Kleptoplasty

Kleptoplasty is a form of cellular sequestration in which a heterotrophic animal intentionally takes up and retains functional plastids, most commonly chloroplasts, from photosynthetic prey. The retained plastids, or kleptoplasts, can remain metabolically active for varying periods, enabling the animal to perform photosynthesis and supplement its energy budget.

The phenomenon is best documented in sacoglossan sea slugs, a group of herbivorous slugs. Species such as Elysia chlorotica, E. timida, and E. viridis have been studied for their ability to sequester chloroplasts from certain algal prey (notably Vaucheria litorea in several studies). After feeding, the slug digestive cells can house intact chloroplasts within specialized cytoplasmic domains, where they continue to function for days to months, depending on species and environmental conditions.

Maintenance of kleptoplasts involves cellular adaptations in the slug that support chloroplast stability, light exposure, and access to inorganic carbon and other substrates. Since most algal nuclei are degraded during prey digestion, the longevity of kleptoplasts generally depends on the chloroplasts’ intrinsic machinery and some residual host factors. The extent to which algal genes or gene products become integrated into the slug’s genome remains debated; current evidence does not indicate widespread horizontal gene transfer to enable long-term plastid autonomy in most cases.

Kleptoplasty raises questions about endosymbiosis, organelle integration, and the evolution of host–symbiont interactions. It provides a unique example of temporary, functional plastid retention outside the plant cell and continues to be an active area of comparative genomics and physiology.