Kleptoplasty: an unique trophic strategy
Kleptoplasty or kleptoplastidy is a symbiotic phenomenon whereby plastids, (notably chloroplasts), from algae are sequestered by host organisms. The alga is eaten normally and partially digested, leaving the plastid intact. The plastids are maintained within the host, temporarily retaining functional photosynthesis for use by the predator .
This phenomenon occurs in some unicellular organisms such as foraminifera, dinoflagellates and ciliates, but also in a few multicellular organisms.
Among metazoans, retention of functional diet-derived chloroplasts (kleptoplasty) is known only from the sea slug taxon Sacoglossa (Gastropoda - Opisthobranchia). Intracellular maintenance of plastids in the slug’s digestive epithelium has long attracted interest given its implications for understanding the evolution of endosymbiosis.
According to a paper published by Händeler et al. (2011), photosynthetic ability varies widely among sacoglossans; there are three levels of photosynthetic activity: (a) no functional retention; (b) short-term retention lasting about one week; and (c) long-term retention for over a month.
Elysia crispata is one of the species that has a long-term chloroplast retention ability, where other species within the same genus tend to have more short-term retention.
This species can be either heterotrophic or autotrophic throughout their lifespan. As juveniles, food is consumed and digested quickly, with little chloroplast retention. Upon reaching maturity, kleptoplasty becomes an important energy source . Chloroplasts within their parapodia (fleshy dorsal protrusions) continue to produce energy products through carbon fixation throughout their life.
Image: Elysia crispata - ©Zsuzsanna Pusztai