表达量均更高。本研究结果表明，线粒体功能既可促进亦可限制二态性表型相关选择的性别特异性响应，这可能在个体发育（ontogeny）过程中，引发核-线粒体基因（mito-nuclear genes）转录调控层面的位点内性别冲突（intralocus sexual conflict）。本研究揭示，在明显的性二态性出现之前，线粒体调控在雌雄个体自生命早期开始的表型分化过程中发挥了关键作用。