Expression divergence, primarily defined as the proportion of differentially expressed genes, is one of the key parameters in assessing the evolutionary dynamics of diverging species. Most contributions toward expression differences between species and sexes come from testis tissue, which is the repertoire of rapidly diverging genes that can have a direct impact on speciation. To address the evolutionary dynamics among recently diverged Drosophila species, we analyzed testis transcriptomes of two members of nasuta subgroup of the immigrans species group: Drosophila nasuta nasuta and Drosophila nasuta albomicans. Using RNA-Seq and de novo assembly approach, we found that 96% of the transcriptome exhibited a conserved pattern of gene expression, typical of the recently diverged species'. The 4% of the characterized transcriptomes showing expression divergence had no influence of coding sequence variations. Four of the orthologous testicular genes are under relaxed positive selection, and the remaining 98% (n = 597) exhibit strong purifying selection irrespective of their expression patterns. Overall, our analyses suggest that the recent divergence of this closely related species pair has had a minimal impact on coding sequences and their expression, thereby providing useful insights into early stages of species divergence.

表达差异（主要定义为差异表达基因的比例）是评估差异物种进化动力学的关键参数之一。对物种和性别之间表达差异的大多数贡献来自睾丸组织，睾丸组织是迅速分化的基因的一个组成部分，可直接影响物种形成。为了解决近来不同的果蝇物种之间的进化动力学，我们分析了两个移民物种物种nasuta亚组成员的睾丸转录组：Drosophila nasuta nasuta和Drosophila nasuta albomicans。使用RNA-Seq和从头开始组装方法，我们发现96％的转录组表现出保守的基因表达模式，这是最近分化物种的典型特征。显示表达差异的4％的特征转录组不影响编码序列的变化。直系同源睾丸基因中的四个处于宽松的阳性选择下，其余98％（n = 597）不论其表达方式如何，均表现出较强的纯化选择。总体而言，我们的分析表明，这种紧密相关的物种对的近期发散对编码序列及其表达的影响极小，从而为了解物种发散的早期阶段提供了有用的见识。