These animals are also plants … wait, what? - Luka Seamus Wright

Summary

Elysia chlorotica, a bright green sea slug, is an extraordinary mixotroph that can survive up to a year without eating by photosynthesizing like a plant. It acquires this ability by stealing chloroplasts from algae it consumes, incorporating them into its own cells for both camouflage and nutrition. While many slugs can temporarily retain chloroplasts, Elysia and a few related species uniquely sustain them for months. This fascinating adaptation mirrors ancient events that led to plant evolution. Beyond slugs, mixotrophy is seen in corals, clams, sponges, and algae, allowing survival in nutrient-poor or dark environments and driving oceanic productivity.

Takeaways

• 🪱 Elysia chlorotica, a bright green leaf-like slug, can survive up to a year without eating by photosynthesizing like a plant.
• 🌿 Unlike typical animals (heterotrophs), Elysia is a mixotroph that can both consume food and produce its own energy via photosynthesis.
• 🔬 Elysia steals chloroplasts from algae using its specialized teeth, called radula, incorporating them into its digestive cells.
• 🟢 The incorporated chloroplasts allow the slug to appear leaflike, providing both camouflage and a food source.
• ⏳ While over 70 slug species can steal chloroplasts, only a few, like Elysia, can maintain them for extended periods due to special survival mechanisms.
• 🧬 Elysia adjusts its gene expression and removes damaged chloroplasts to maintain long-term photosynthetic efficiency.
• 🐚 Other organisms, such as corals, clams, and sponges, also rely on symbiotic algae to obtain nutrients through photosynthesis.
• 🌊 Some algae, like Tripos furca, are mixotrophic and can consume microscopic animals, allowing survival in darkness and extreme environments.
• ⚡ The processes observed in Elysia and Tripos provide insight into the evolutionary origin of plants, where early eukaryotes acquired chloroplasts by consuming cyanobacteria.
• 🌍 The repeated transfer of chloroplasts among species contributed to the development of complex plastids and the productivity of oceanic ecosystems.

Q & A

What makes Elysia chlorotica appear similar to a green leaf?

Elysia chlorotica incorporates chloroplasts from the algae it eats into its cells, giving it a bright green color and a leaflike appearance for camouflage and photosynthesis.

How long can Elysia chlorotica survive without eating?

Elysia chlorotica can survive for about a year without eating by living like a plant and using the stolen chloroplasts to photosynthesize.

What is the difference between heterotrophs and autotrophs?

Heterotrophs, like most animals, cannot produce their own food and must consume other organisms. Autotrophs, like plants, can synthesize their own food from sunlight, CO2, and inorganic compounds through photosynthesis.

How does Elysia chlorotica obtain chloroplasts from algae?

Elysia pierces algal cells with its radula, a specialized pointy tooth, sucking out the contents while leaving the chloroplasts intact, which are then incorporated into its own cells.

What distinguishes Elysia and a few related species from other chloroplast-stealing slugs?

Elysia and a few related species can retain chloroplasts for months or even up to a year, whereas most other slugs only keep them for a few weeks.

How do the chloroplasts remain functional inside Elysia?

The chloroplasts can repair their own light-harvesting systems, and the slug adjusts its gene expression to support them while removing damaged plastids to prevent harmful chemical buildup.

What are some other organisms that benefit from photosynthetic symbionts?

Corals, giant clams, and sponges host symbiotic algae that provide organic compounds via photosynthesis, while the host supplies shelter and inorganic compounds.

What is mixotrophy and which organisms in the script are mixotrophs?

Mixotrophy is the ability to both consume other organisms and produce food via photosynthesis. Elysia chlorotica and certain algae like Tripos furca are examples of mixotrophs.

How does Tripos furca survive in darkness?

Tripos furca can consume several microscopic animals per day, allowing it to survive in darkness for weeks, and it can also exchange organelles like chloroplasts with other mixotrophic algae.

How does the process seen in Elysia relate to the origin of plants?

The process is similar to how early single-celled animals consumed cyanobacteria that survived inside them, eventually becoming chloroplasts, and some of these chloroplasts were later hijacked by other organisms, similar to Elysia's chloroplast acquisition.

What evolutionary significance does the chloroplast heist have in oceans?

Repeated acquisition of chloroplasts by different organisms has led to the development of plastids with four membranes, supporting highly productive marine plants and forests and enabling life in areas of the ocean that would otherwise be uninhabitable.