Convergent evolution of barnacles and molluscs sheds lights in origin and diversification of calcareous shell and sessile lifestyle

The calcareous shell and sessile lifestyle are the representative phenotypes of many molluscs, which happen to be present in barnacles, a group of unique crustaceans. The origin of these phenotypes is unclear, but it may be embodied in the convergent genetics of such distant groups (interphylum). Herein, we perform comprehensive comparative genomics analysis in barnacles and molluscs, and reveal a genome-wide strong convergent molecular evolution between them, including coexpansion of biomineralisation and organic matrix genes for shell formation, and origination of lineage-specific orphan genes for settlement. Notably, the expanded biomineralisation gene encoding alkaline phosphatase evolves a novel, highly conserved motif that may trigger the origin of barnacle shell formation. Unlike molluscs, barnacles adopt novel organic matrices and cement proteins for shell formation and settlement, respectively, and their calcareous shells have potentially originated from the cuticle system of c...钙质外壳与固着生活方式是多数软体动物（Molluscs）的典型表型，而这一特征恰好存在于一类独特的甲壳动物——藤壶（barnacles）中。此类表型的起源尚不明确，但其成因或蕴藏于这类远缘类群（跨门）的趋同遗传学机制中。本研究对藤壶与软体动物开展全面的比较基因组学分析，揭示了二者间全基因组水平的显著趋同分子演化特征：包括参与外壳形成的生物矿化（biomineralisation）与有机基质基因的共扩张，以及固着相关的谱系特异性孤儿基因的起源。值得注意的是，编码碱性磷酸酶（alkaline phosphatase）的扩张生物矿化基因演化出了全新且高度保守的基序（motif），这一特征或可触发藤壶钙质外壳的起源。与软体动物不同，藤壶分别采用全新的有机基质与胶黏蛋白完成外壳形成与固着过程，其钙质外壳或起源于c……的表皮系统。