Ocean Sciences Centre, Memorial University, Saint John's, Newfoundland and Labrador A1C 5S7, Canada.
Proc Biol Sci. 2011 Dec 7;278(1724):3517-22. doi: 10.1098/rspb.2011.0605. Epub 2011 Apr 20.
The concept of intraorganismal genetic heterogeneity resulting from allogeneic fusion (i.e. chimerism) has almost exclusively been explored in modular organisms that have the capacity to reproduce asexually, such as colonial ascidians and corals. Apart from medical conditions in mammals, the natural development of chimeras across ontogenetic stages has not been investigated in any unitary organism incapable of asexual propagation. Furthermore, chimerism was mainly studied among gregarious settlers to show that clustering of genetically similar individuals upon settlement promotes the occurrence of multi-chimeras exhibiting greater fitness. The possible occurrence of chimeric embryos and larvae prior to settlement has not received any attention. Here we document for the first time the presence of natural chimeras in brooded embryos and larvae of a unitary cnidarian, the sea anemone Urticina felina. Rates of visible bi- and multi-chimerism of up to 3.13 per cent were measured in the broods of 16 females. Apart from these sectorial chimeras, monitored fusion events also yielded homogeneous chimeric entities (mega-larvae) suggesting that the actual rates of natural chimerism in U. felina are greater than predicted by visual assessment. In support of this assumption, the broods of certain individuals comprised a dominant proportion (to 90%) of inexplicably large embryos and larvae (relative to oocyte size). Findings of fusion and chimerism in a unitary organism add a novel dimension to the framework within which the mechanisms and evolutionary significance of genetic heterogeneity in animal taxa can be explored.
由于异体融合（即嵌合体）而导致的体内遗传异质性的概念几乎仅在具有无性繁殖能力的模块化生物中得到了探索，例如群体海鞘和珊瑚。除了哺乳动物的医学条件外，在任何不能进行无性繁殖的单一生物体中，尚未研究过跨个体发育阶段的嵌合体的自然发育。此外，嵌合体主要在群居定居者中进行研究，以表明定居后遗传相似个体的聚类促进了表现出更高适应性的多嵌合体的发生。在定居之前，嵌合胚胎和幼虫的可能发生尚未受到任何关注。在这里，我们首次记录了单元腔肠动物海葵 U. felina 抱卵胚胎和幼虫中天然嵌合体的存在。在 16 只雌性的卵中，可观察到高达 3.13%的可见双和多嵌合体率。除了这些扇形嵌合体之外，监测到的融合事件还产生了同质嵌合体实体（大型幼虫），这表明 U. felina 中天然嵌合体的实际发生率高于视觉评估所预测的。为了支持这一假设，某些个体的卵中包含了不成比例的大胚胎和幼虫（相对于卵大小），比例高达 90%。在单一生物体中发现融合和嵌合体为探索动物分类群中遗传异质性的机制和进化意义的框架增添了新的维度。
