Zygotic Icthal factors in intraspecific crosses and reproductive isolation of hybrid inviability between mating-groups of Closterium ehrenbergii.

我们从日本、台湾、尼泊尔和澳大利亚的水田、池塘和湖泊中采集了许多不同种群，并对其进行了生物系统的研究，迄今为止，主要基于性隔离识别出了十几个交配群（从a到P）。形态学和细胞学研究，以及对合子前和合子后分离的生殖障碍的研究，清楚地表明这种藻类的每个交配群都是一个生物物种。在本项目中，我们重点研究了两个不同交配群体的艾伦伯氏梭菌。也就是说，一类是A类，其中自然种群受到季节性和/或偶尔发生的干旱和/或极端高温和低温的条件，至少一次选择，以防止影响合子形成和萌发的性过程的任何有缺陷的突变。另一类是P群，其自然种群仅靠营养细胞分裂而不有性生殖而维持多年。(1)虽然正负两种交配类型在欧洲的一个地方同时存在，但我们还没有发现这两种交配类型同时存在的任何地方，到目前为止在日本收集的所有样本只含有一种交配类型的营养细胞。在北海道东北部和中部、秋田、岩手、山形和福岛发现了纯正型自然种群，在北海道西南部、新潟、长野、富山、山梨县和静冈发现了纯负型自然种群。基于同一自然群体中几乎所有可能组合的杂交，我们发现了显性或交配型加特异性的无杂种突变。(2)虽然在A组中没有检测到这些致死性的合子因子，但在同亲本系的自交和回交F_1后代中发现了较强的近交抑制。

We have studied biosystematically many and various populations of Closterium ehrenbergii sampled from paddy fields, ponds and lakes in Japan, Taiwan, Nepal and Australia, and recognized so far more than a dozen mating groups (from A to P) primarily based on sezual isolation. Morphological and cytological studies, as well as those on the reproductive barriers of pre- and post-zygotic isolation, clearly suggest that each mating group of this alga be a biological species. In this project, we focused to study two contrasting mating groups of Closterium ehrenbergii. Namely, one is Group A of which natural populations are subjected to the conditions that seasonal and/or occasional occurrences of drought and/or extremely high and low temperatures would select, at least once a hear, against any defective mutation that affects the sezual process of zygote formation and germination. The other is Group P of which natural populations are maintained for many years only by means of vegetative cell divisions without sexual reproduction.(1) Although both mating types, plus and minus, coexist in single localities in Europe, we have not yet found any place where both the two coexist and all the samples collected so far in Japan contained vegetative cells of only one mating type. Natural populations of only plus were found in north-eastern and central Hokkaido, Akita, Iwate, Yamagata and Fukushima, and those of only minus were found in south-western Hokkaido, Niigata, Nagano, Toyama, Yamanashi and Shizuoka. Based on crossings in almost all possible combinations among isolates from one natural population, we found a dominant or mating-type plus specific, asynaptic mutation.(2) Although we could not detect such lethal zygotic factors in Group A, we found strong inbreeding depression in selfing and backcrossing F_1 progeny to the same parental strains.