Lesoway Maryna P, Abouheif Ehab, Collin Rachel
McGill University, Montreal, QC, Canada.
Int J Dev Biol. 2014;58(6-8):601-11. doi: 10.1387/ijdb.140136rc.
Adelphophagy occurs when encapsulated embryos complete development by feeding on their developing siblings, which are known as nutritive embryos. Nutritive embryos are found in a variety of animal groups, and are especially common in some groups of marine invertebrates. Although they have evolved numerous times independently in the calyptraeid gastropods, adelphophagic development with nutritive embryos has not been described in detail. Using light microscopy and time-lapse imaging of laboratory-reared embryos, we describe the development of Crepidula navicella, a direct developer with nutritive embryos that cleave and gastrulate. Early stages of nutritive and viable embryos do not show any obvious morphological differences, but do show asynchrony in early cleavage among embryos from the same capsule. We discovered that two classes of nutritive embryos are produced; gastrula-like nutritive embryos, which arrest after gastrulation, and post-gastrula-like nutritive embryos that are more variable in morphology, and show evidence of minor differentiation. This study provides a framework for future research on the developmental and molecular mechanisms of nutritive embryo development of C. navicella, which will allow us to address the role of nutritive embryos in the origins of developmental polyphenisms. Careful description of the developmental sequence is necessary before adaptive hypotheses can be addressed, and comparisons with other taxa can be made. Understanding the different ways that embryos and their development are disrupted to produce nutritive embryos will provide important insights into the normal process of development.
当被包裹的胚胎通过取食其正在发育的同胞（即营养胚胎）来完成发育时，就会发生同胞相食现象。营养胚胎存在于多种动物群体中，在一些海洋无脊椎动物群体中尤为常见。尽管同胞相食现象在帽贝科腹足类动物中已经独立进化了很多次，但具有营养胚胎的同胞相食发育尚未得到详细描述。我们利用光学显微镜和对实验室饲养胚胎的延时成像技术，描述了舟形帽贝的发育过程，舟形帽贝是一种具有营养胚胎的直接发育者，其胚胎会进行卵裂和原肠胚形成。营养胚胎和可存活胚胎的早期阶段没有显示出任何明显的形态差异，但同一卵囊中胚胎的早期卵裂显示出不同步性。我们发现产生了两类营养胚胎；类似原肠胚的营养胚胎，在原肠胚形成后停止发育，以及类似原肠胚后期的营养胚胎，其形态变化更大，并显示出轻微分化的迹象。这项研究为未来研究舟形帽贝营养胚胎发育的发育和分子机制提供了一个框架，这将使我们能够探讨营养胚胎在发育多型性起源中的作用。在探讨适应性假说并与其他分类群进行比较之前，仔细描述发育序列是必要的。了解胚胎及其发育被破坏以产生营养胚胎的不同方式，将为正常发育过程提供重要的见解。
