Growing evidence suggests that sexual reproduction might be common in unicellular organisms, but observations are sparse. Limited knowledge of sexual reproduction constrains understanding of protist ecology. Although Teleaulax amphioxeia and Plagioselmis prolonga are common marine cryptophytes worldwide, and are also important plastid donors for some kleptoplastic ciliates and dinoflagellates, the ecology and development of these protists are poorly known. We demonstrate that P. prolonga is the haploid form of the diploid T. amphioxeia and describe the seasonal dynamics of these two life stages. The diploid T. amphioxeia dominates during periods of high dissolved inorganic nitrogen (DIN) and low irradiance, temperature, and grazing (winter and early spring), whereas the haploid P. prolonga becomes more abundant during the summer, when DIN is low and irradiance, temperature, and grazing are high. Dimorphic sexual life cycles might explain the success of this species by fostering high genetic diversity and enabling endurance in adverse conditions.

越来越多的证据表明，有性生殖在单细胞生物中可能很常见，但观察结果很少。有性生殖的有限知识限制了对原生生态学的理解。虽然Teleaulax amphioxeia和Plagioselmis prolonga是世界范围内常见的海洋隐生植物，并且也是一些 kleptoplastic 纤毛虫和甲藻的重要质体供体，但这些原生生物的生态学和发育情况却鲜为人知。我们证明了P. prolonga是二倍体T. amphioxeia的单倍体形式，并描述了这两个生命阶段的季节性动态。二倍体T. amphioxeia在高溶解无机氮 (DIN) 和低辐照度、温度和放牧期间（冬季和早春）占主导地位，而在夏季，当 DIN 低且辐照度、温度和放牧时，单倍体P. prolonga变得更加丰富很高。二态性生命周期可能通过培养高度的遗传多样性和在不利条件下的耐力来解释该物种的成功。