Pictured is an early planula larval stage of the sea anemone Aiptasia (cyan nuclei and green stinging cells) preying on a crustacean nauplius (green) of the copepod Tisbe sp. Credit: Ira Mägele and Ulrike Engel
Key points:
- The larvae of the Aiptasia sea anemone capture small living prey with specialized stinging cells and digest them in their primitive gut.
- For the first time, researchers traced the Aiptasia lifecycle from their predatory larvae stage to their adult form.
- Closing the lifecycle and highlighting the functional nature of larvae improves the understanding of early animal evolution.
New findings, reported in PNAS, reveal that an early predatory lifestyle in sea anemones molded their evolution and the origin of their nervous system.
The Aiptasia sea anemone serves as a model system for endosymbiosis in corals and other cnidarians. While symbiotic processes are critical for survival of adult Aiptasia, they do not contribute to growth and settlement of the larvae and there is no evidence of Aiptasia larvae completing their life cycle by undergoing metamorphosis into adult forms.
Multicellular organisms begin development as a hollow sphere of cells called a blastula. The gastrula develops from those cells to form a larval stage with a gut and a mouth. In this study, researchers demonstrated that during the late gastrula stage, Aiptasia sea anemone larvae capture prey with their specialized stinging cells, ingest them with their mouth, and digest them in their gut.
The new data suggest that this predatory lifestyle of feeding on small live food sources, including the Nauplius larvae of Tisbe copepods, supports Aiptasia development and maturation. As larvae increase rapidly in size, they settle on substrate and undergo metamorphosis into primary polyps. Now, with this knowledge, researchers successfully grew mature polyps and their descendants for the first time.
“By closing the lifecycle of Aiptasia, it will finally be possible to carry out necessary molecular genetic experiments required for functional studies on this key endosymbiotic model organism,” said Annika Guse, professor at Ludwig Maximilian University of Munich.
Aiptasia gastrula excrete toxins that are similar to those found in single-celled organisms and simple worms, suggesting that their predatory behavior likely drove the early evolution of multicellular organisms. Additionally, Aiptasia larvae’s feeding behavior relies on functional stinging cells, which hints at the evolution of complex neuronal control and an organized nervous system. Together, these breakthrough findings offer new perspective on early animal evolution.