New research suggests predatory lifestyle shaped early animal evolution

The initial animals that marked the dawn of life on Earth likely followed a predatory lifestyle rather than being filter feeders like modern-day sponges. Recent research led by Prof. Dr. Thomas W. Holstein from Heidelberg University sheds light on the evolution of sea anemones and its connection to predation’s influence on nervous system development.

In a groundbreaking article published in the Proceedings of the National Academy of Sciences, Prof. Holstein’s team revealed that the larvae of the small sea anemone Aiptasia actively hunt and feed on live prey during their early stages, not relying on symbiotic algae. These larvae employ specialized stinging cells and a rudimentary neural network to capture and consume their prey.

Gastrulation, a crucial stage in the embryonic development of multicellular organisms, played a pivotal role. During gastrulation, a hollow sphere of cells, the blastula, transforms into a larval stage with a gut and mouth. This process is universal among animals and could have existed at the inception of animal evolution.

Ira M├Ągele, a member of Prof. Holstein’s research group, demonstrated that Aiptasia sea anemone larvae start capturing appropriately sized prey using their stinging cells even in the late gastrula stage. They ingest and digest this prey in their basic gut.

Aiptasia sea anemones serve as a model system for studying endosymbiosis in corals and other cnidarians. While corals rely on symbiotic algae for nutrition as adults, Aiptasia emphasizes the importance of active predation during the larval stage, which is essential for completing their life cycle.

Laboratory experiments revealed that Aiptasia larvae require small, live food. Nauplius larvae of Tisbe copepods, measuring 50 to 80 micrometers, prove to be ideal nourishment for their growth.

As the larvae grow, they eventually settle on substrates and undergo metamorphosis into primary polyps. This innovative approach allowed researchers to cultivate mature polyps and their offspring successfully.

Dr. Elizabeth Hambleton from the University of Vienna and Prof. Dr. Annika Guse from Ludwig Maximilian University of Munich, both co-authors of the study, emphasize the significance of closing the life cycle of Aiptasia for molecular genetic experiments on this endosymbiotic model organism.

Prof. Holstein’s findings challenge the traditional view of the hypothetical gastrula proposed by evolutionary theorist Ernst Haeckel. While Haeckel’s concept envisioned a particle-filtering life form akin to sponges, the predatory gastrula observed in Aiptasia and other cnidarians possesses specialized stinging cells for hunting prey.

This predatory lifestyle, characterized by extrusive organelles that release toxins (similar to single-celled organisms and simple worms), could have played a pivotal role in driving early multicellular organism evolution and the development of complex, organized nervous systems.

Source: Heidelberg University

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