Jenkins Helen L, Waeschenbach Andrea, Okamura Beth, Hughes Roger N, Bishop John D D
Marine Biological Association of the United Kingdom, Plymouth, Devon, United Kingdom.
Department of Life Sciences, Natural History Museum, London, United Kingdom.
PLoS One. 2017 Jan 17;12(1):e0170010. doi: 10.1371/journal.pone.0170010. eCollection 2017.
Polyembryony-the production of multiple cloned embryos from a single fertilised egg-is a seemingly paradoxical combination of reproductive modes that nevertheless persists in diverse taxa. We document features of polyembryony in the Cyclostomata (Bryozoa)-an ancient order of modular colonial marine invertebrates-that suggest a substantial reduction in the paradoxical nature of this enigmatic reproductive mode. Firstly, we provide molecular evidence for polyembryony in three exemplar species, supporting the widely cited inference that polyembryony characterises the entire order. Secondly, genotyping demonstrates protracted release of cloned offspring from the primary embryo in a given gonozooid (chamber for embryonic incubation), thus exposing the same genotype to changing environmental conditions over time. Finally, we confirm that each gonozooid produces a distinct genotype, with each primary embryo being the result of a separate fertilisation event. We hypothesise that the sustained release of one or a few genotypes against varying environmental conditions achieves levels of risk-spreading similar to those in organisms that release multiple, unique genotypes at a single time. We argue that polyembryony, specifically with the production of a large number of progeny per fertilisation event, has been favoured in the Cyclostomata over long geological periods.
多胚生殖——从单个受精卵产生多个克隆胚胎——是一种看似矛盾的生殖方式组合，但仍存在于多种生物分类群中。我们记录了苔藓虫纲（苔藓虫）中的多胚生殖特征，苔藓虫纲是一种古老的模块化群体海洋无脊椎动物，这表明这种神秘生殖方式的矛盾性大幅降低。首先，我们为三个示例物种的多胚生殖提供了分子证据，支持了被广泛引用的推断，即多胚生殖是整个苔藓虫纲的特征。其次，基因分型表明，在给定的生殖个体（胚胎孵化腔）中，克隆后代从初级胚胎中持续释放，从而使同一基因型随时间暴露于不断变化的环境条件下。最后，我们证实每个生殖个体产生独特的基因型，每个初级胚胎都是单独受精事件的结果。我们推测，在不同环境条件下持续释放一种或几种基因型所实现的风险分散水平，与一次释放多种独特基因型的生物体相似。我们认为，在漫长的地质时期里，苔藓虫纲中多胚生殖，特别是每次受精事件产生大量后代的情况，一直受到青睐。
