We observed four Gomphonema taxa with a high abundance of Janus cells, which are cells that have valves of two different morphologies, also termed heterovalvar cells. The specimens were collected from a habitat with periodic drying, alternating with standing water. A high proportion of Gomphonema Janus cells (up to 20% of the frustules for each taxon) were found. Heterovalvy within a frustule is based on stria count, and two types of heterovalvy were observed. Cells produced either coarsely or finely striated valves with discontinuous phenotypic plasticity or highly variable stria density within a frustule along a continuous phenotypic gradient. In our study, we measured stria density in complete frustules and single valves. Other features of the frustules showed no noticeable variation. Variable stria density was found in frustules and single valves, although it is not possible to determine whether the single valves were part of Janus cells or homomorphic frustules. Therefore, our conclusions are based on the measurements of complete frustules only. We propose that Janus cells result from two ecophenotypic responses (reaction norm and polyphenism) of these taxa to one or more environmental factors. As such, Gomphonema taxa that produce Janus cells may be model organisms for deciphering the genetic basis of developmental plasticity in diatoms.

中文翻译：

---

硅藻的表型可塑性：四种 Gomphonema 分类群中的 Janus 细胞

我们观察到四个具有高丰度 Janus 细胞的 Gomphonema 分类群，这些细胞具有两种不同形态的瓣膜，也称为异瓣细胞。标本是从栖息地收集的，定期干燥，与静水交替。发现了高比例的 Gomphonema Janus 细胞（每个分类群高达 20% 的硅藻壳）。硅藻壳内的异型瓣膜基于纹路计数，并观察到两种类型的异型瓣膜。细胞沿着连续的表型梯度在硅藻壳内产生具有不连续表型可塑性或高度可变的条纹密度的粗或细条纹瓣膜。在我们的研究中，我们测量了完整硅藻壳和单瓣膜的条纹密度。硅藻壳的其他特征没有显示出明显的变化。在硅藻壳和单瓣膜中发现了可变条纹密度，尽管无法确定单瓣膜是 Janus 细胞的一部分还是同形硅藻壳。因此，我们的结论仅基于完全硅藻壳的测量。我们提出 Janus 细胞是由这些分类群对一种或多种环境因素的两种生态表型反应（反应规范和多态性）引起的。因此，产生 Janus 细胞的 Gomphonema 分类群可能是破译硅藻发育可塑性遗传基础的模式生物。我们提出 Janus 细胞是由这些分类群对一种或多种环境因素的两种生态表型反应（反应规范和多态性）引起的。因此，产生 Janus 细胞的 Gomphonema 分类群可能是破译硅藻发育可塑性遗传基础的模式生物。我们提出 Janus 细胞是由这些分类群对一种或多种环境因素的两种生态表型反应（反应规范和多态性）引起的。因此，产生 Janus 细胞的 Gomphonema 分类群可能是破译硅藻发育可塑性遗传基础的模式生物。