Kleptoplasty and Photosymbiosis in Marine Molluscs

Marine molluscs, particularly sacoglossan sea slugs and some nudibranchs, exhibit remarkable associations with photosynthetic algae or their chloroplasts. In kleptoplasty, chloroplasts (kleptoplasts) are sequestered from algal prey and maintained functionally within host digestive cells, enabling sustained photosynthesis. Photosymbiosis more broadly encompasses stable mutualistic partnerships whereby whole algal symbionts reside in host tissues, transferring photosynthates to the animal partner. These strategies confer ecological advantages such as enhanced survival during food scarcity, contributions to host nutrition and potential gains in reproductive fitness. Retained plastids must withstand host digestive processes and photodamage, requiring adaptations for photoprotection, organelle maintenance and metabolic integration. Host genes involved in immunity and proteolysis appear to mediate plastid incorporation and turnover. Beyond sacoglossans, photosymbiosis is widespread among metazoans—from corals to flatworms—underscoring its evolutionary significance. Studies of symbiont recognition, plastid endurance and host–symbiont metabolic cross-talk are illuminating endosymbiotic origins and hinting at biotechnological applications, including novel bioenergy strategies and insights into resilience against environmental change. The global importance of these systems lies in their impact on marine primary productivity, nutrient cycling and the health of coral reef and seagrass ecosystems.

Research from Nature Portfolio

Recent investigations have deepened understanding of kleptoplast contribution to host metabolism. One study demonstrated light-dependent incorporation of carbon and nitrogen derived from functional kleptoplast photosynthesis, tracking labelled metabolites into host tissues and reproductive organs, which suggests a direct role in reproductive fitness. Another experiment on Elysia viridis under variable light and starvation conditions revealed that slugs with active kleptoplasts experienced reduced weight loss when illuminated, underlining the nutritional relevance of stolen chloroplasts during food deprivation. Complementing these findings, a lipidomic analysis comparing macroalgal chloroplast lipids with those in sequestering slugs showed minimal alteration of glycolipid and sulfolipid profiles post-sequestration, indicating preservation of photosynthetic machinery within the animal host.

Kleptoplasty and Photosymbiosis in Marine Molluscs publication trend

The graph below shows the total number of articles in kleptoplasty and photosymbiosis in marine molluscs across all publications each year (not limited to Nature Index journals).

Technical terms

Kleptoplasty: The process by which animal hosts sequester and maintain functional algal chloroplasts within their cells.

Photosymbiosis: A mutualistic association in which photosynthetic organisms live within or on a host, exchanging metabolic products.

Kleptoplast: A chloroplast stolen from algal prey and retained in a non-photosynthetic host cell.

Photosynthate: Organic compounds produced by photosynthesis that are translocated to and utilised by the host organism.

References

1. The highly developed symbiotic system between the solar-powered nudibranch Pteraeolidia semperi and Symbiodiniacean algae. iScience (2023).
2. Polymorphic adaptations in metazoans to establish and maintain photosymbioses. Biological Reviews (2018).
3. Kleptoplast photosynthesis is nutritionally relevant in the sea slug Elysia viridis. Scientific Reports (2017).
4. Chloroplast acquisition without the gene transfer in kleptoplastic sea slugs, Plakobranchus ocellatus. eLife (2021).
5. Kleptoplasty does not promote major shifts in the lipidome of macroalgal chloroplasts sequestered by the sacoglossan sea slug Elysia viridis. Scientific Reports (2017).
6. Functional kleptoplasts intermediate incorporation of carbon and nitrogen in cells of the Sacoglossa sea slug Elysia viridis. Scientific Reports (2020).