A population genomic scan in Chorthippus grasshoppers unveils previously unknown phenotypic divergence

Understanding the genetics of speciation and the processes that drive it is a central goal of evolutionary biology. Grasshoppers of the Chorthippus species group differ strongly in calling song (and corresponding female preferences) but are exceedingly similar in other characteristics such as morphology. Here, we performed a population genomic scan on three Chorthippus species (Chorthippus biguttulus, C. mollis and C. brunneus) to gain insight into the genes and processes involved in divergence and speciation in this group. Using an RNA-seq approach, we examined functional variation between the species by calling SNPs for each of the three species pairs and using FST-based approaches to identify outliers. We found approximately 1% of SNPs in each comparison to be outliers. Between 37% and 40% of these outliers were nonsynonymous SNPs (as opposed to a global level of 17%) indicating that we recovered loci under selection. Among the outliers were several genes that may be involved in song production and hearing as well as genes involved in other traits such as food preferences and metabolism. Differences in food preferences between species were confirmed with a behavioural experiment. This indicates that multiple phenotypic differences implicating multiple evolutionary processes (sexual selection and natural selection) are present between the species.

解析物种形成的遗传学机制及其驱动过程，是进化生物学的核心研究目标之一。雏蝗属（Chorthippus）物种类群的鸣唱声（及其对应的雌性择偶偏好）存在显著差异，但在形态学等其他特征上却极为相似。本研究针对三个雏蝗属物种（Chorthippus biguttulus、C. mollis及C. brunneus）开展种群基因组扫描，以期深入解析该类群物种分化与形成过程中涉及的基因及分子机制。本研究采用RNA测序（RNA-seq）技术，通过对三个物种类对分别调用单核苷酸多态性（Single Nucleotide Polymorphism, SNP）位点，并运用基于固定指数（FST）的方法筛选离群位点，以此分析物种间的功能变异。研究发现，每组物种对的比较中约有1%的SNP位点为离群位点。其中37%至40%的离群位点为非同义SNP（全局占比仅为17%），表明本研究成功筛选到了受选择作用的基因座。在筛选得到的离群位点中，存在若干可能与鸣唱产生、听觉感知相关的基因，同时也包含与食性偏好、代谢等其他性状相关的基因。物种间的食性偏好差异已通过行为学实验得到验证。这表明，该类群物种间存在多重表型差异，且这些差异涉及性选择与自然选择等多种进化过程。