Watson W H, Bourque K M F, Sullivan J R, Miller M, Buell A, Kallins M G, Curtis N E, Pierce S K, Blackman E, Urato S, Newcomb J M
Department of Biological Sciences, University of New Hampshire, Durham, NH 03824, USA.
Department of Pediatrics, Johns Hopkins Hospital, Baltimore, MD 21287, USA.
Integr Org Biol. 2021 May 21;3(1):obab015. doi: 10.1093/iob/obab015. eCollection 2021.
A number of nudibranchs, including and , harbor symbiotic photosynthetic zooxanthellae. spends most of its adult life on seagrass or kelp, capturing planktonic organisms in the water column with a large, tentacle-lined oral hood that brings food to its mouth. also has an extensive network of digestive diverticula, located just beneath its translucent integument, that are typically filled with pigmented material likely derived from ingested food. Therefore, the focus of this project was to test the hypothesis that accumulates symbiotic photosynthetic dinoflagellates in these diverticula. First, we conducted experiments to determine if exhibits a preference for light, which would allow chloroplasts that it might be harboring to carry out photosynthesis. We found that most preferred shaded areas and spent less time in direct sunlight. Second, we examined the small green circular structures in cells lining the digestive diverticula. Like chlorophyll, they exhibited autofluorescence when illuminated at 480 nm, and they were also about the same size as chloroplasts and symbiotic zooxanthellae. However, subsequent electron microscopy found no evidence of chloroplasts in the digestive diverticula of ; the structures exhibiting autofluorescence at 480 nm were most likely heterolysosomes, consistent with normal molluscan digestion. Third, we did not find evidence of altered oxygen consumption or production in housed in different light conditions, suggesting the lack of any significant photosynthetic activity in sunlight. Fourth, we examined the contents of the diverticula, using HPLC, thin layer chromatography, and spectroscopy. The results of these studies indicate that the diverticula did not contain any chlorophyll, but rather harbored other pigments, such as astaxanthin, which likely came from crustaceans in their diet. Together, all of these data suggest that does sequester pigments from its diet, but not for the purpose of symbiosis with photosynthetic zooxanthellae. Considering the translucent skin of , the pigmented diverticula may instead provide camouflage.
许多裸鳃亚目动物，包括[具体物种1]和[具体物种2]，体内共生着光合虫黄藻。[具体物种1]成年后的大部分时间都生活在海草或海带中，它用一个长有触手的大口捕捉水柱中的浮游生物，将食物送入口中。[具体物种1]还有一个广泛的消化盲囊网络，位于其半透明的外皮之下，这些盲囊通常充满了可能来自摄入食物的色素物质。因此，本项目的重点是检验[具体物种1]在这些盲囊中积累共生光合甲藻的假设。首先，我们进行了实验，以确定[具体物种1]是否表现出对光的偏好，这将使它可能含有的叶绿体能够进行光合作用。我们发现，大多数[具体物种1]更喜欢阴暗的区域，在直射阳光下停留的时间较少。其次，我们检查了消化盲囊内衬细胞中的绿色小圆形结构。与叶绿素一样，它们在480纳米的光照下会发出自发荧光，而且它们的大小也与叶绿体和共生虫黄藻大致相同。然而，随后的电子显微镜检查发现，[具体物种1]的消化盲囊中没有叶绿体的迹象；在480纳米处发出自发荧光的结构很可能是异溶酶体，这与正常的软体动物消化过程一致。第三，我们没有发现处于不同光照条件下的[具体物种1]的氧气消耗或产生有变化的证据，这表明在阳光下缺乏任何显著的光合活动。第四，我们使用高效液相色谱法、薄层色谱法和光谱法检查了盲囊的内容物。这些研究结果表明，盲囊中不含任何叶绿素，而是含有其他色素，如虾青素，这些色素可能来自它们饮食中的甲壳类动物。总之，所有这些数据表明，[具体物种1]确实从其饮食中摄取色素，但并非用于与光合虫黄藻共生。考虑到[具体物种1]半透明的皮肤，有色素的盲囊可能反而起到了伪装的作用。
