Unanticipated Research Results: Did Early Animal Life Originate as Predators?
An initial planula larval phase of the sea anemone Aiptasia—indicated by its cyan nuclei and green stinging cells—is shown capturing a crustacean nauplius (in green) belonging to the copepod species Tisbe sp. The image credits go to researchers Ira Mägele and Ulrike Engel.
Newly revealed studies on Aiptasia sea anemones indicate groundbreaking evolutionary phenomena in multicellular life forms.
A pressing question in evolutionary biology is whether the inaugural animal species were predators or rather filter feeders akin to contemporary oceanic sponges. Another aspect to consider is the influence of algae symbiosis, as seen in coral formations that build reefs.
A team of researchers led by Professor Thomas W. Holstein from Heidelberg University has made intriguing discoveries about the evolutionary development of sea anemones. Their studies propose that predatory behavior significantly shaped the evolution of sea anemones, particularly influencing the genesis of their nervous system.
Independent Dietary Behavior in Sea Anemone Larvae
The scientists demonstrated that the young developmental stages, or larvae, of the diminutive sea anemone Aiptasia actively hunt live prey. Contrary to some assumptions, these larvae are not reliant on algae. They employ specialized stinging cells and rudimentary neural circuits to capture their prey.
Significance of Gastrulation in Developmental Biology
Gastrulation is an essential phase in the embryonic development of multicellular beings.
Professor Holstein, a developmental and evolutionary biologist at the Centre for Organismal Studies (COS) at Ruperto Carola, elucidates: “A gastrula evolves from a hollow cellular sphere called a blastula, morphing into a larval stage that possesses a gut and mouth. This phase, known as the gastrula stage, is common to all animals and might also have existed at the onset of animal evolutionary history.”
Research group member Ira Mägele successfully proved that, even at the late gastrula stage, Aiptasia larvae capture appropriately-sized prey using their stinging cells, consume it through their mouth, and digest it within their rudimentary gastrointestinal tract.
Algal Symbiosis and Nutritional Importance
The Aiptasia sea anemone serves as an exemplary system for investigating endosymbiosis in corals and other cnidarians.
Professor Holstein elaborates: “In nutrient-deprived aquatic environments, coral larvae or young polyps incorporate symbiotic algal cells. However, in Aiptasia, this process is crucial for mature individuals but not for the larvae, indicating that nutrition plays a vital role in completing their life cycle.”
Laboratory Observations and Optimal Nutritional Conditions for Larvae
Lab experiments showed that the Aiptasia larvae required prey to be both small and alive. Tisbe copepod nauplius larvae, measuring between 50 and 80 micrometers, met these criteria, providing optimal nourishment.
Continuous and rapid growth of the larvae was observed, ultimately leading to their settling on a substrate and metamorphosing into primary polyps.
Ira Mägele adds: “For the first time, we successfully cultivated mature polyps along with their offspring.”
Dr. Elizabeth Hambleton from the University of Vienna (Austria) emphasized that closing the life cycle of Aiptasia will enable molecular genetic experiments vital for functional studies on this key endosymbiotic model organism.
Professor Dr. Annika Guse from Ludwig Maximilian University of Munich, also a co-author of the study, considers this experimental methodology a landmark achievement for research on this model system.
A Revised View on the Gastrula Hypothesis
The gathered data suggests a revised understanding of predatory behavior as a fundamental attribute of cnidarian gastrulae. The concept of the “gastrula hypothesis” was initially introduced by evolutionary theorist Ernst Haeckel (1834 to 1919).
Professor Holstein notes: “Haeckel’s theoretical gastrula was a filter-feeding entity similar to sponges. However, Aiptasia and other cnidarians possess specialized stinging cells for capturing prey.”
The predatory characteristics of gastrula-like organisms, equipped with toxin-releasing organelles, could have been instrumental in early multicellular evolution and the formation of intricate, organized neural systems, adds the biologist from Heidelberg University.
The study titled “A predatory gastrula leads to symbiosis-independent settlement in Aiptasia” was authored by Ira Mägele, Sebastian Rupp, Suat Özbek, Annika Guse, Elizabeth A. Hambleton, and Thomas W. Holstein, and was published on September 25, 2023, in the Proceedings of the National Academy of Sciences.
Funding for this research was furnished by the German Research Foundation as part of Heidelberg University’s “Mechanisms and Functions of Wnt Signaling” Collaborative Research Centre, along with the ERC Consolidator Grant “SYMCELLS – Resolving the molecular mechanisms of intracellular coral-algal symbiosis” led by Professor Guse.
Frequently Asked Questions (FAQs) about evolutionary development of sea anemones
What is the main focus of the research conducted by Heidelberg University?
The primary focus of the research is to understand the evolutionary development of sea anemones, particularly the Aiptasia species. The study aims to answer whether predatory behavior played a significant role in the early evolutionary stages of multicellular organisms and the formation of their nervous systems.
Who led the research study?
The research study was led by Professor Thomas W. Holstein of Heidelberg University.
What are the key findings of the research?
The key findings suggest that predatory behavior has been instrumental in shaping the evolutionary development of sea anemones. This, in turn, had a significant impact on the early evolution of multicellular organisms, including the development of their nervous systems.
What methods did the researchers use to study Aiptasia sea anemones?
The researchers employed laboratory studies and observations, focusing on the larvae of the Aiptasia sea anemone. They examined their feeding habits, usage of specialized stinging cells, and rudimentary neural circuits.
What is the significance of gastrulation in this study?
Gastrulation is highlighted as a crucial phase in the early embryonic development of multicellular beings. The study proposes that all animals pass through this stage, which might have also existed at the onset of animal evolutionary history.
What role does symbiotic algae play in the life cycle of Aiptasia sea anemones?
While symbiotic algae are crucial for the nutrition of mature Aiptasia sea anemones, the larvae are not dependent on algae. They are primarily predatory and can capture and digest prey independently.
Who funded the research?
The research was funded by the German Research Foundation as part of Heidelberg University’s “Mechanisms and Functions of Wnt Signaling” Collaborative Research Centre and the ERC Consolidator Grant led by Professor Guse.
What implications does this research have for evolutionary biology?
The research provides new insights into the early evolutionary events of multicellular organisms. It particularly revises our understanding of the role predatory behavior may have played in the development of complex, organized nervous systems.
Where was the research published?
The research was published in the Proceedings of the National Academy of Sciences on September 25, 2023. The DOI for the article is 10.1073/pnas.2311872120.
Who are the other participating researchers and institutions?
Dr. Elizabeth Hambleton from the University of Vienna (Austria) and Professor Dr. Annika Guse from Ludwig Maximilian University of Munich were among the other participating researchers.
More about evolutionary development of sea anemones
- Heidelberg University Centre for Organismal Studies
- Proceedings of the National Academy of Sciences
- German Research Foundation
- ERC Consolidator Grant
- Ludwig Maximilian University of Munich Research
- University of Vienna Research Department
- Mechanisms and Functions of Wnt Signaling Collaborative Research Centre