海龙科鱼类以动物界中独一无二的雄性怀孕策略而备受关注，其进化历程一直是鱼类演化界中的旗帜性问题。育儿袋为海龙科分类的重要形态学性状，但在海马属中，豆丁海马这一独特类群特有的“内置型”育儿袋与海马属其他种类存在较大差异。目前豆丁海马的系统分类与演化等基础问题尚不明确，本项目拟通过全基因组层面的系统进化分析，并结合育儿袋结构特征与繁殖行为的关联，从分子、形态学和行为学等多角度对其分类地位进行重新梳理和构建，以揭示豆丁海马类群的进化地位、分歧时间、历史有效群体动态和扩散模式等系统演化特征。此外，本研究将进一步在全基因组层面深入解析豆丁海马系统发育中关键基因的突变特征，甄选育儿袋发育相关基因，并阐释其在物种演化过程中的作用机制。综上，本研究将为豆丁海马的系统分类问题提出新的见解，并论证育儿袋作为海龙科物种系统分类依据的适用性，相关结果也将为海龙科物种复杂性状演化等领域的研究提供不可或缺的科学证据。

The Syngnathidae are famous for their elegant shapes and unique reproductive behavior - male pregnancy. Pygmy seahorse species, one of the most special groups in the Syngnathidae, live on corals and matches their color and appearance. They differ morphologically from all other seahorse species with a brood pouch located inside the trunk, rather than on the tail. However, since the research on pygmy seahorses is still limited, the existing data are far from enough to confirm the taxonomy position of these species, and their phylogeny and evolutionary process are remaining unsolved. In this project, we will use the whole-genome resequencing data to conduct the phylogenomic study of pygmy seahorse, seahorse, and some pipefish species to reveal the evolutionary history of pygmy seahorse species. For pygmy seahorse, morphological analysis, especially the location and structure of brood pouch will be performed, and reproductive behaviors will be observed, and compared to that of seahorses. Therefore, molecular, morphological and behavioral data will be combined to investigate the systematic evolution of pygmy seahorse species. Then, genes associated with brood pouch will be discovered based on comparative genomics study and transcriptome data, and phylogenetic analysis of those genes will be conducted to association between brood pouch structure and species phylogeny. This study aims to provide sufficient evidence to confirm the taxonomy position of pygmy seahorse species, and speculate on their evolutionary history. Results in this project can also provide a good foundation for future studies about the evolutionary trend of complex characteristics in Syngnathidae.