Two important competitive traits in protists, particularly in harmful algal bloom forming species, are lytic toxicity and mixotrophy. This study focuses on Alexandrium pseudogonyaulax, a dinoflagellate species that is both toxic and mixotrophic, and in addition uses a mucus trap to immobilize and capture potential prey. A single strain of A. pseudogonyaulax was subcultured and grown under two different conditions; one subculture was grown autotrophically, while the other was periodically offered algal prey. After 3 yr, the substrain that was fed remained an avid mixotroph, while the autotrophically grown substrain almost completely lost its ability to feed. The emergence of these two “substrains,” with different nutritional strategies, allowed us to investigate possible trade‐offs between lytic toxicity, mixotrophy, and mucus trap production. Both substrains were still capable of producing mucus traps, and successfully captured other cells. Although the nonfeeding substrain lost its ability to feed, it was more lytic than the feeding substrain, which may suggest a trade‐off between lytic toxicity and feeding ability. However, this increased toxicity was not enough to outcompete other faster growing competitors such as Teleaulax acuta and Heterocapsa rotundata. In contrast, the feeding substrain was able to inhibit the growth of these same competing species. The results indicate that for A. pseudogonyaulax, the benefits of phagotrophy far outweigh those of lytic toxicity or the mucus trap alone. The nonfeeding strain used here provides evidence of the loss of mixotrophy under culture conditions, highlighting one of the obstacles in the study of mixotrophic protists.

中文翻译：

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亚历山大假单胞菌的混合营养损失：毒性，粘液陷阱生产和吞噬营养之间权衡的含义。

原生生物，特别是有害藻华形成物种中的两个重要竞争特征是溶解毒性和混合营养。这项研究的重点是有毒和混养性的鞭毛藻亚种Alexandrium pseudogonyaulax，此外还使用粘液诱捕器固定并捕获潜在的猎物。单株拟南芥在两种不同条件下传代培养和生长；一种亚培养自养，而另一种则定期提供藻类猎物。3年后，饲喂的亚菌株仍然是狂热的混合营养菌，而自养的亚菌株几乎完全丧失了其饲喂能力。这两种具有不同营养策略的“亚种”的出现使我们能够研究裂解毒性，混合营养和粘液诱集物生产之间可能的取舍。两种亚菌株仍然能够产生粘液陷阱，并成功捕获了其他细胞。尽管非饲喂亚菌株丧失了其饲喂能力，但它比饲喂亚菌株更具溶解性，这可能表明在溶解性毒性和饲喂能力之间需要权衡。然而，Teleaulax acuta和Heterocapsa rotundata。相比之下，喂食亚株是能抑制这些相同的竞争物种的生长。结果表明，对于A. pseudogonyaulax，phagotrophy的好处远远大于那些溶解的毒性或单独粘液陷阱。这里使用的非饲养菌株提供了在培养条件下混合营养丧失的证据，突显了混合营养原生生物研究中的障碍之一。