Wood Rachel A, Droser Mary L
School of Geosciences, University of Edinburgh, James Hutton Road, Edinburgh, EH9 3FE, UK.
Department of Earth and Planetary Science, University of California, Riverside, California, 92521, USA.
Biol Rev Camb Philos Soc. 2025 Oct;100(5):2084-2098. doi: 10.1111/brv.70036. Epub 2025 May 15.
The evolution of reproductive style is a fundamental aspect of metazoan life history but has not been explored holistically through the Ediacaran-Cambrian rise of metazoans. Recent molecular clock analyses based on only unequivocal metazoan fossil calibrations suggest that Porifera were present by at least 590 million years ago (Ma), all major eumetazoan clades originated in the mid-late Ediacaran, and bilaterians were probably present by the late Ediacaran. An alternating pelagic larval (potentially for dispersal) and benthic adult life cycle appears to be an ancestral feature of metazoans. A compilation of inferred reproductive styles from the fossil record reveals that the low-competition, deep-water communities of the Ediacaran Avalon macrofossil assemblage (ca. 575 to 560 Ma) had current-borne sexually produced larval with both local (non-planktotrophic, with no feeding) and more widespread (planktotrophic, with feeding) dispersal followed by vegetative growth. By ca. 560 Ma, White Sea assemblage communities in shallow settings show dense aggregations, which were often dominated by single populations of episodic sexually produced larval spatfalls. Some taxa may show potential larval philopatry. By 550 Ma, with the rise of biomineralization and colonisation of shallow marine carbonate settings, the ability to encrust hard substrates, create multiple branches via budding, and rudimentary mutual attachment of inferred clones, first appear. The dominant apparent mode of reproduction throughout the Ediacaran was therefore via current-borne sexually produced larvae followed by asexual reproduction, via either budding, fragmentation or fission. In these communities where biotic interactions were limited, this enabled colonisation of newly available soft and hard substrates followed by rapid growth. Early Cambrian communities showed increased endemism, enhanced trophic interactions and widespread macropredation. By the early Cambrian Fortunian stage (ca. 535 Ma), gonochorism (separate sexes) may have been present in priapulid worms. During Cambrian Stage 2 (ca. 532 Ma), internal fertilisation probably appeared in molluscs but widespread planktotrophy did not appear until the latest Cambrian/early Ordovician. Mutual attachment of diverse skeletal taxa became more common, particularly within reefs. Evidence for egg brooding and parental care in arthropods had appeared by the early Stage 3 (ca. 518 Ma). While reproductive styles were independently acquired, this overall pattern suggests a shift both to higher fecundity and to higher quality offspring in some groups during the Ediacaran-Cambrian Radiation, driven by increasing biotic interactions, including the rise of macropredation.
生殖方式的演化是后生动物生活史的一个基本方面，但尚未通过埃迪卡拉纪-寒武纪后生动物的兴起进行全面探索。最近仅基于明确的后生动物化石校准的分子钟分析表明，海绵动物至少在5.9亿年前就已出现，所有主要的真后生动物类群都起源于埃迪卡拉纪中晚期，而两侧对称动物可能在埃迪卡拉纪晚期就已出现。交替的浮游幼虫（可能用于扩散）和底栖成体生命周期似乎是后生动物的一个祖先特征。根据化石记录推断的生殖方式汇编显示，埃迪卡拉纪阿瓦隆宏观化石组合（约5.75亿至5.6亿年前）的低竞争、深水群落具有由水流携带的有性生殖产生的幼虫，既有局部（非浮游性营养，不摄食）扩散，也有更广泛的（浮游性营养，摄食）扩散，随后是营养生长。到约5.6亿年前，浅水环境中的白海组合群落显示出密集的聚集，这些聚集通常由间歇性有性生殖产生的幼虫附着的单一群体主导。一些分类群可能显示出潜在的幼虫恋巢性。到5.5亿年前，随着生物矿化的兴起和浅海碳酸盐环境的定殖，覆盖坚硬基质、通过出芽形成多个分支以及推断克隆的基本相互附着的能力首次出现。因此，在整个埃迪卡拉纪，主要的明显生殖方式是通过水流携带的有性生殖产生的幼虫，随后是通过出芽、断裂或裂变进行无性生殖。在这些生物相互作用有限的群落中，这使得能够在新出现的软质和硬质基质上定殖，随后快速生长。早寒武世群落显示出特有性增加、营养相互作用增强和广泛的大型捕食现象。到早寒武世福廷阶（约5.35亿年前），雄性先熟现象（雌雄异体）可能已存在于鳃曳虫类蠕虫中。在寒武纪第2阶段（约5.32亿年前），体内受精可能已出现在软体动物中，但广泛的浮游性营养直到寒武纪晚期/奥陶纪早期才出现。不同骨骼类群的相互附着变得更加普遍，尤其是在珊瑚礁内部。节肢动物中卵育和亲代抚育的证据在第3阶段早期（约5.18亿年前）就已出现。虽然生殖方式是独立获得的，但这一总体模式表明，在埃迪卡拉纪-寒武纪辐射期间，由于生物相互作用的增加，包括大型捕食的兴起，一些类群在生殖方式上发生了转变，既转向了更高的繁殖力，也转向了更高质量的后代。
