Department of Zoology, Institute of Biosciences, University of São Paulo, R. Matão, Tv. 14, 101, 05508-090 São Paulo, Brazil.
Departamento de Biologia Animal, Centro de Ciências Biológicas e da Saúde, Universidade Federal de Viçosa, Av. P.H. Rolfs, s/n, 36570-900 Viçosa, Brazil.
Proc Biol Sci. 2023 Aug 9;290(2004):20230543. doi: 10.1098/rspb.2023.0543. Epub 2023 Aug 2.
Medusozoa (Cnidaria) are characterized by diverse life cycles, with different semaphoronts (medusa, medusoid, fixed gonophore, polyp) representing the sexual phase and carrying the gametes. Although egg size is often considered a proxy to understand reproductive and developmental traits of medusozoans, understanding of the processes influencing egg size variation in the group under an evolutionary context is still limited. We carried out a comprehensive review of the variation of egg size in Medusozoa to test whether this variation is related to biological/sexual or environmental traits. Egg size presents a strong phylogenetic signal ( = 0.79, = 0.67), explaining why closely related species with different reproductive strategies and different individual sizes have similar egg sizes. However, variation in egg size is influenced by the number of eggs, depth and temperature, with larger eggs frequently present in species with few eggs (1-15), in deep-sea species and in cold-water species. Conversely, the production of small eggs among cold-water species of Staurozoa might be associated with the development of a small benthic larvae in this group. Our study reinforces that egg sizes respond to reproductive and environmental traits, although egg size is highly conserved within medusa classes.
水螅虫动物门（刺胞动物门）的生命周期多种多样，不同的幼体（水螅体、水螅型幼体、固着生殖体、水螅型幼体）代表有性阶段并携带配子。尽管卵大小通常被认为是了解水螅动物门生殖和发育特征的一个指标，但对于该门中影响卵大小变异的进化过程的理解仍然有限。我们对水螅动物门卵大小的变异进行了全面综述，以检验这种变异是否与生物/性或环境特征有关。卵大小呈现出强烈的系统发育信号（ = 0.79， = 0.67），这解释了为什么具有不同生殖策略和不同个体大小的密切相关的物种具有相似的卵大小。然而，卵大小的变异受到产卵数量、深度和温度的影响，在产卵数量较少（1-15）、深海物种和冷水物种中，通常存在较大的卵。相反，冷水环境下的Staurozoa 物种产生小卵可能与该群体中小型底栖幼虫的发育有关。我们的研究强化了卵大小对生殖和环境特征的响应，尽管在水螅类中卵大小高度保守。
