Elysia Chlorotica

The Eastern Emerald Elysia

Kingdom: Animalia

Phylum: Mollusca

Class: Gastropoda

Order: Sacoglossa

Family: Elysiidae

Genus: Elysia

Species: E. chlorotica

Figure 1. An E. chlorotica specimen

General Characteristics:

The Eastern Emerald Elysia is a species of sea slug with unique photosynthetic abilities. Their bodies are fairly flat and tend to ripple, with a "snail-like" head shape. It can be seen in figure 1 that the Eastern Emerald Elysia are usually a dark green color due to the chlorophyll produced by the chloroplasts residing within some of their cells, although their coloration changes throughout their life cycle and in relation to the health of their chloroplasts. Emerald Elysia often live between nine and ten months, and usually only reach one to six centimeters long.

Habitat:

The Eastern Emerald Elysia reside in salt marshes and inlets along the Atlantic coast of North America. As shown in figure 1 this distribution includes the eastern coast of North America from Nova Scotia to Florida.

Figure 2. Distribution of E. chlorotica

Photosynthesis in Eastern Emerald Elysia:

These Sea Slugs are one of the only animals capable of extracting energy via photosynthesis. This is achieved with kleptoplasty, which is the maintenance of plastids taken from another organism, in this case the Elysia extract chloroplasts from the algae Vaucheria litorea which they feed upon. They ingest them and transport those chloroplasts into their own digestive epithelial cells. These chloroplasts photosynthesize from within the digestive epithelial cells and remain for months at a time, while the sea slug absorbs the carbohydrates resulting from the chloroplasts' photosynthesis.

A study done with wild Eastern Emerald Elysia showed that they can survive for up to ten months while starved of all food but light and carbon dioxide, which indicates that these sea slugs obtain permanent kleptoplasty by the time they fully mature into adults.

Horizontal Gene Transfer:

An especially interesting aspect of this ability is that the chloroplasts themselves do not contain all of the DNA needed to produce the proteins which are required for their normal metabolism (maintenance of the chloroplasts). Elysia is able to produce the required proteins due to horizontal gene transfer, where some of the DNA of the algae V. litorea has been integrated into the genome of E. chlorotica allowing them to produce the necessary proteins to allow plastid metabolism and photosynthesis in the ingested chloroplasts.

Synchronized Death:

Annually adult Emerald Elysia die off within weeks of eachother in the spring of every year after laying eggs. The cells of these sea slugs were found to show signs of apoptosis, programmed cell death, along with degradation of their chloroplasts.

Citations:

Mondy, W. L., & Pierce, S. K. (2005). Apoptotic-like morphology is associated with annual synchronized death in kleptoplastic sea slugs (Elysia chlorotica). Invertebrate Biology, 122(2), 126-137. doi:10.1111/j.1744-7410.2003.tb00078.x

Pelletreau, K. N., Weber, A. P., Weber, K. L., & Rumpho, M. E. (2014). Lipid Accumulation during the Establishment of Kleptoplasty in Elysia chlorotica. PLoS ONE, 9(5). doi:10.1371/journal.pone.0097477

Rafferty, J. P. (2016, November 21). Elysia chlorotica. Retrieved November 30, 2018, from https://www.britannica.com/animal/Elysia-chlorotica

Rumpho, M. E., Worful, J. M., Lee, J., Kannan, K., Tyler, M. S., Bhattacharya, D., . . . Manhart, J. R. (2008). Horizontal gene transfer of the algal nuclear gene psbO to the photosynthetic sea slug Elysia chlorotica. Proceedings of the National Academy of Sciences, 105(46), 17867-17871. doi:10.1073/pnas.0804968105