Godhe Anna, Kremp Anke, Montresor Marina
Department of Biological and Environmental Sciences, University of Gothenburg, Box 461, SE 405 30 Göteborg, Sweden.
Marine Research Centre, Finnish Environment Institute (SYKE), Erik Palménin aukio 1, FI-00560 Helsinki, P.O. Box 140 Helsinki, Finland.
Protist. 2014 Aug;165(4):401-16. doi: 10.1016/j.protis.2014.04.006. Epub 2014 May 9.
This study provides microscopic and molecular evidence for sexual reproduction in the homothallic centric diatom Skeletonema marinoi isolated from the Baltic Sea. The species is capable of restoring cell size asexually through an auxospore-like stage. However, cells were sexualized after shifting strains from low (6 PSU) to high (16 PSU) salinity. We observed flagellate male gametes and oogonia, with diameters of 3-4 and 3.2-6.3μm, respectively. Fertilization took place followed by the formation of round auxospores surrounded by thin siliceous incunabular scales. Auxosporulation was synchronized, and a maximum of auxospores was detected on day three following the salinity shift. The proportion of auxospores to vegetative cells ranged from 0.02 to 0.18. There was a significant correlation between auxosporulation success and inoculum cell density. At lower cell concentration (5,000 cells ml(-1)), proportionally fewer auxospores were formed. Auxospores were formed in single strains and in crosses of strains. The proportion of auxospores differed significantly among strains and crosses of strains. Additionally, we isolated single auxospores, obtained F1 strains and performed microsatellite based pedigree analysis of parental generations and their offspring. We proved that the auxospores were formed sexually, either by inter- or by intra-strain fertilization.
本研究为从波罗的海分离出的同宗配合中心硅藻海生骨条藻（Skeletonema marinoi）的有性生殖提供了微观和分子证据。该物种能够通过类似复大孢子的阶段进行无性恢复细胞大小。然而，当菌株从低盐度（6个盐度单位）转移到高盐度（16个盐度单位）时，细胞发生了有性化。我们观察到了鞭毛雄配子和卵囊，其直径分别为3 - 4微米和3.2 - 6.3微米。受精后形成了圆形的复大孢子，周围有薄的硅质初生鳞片。复大孢子形成是同步的，在盐度转移后的第三天检测到最多数量的复大孢子。复大孢子与营养细胞的比例在0.02至0.18之间。复大孢子形成成功率与接种细胞密度之间存在显著相关性。在较低细胞浓度（5000个细胞/毫升）下，形成的复大孢子比例相应较少。复大孢子在单菌株和菌株杂交中形成。不同菌株及其杂交组合中复大孢子的比例差异显著。此外，我们分离了单个复大孢子，获得了F1菌株，并对亲代及其后代进行了基于微卫星的谱系分析。我们证明复大孢子是通过有性方式形成的，要么是菌株间受精，要么是菌株内受精。
