Ecology, evolution and development of a symbiosis between a green alga and some amphibians

共生是一种引人入胜的生物互动，当两个或更多物种以持续的方式互动时，通常是为了互利。这种现象在自然界中很常见，通常涉及生活在光学透明或半透明宿主结构上或内部的较小的自养(自养)共生体。两个著名的例子包括造礁珊瑚和深海喷口生物，前者居住着被称为甲藻的单细胞光合作用有机体，后者居住着吃硫细菌。共生组合在生态上可能极其重要：整个生态系统(例如，大堡礁和深海喷口群落)都是这些共生的结果。尽管有许多光合真核生物与动物共生的例子，但没有观察到地球上最复杂的动物脊椎动物之间的这种相互作用。我们发现，单细胞绿藻(Oophila Amblystomatis)，长期以来一直被认为与黄斑蜥蜴胚胎形成外生共生关系，实际上入侵了它们的胚胎宿主的组织和细胞。现在提出了许多后续问题，本提案旨在回答其中一些问题。 许多北美两栖动物通过将卵块存放在池塘中进行繁殖，另外三种两栖动物与卵黄形成外共生。我们的研究提供了初步证据，表明不同的卵黄血统优先与不同的寄主卵块形成联系。因此，我们的第一个任务是进一步研究宿主-共生体的特异性，因为这可能是确定内共生关联如何进化的第一步。我们工作的第二个方面是找出栖息在卵团中的藻类来自哪里。最明显的地方是寻找池塘水中的藻类，但我们最初的研究表明，母亲正在将藻类传播到它们的卵中，这一过程被称为垂直传播。我们打算测试藻类是从周围的池塘水中获得的，还是从胚胎的父母那里获得的，从而解开这种联系的关键谜团之一。我们的第三个目标是验证一个假设，即藻类通过提供氧气(光合作用的副产品)，增强了胚胎对热应激的耐受性。在气候变暖的情况下，能够预测生物对热应激的反应是很重要的。通过控制卵囊中藻类的数量，我们将能够测试藻类在保护胚胎免受因变暖而造成的压力方面所起的作用。综上所述，我们建议研究这种引人入胜的、新发现的生物相互作用的生态学、进化和发展进程的几个方面。

Symbioses are fascinating biological interactions that occur when two or more species interact in a sustained manner, usually for mutual benefit. This phenomenon is common in nature and often involves smaller autotrophic (self-feeding) symbionts that live on or inside optically transparent or translucent host structures. Two celebrated examples include reef-building corals, which house single celled photosynthetic organisms called dinoflagellates and deep sea vent organisms such as mussels or tube worms, which house sulfur-eating bacteria. Symbiotic associations can be extremely ecologically important: entire ecosystems (e.g., The Great Barrier Reef and Deep Sea Vent Communities) are generated as a result of these symbioses. Despite numerous examples of symbioses between photosynthetic eukaryotes and animals, no such interaction had been observed among vertebrates, the most complex animals on the planet. We discovered that unicellular green algae (Oophila amblystomatis), long known to form an ectosymbiotic association with embryos of the yellow-spotted salamander Ambystoma maculatum actually invade tissues and cells of their embryonic hosts. Many subsequent questions have now been raised and this proposal aims to answer some of them. Many North American amphibians reproduce by depositing egg masses in ponds and three other amphibians form ectosymbioses with Oophila. Our studies provided preliminary evidence that different lineages of Oophila preferentially form associations with each of the different host egg masses. Therefore our first task is to further investigate host-symbiont specificity because it could be the first step to determining how the endosymbiotic association evolved. The second aspect of our work is to find out where the algae that inhabit egg masses are coming from. The most obvious place is to look for the algae in the pond water, but our original work suggested that mothers are transmitting algae to their eggs, a process called vertical transmission. We intend to test whether algae are acquired from surrounding pond water or from the parents of the embryos and therefore solve one of the key mysteries of this association. Our third aim is to test a hypothesis that the algae, through the provision of oxygen (a byproduct of photosynthesis), are conferring upon the embryos increased tolerance to thermal stress. In a warming climate, it is important to be able to predict organismal responses to thermal stress. By manipulating the amount of algae in the egg capsules, we shall be able to test the role that algae play in protecting embryos from stress due to warming. In summary, we propose to examine several aspects of the ecology, evolution and developmental progression of this fascinating, newly discovered, biological interaction.