The Whitney Laboratory for Marine Bioscience, University of Florida, St. Augustine, FL 32080.
Department of Biology, University of Florida, Gainesville, FL 32611.
Proc Natl Acad Sci U S A. 2022 May 3;119(18):e2122052119. doi: 10.1073/pnas.2122052119. Epub 2022 Apr 27.
A substantial body of literature reports that ctenophores exhibit an apparently unique life history characterized by biphasic sexual reproduction, the first phase of which is called larval reproduction or dissogeny. Whether this strategy is plastically deployed or a typical part of these species’ life history was unknown. In contrast to previous reports, we show that the ctenophore Mnemiopsis leidyi does not have separate phases of early and adult reproduction, regardless of the morphological transition to what has been considered the adult form. Rather, these ctenophores begin to reproduce at a small body size and spawn continuously from this point onward under adequate environmental conditions. They do not display a gap in productivity for metamorphosis or other physiological transition at a certain body size. Furthermore, nutritional and environmental constraints on fecundity are similar in both small and large animals. Our results provide critical parameters for understanding resource partitioning between growth and reproduction in this taxon, with implications for management of this species in its invaded range. Finally, we report an observation of similarly small-size spawning in a beroid ctenophore, which is morphologically, ecologically, and phylogenetically distinct from other ctenophores reported to spawn at small sizes. We conclude that spawning at small body size should be considered as the default, on-time developmental trajectory rather than as precocious, stress-induced, or otherwise unusual for ctenophores. The ancestral ctenophore was likely a direct developer, consistent with the hypothesis that multiphasic life cycles were introduced after the divergence of the ctenophore lineage.
大量文献报道称，栉水母表现出一种明显独特的生活史，具有两阶段的有性繁殖，第一阶段称为幼虫繁殖或异态生殖。这种策略是可塑性的还是这些物种生活史的典型部分尚不清楚。与之前的报道相反，我们表明，无论形态转变为被认为是成年形式，栉水母 Mnemiopsis leidyi 都没有早期和成年繁殖的独立阶段。相反，这些栉水母在体型较小时就开始繁殖，并在足够的环境条件下从此时起持续产卵。它们在一定体型下不会出现生产力的差距，以进行变态或其他生理转变。此外，营养和环境对繁殖力的限制在大小动物中相似。我们的结果为理解该分类群中生长和繁殖之间的资源分配提供了关键参数，对管理该物种在入侵地区具有重要意义。最后，我们报告了一个关于小型有栉水母的产卵观察结果，该有栉水母在形态、生态和系统发育上与其他报告的小型产卵栉水母明显不同。我们得出结论，在小体型产卵应被视为默认的、适时的发育轨迹，而不是早熟、应激诱导的或其他不寻常的栉水母特征。原始栉水母可能是直接发育的，这与多阶段生命周期是在栉水母谱系分化后引入的假设一致。
