Assessing the evolutionary history of the class Synurophyceae (Heterokonta) using molecular, morphometric, and paleobiological approaches

Premise of the study: Heterokont algae of the class Synurophyceae, characterized by distinctive siliceous scales that cover the surface of the cell, are ecologically important in inland waters, yet their evolutionary history remains enigmatic. We explore phylogenetic relationships within this group of algae relative to geologic time, with a focus on evolution of siliceous components. Methods: We combined an expansive five-gene and time-calibrated molecular phylogeny of synurophyte algae with an extensive array of fossil specimens from the middle Eocene to infer evolutionary trends within the group. Key results: The group originated in the Jurassic approximately 157 million years ago (Ma), with the keystone genera Mallomonas and Synura diverging during the Early Cretaceous at 130 Ma. Mallomonas further splits into two major subclades, signaling the evolution of the V-rib believed to aid in the spacing and organization of scales on the cell covering. Synura also diverges into two primary ...

研究背景：以覆盖细胞表面的独特硅质鳞片为典型特征的不等鞭毛类（Heterokont）硅鞭藻纲（Synurophyceae）藻类，在内陆水域中具有重要生态地位，但其演化历史至今仍属未解之谜。本研究结合地质时间尺度，探究该类藻类的系统发育关系，重点关注硅质结构的演化过程。
研究方法：我们整合了覆盖范围广泛的5个基因的时间校准分子系统发育数据，结合中始新世的大量化石标本，以推断该类群的演化趋势。
主要结果：该类群起源于侏罗纪，距今约1.57亿年（Ma，百万年前）；核心属鱼鳞藻属（Mallomonas）与合尾藻属（Synura）于早白垩世的1.3亿年前发生分化。鱼鳞藻属进一步分化为两个主要亚支，这标志着V-rib（V形肋）的演化——该结构被认为有助于维持细胞覆盖层中鳞片的间距与排列秩序。合尾藻属同样分化为两个主要分支……