Switching of Reproductive Strategy in planarian

各种后生动物可以以多种方式繁殖，并根据环境条件和/或生命周期的不同阶段选择替代的生殖策略，如无性或有性，以及双亲或单亲。然而，生殖模式的选择和切换背后的机制仍有待探索。许多淡水浮游生物通过横向分裂和有性交配进行无性繁殖。无性蠕虫不形成任何性器官，而有性虫有两性的性器官，不会发生分裂。同一物种内的一些种群会季节性地切换这些繁殖模式。我们建立了一个实验系统来分析龙须菜从无性繁殖到有性繁殖的机制。如果该物种的完全无性克隆(OH品系)的蠕虫被喂以完全有性行为的Bdellocephala brunnea的性成熟蠕虫，所有这些蠕虫都会在几周内逐渐发育出卵巢、睾丸和其他性器官，然后交配，最终产下充满受精卵的茧。这表明，性成熟蠕虫含有一种假定的性感化物质(S)，这种物质并不是非常针对特定的属。完全性化的OH蠕虫(获得性)会产生它们自己的性化物质。缺少性欲物质的头部片段再生为无性个体，而含有性欲物质的其他部分再生为有性个体。因此，最有可能的是，它们通过产生足够数量的性刺激物质来保持性欲。我们正在努力鉴定获得性伴侣中的性欲物质，到目前为止，我们已经澄清了它是酸性的，热稳定的，小于0.5 kDa，耐链霉酶。核磁共振分析表明，L色氨酸是性爱物质的候选者之一

Various metazoans can reproduce in multiple ways and select an alternative reproductive strategy such as asexual or sexual, and biparental or uniparental depending upon the environmental conditions and/or the phase of life cycle. However, the mechanism underlying the selection and switch of reproductive modes remains to be explored. Many freshwater planarians reproduce asexually by transverse fission as well as sexually by copulation. Asexual worms do not form any sexual organs, while sexual ones have hermaphroditic sexual organs and do not undergo fission. Some populations within the same species switch these reproductive modes seasonally.We have established an experimental system to analyze the mechanism underlying the switch from asexual to sexual reproduction in the planarian, Dugesia ryukyuensis. If the worms of an exclusively asexual clone (OH strain) of the species are fed with sexually mature worms of Bdellocephala brunnea, an exclusively sexual species, all of them gradually develop ovaries, testes and other sexual organs within a few weeks, and then copulate, and eventually lay cocoons filled with fertilized eggs. This suggests that sexually mature worms contain a putative sexualizing substance(s) that is not very genus-specific. The fully sexualized OH worms (acquired sexuals) produce their own sexualizing substance. The head fragments lacking the sexualizing substance regenerated into asexuals, though the other portions containing the sexualizing substance regenerated into sexuals. Thus, it is most likely that they keep the sexuality by producing enough an amount of the sexualizing substance. We are trying to identify the sexualizing substance in the acquired sexuals, and have so far clarified that it is acidic, heat-stable, smaller than 0.5 kDa and pronase-resistant. NMR analysis showed that L-trp is one of candidate for sexualizing substances