Switching from asexual to sexual reproduction in the planarian Dugesia ryukyuensis:: Bioassay system and basic description of sexualizing process
Switching from asexual to sexual reproduction in the planarian Dugesia ryukyuensis:: Bioassay system and basic description of sexualizing process
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DOI：
10.2108/zsj.16.291
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发表时间：
1999-04-01
影响因子：
0.9
通讯作者：
Hoshi, M
中科院分区：
文献类型：
--
作者：
Kobayashi, K;Koyanagi, R;Hoshi, M
本文建立了一个用卵生性成熟的褐头蛭（Bdellocephala brunnea）虫体诱导琉球三角洲（Dugesia ryukyuensis）OH株有性生殖的试验系统。在该试验系统中，无性生殖的蠕虫逐渐分化出性器官，即卵巢、精巢、生殖孔和卵黄腺，并最终交配和产下充满受精卵的茧。虽然OH株蠕虫被认为没有任何性器官，但通过深入的组织学研究发现了一对未发育的卵巢和少量的卵原细胞。沿着性化的进程，可分为5个阶段：第1阶段，卵巢变大，外观明显;第2阶段，卵母细胞首先出现;第3阶段，原始睾丸出现;第4阶段，生殖孔开放，卵黄腺原基发育，精母细胞出现;第5阶段，成熟精子和卵黄腺形成。如果取食B，则第1、2阶段的蠕虫恢复无性繁殖，但在以后阶段则不恢复。此外，当在第3阶段开始的蠕虫被切断卵巢后部时，所有的尾部再生体最终发育成完全性化的蠕虫。考虑到这些结果，我们得出结论，性化的过程在第二阶段和第三阶段之间有一个不归点。睾丸，甚至是原基，也可能在性的维持和发展中起着重要的作用。
An assay system has been established for the sexual induction in the OH strain, an exclusively fissiparous (asexual) strain, of Dugesia ryukyuensis by feeding them with sexually matured worms of Bdellocephala brunnea, an exclusively oviparous (sexual) species. In this assay system, asexual worms gradually differentiated sexual organs, namely the ovary, testis, genital pore and yolk gland in this order, and eventually mated and laid cocoons filled with fertilized eggs. Although the OH strain worms were believed not to have any sexual organs, a pair of undeveloped ovaries with a few oogonia were detected by an intensive histological search. Along with the progression of sexualization, five distinct stages were histologically recognized: In the first stage, the ovaries became larger enough to be externally apparent; oocytes appeared first at stage 2; the primordial testes emerged at stage 3; a genital pore opened, yolk gland primordia developed and spermatocytes appeared at stage 4; and finally at stage 5 matured spermatozoa and yolk glands were formed. Worms in stages 1 and 2 but not in later stages returned asexual if feeding on B, brunnea was interrupted. Furthermore, when the worms at stage 3 onwards were cut posterior to the ovaries, all the tail regenerants developed eventually into fully sexualized worms. Taking these results in account, we have concluded that the process of sexualization has a point-of-no-return between stages 2 and 3. It is likely also that the testes, even the primordia, play an important role in the maintenance and development of sexuality.