An organism that both consumes others and undergoes photosynthesis
Energy is essential for carrying out all of life’s vital processes: breaking down, synthesizing, and transporting molecules (5). However, energy cannot be recycled; thus, organisms must find a constant source of energy in the form of food (5). The way an organism acquires energy allows scientists to classify organisms as plants or animals (7). Plants are autotrophs––organisms that sustain themselves by producing food. For example, plants undergo photosynthesis to convert sunlight energy into chemical energy stored in glucose, and use that glucose to produce energy to survive (7). Animals, however, are heterotrophs that are unable to make their own food so rely on other organisms to obtain energy (7). Although this classification is easy to comprehend, Marine Biology Professor Øjvind Moestrup of the University of Copenhagen believes, “The old way of classifying living organisms as animals and plants is too simplistic” (1). Moestrup discovered mesodinium chamaeleon, a microscopic, mixotrophic organism that obtains energy like both an animal––consumes other organisms––and a plant––undergoes photosynthesis (2, 4).
Mesodinium chamaeleon was first found in Nivå Bay of the Baltic Sea in Denmark, but sightings of the organism off the coast of Finland, Chile, and Rhode Island have also been documented (4). Mesodinium chamaeleon lives deep at the bottom of the ocean and feeds off of microorganisms such as algae (1, 2, 4). Depending on the color of algae mesodinium chamaeleon consumes, the organism can turn green, red, or both (4).
So, how does mesodinium chamaeleon get its photosynthetic abilities? The creature is a single-celled ciliate––organism characterized by the presence of cilia or microscopic hairlike structures––and can only be visualized under a powerful microscope (1). Using its hundreds of small hair-like appendages, mesodinium chamaeleon rapidly moves through water and captures its prey (1, 6). Once the algae is ingested into a food vacuole, the flagella of the algae are shed and discharged (6). What remains in the stomach of the mesodinium chamaeleon is an undigested vacuole containing a chloroplast, nucleus, and mitochondria, and the organism can use the chloroplast, an essential organelle for photosynthesis (1, 2, 6, 7). Thus, mesodinium chamaeleon forms an endosymbiotic relationship—both organisms benefit—with the algae (4). While mesodinium chamaeleon is protecting and transporting the algae’s organelles, mesodinium chamaeleon is a plant, producing chemical energy through photosynthesis (4). The organelles can remain intact for several weeks until the organism digests the vacuole (4). After the creature digests its plant components, it exhibits animal-like behaviors, and hunts for new plants (1).
Organisms that undergo significant physical changes throughout their lives remain within the same biological group: a caterpillar transforming into a butterfly remains part of the animal family (4). Mesodinium chamaeleon, however, introduces complexity to the classification of organisms. Currently, the unique organism can only be maintained in a laboratory culture for short periods of time; although the creature eats, it dies after only a few months, limiting the ability to conduct scientific studies (1, 6). Moestrup and his team continue to study mesodinium chamaeleon, hoping to learn more about its unique plant and animal characteristics (1). When and why does the organism choose to switch from plant to animal or vice versa? How much energy does the creature get from photosynthesis and from consuming other organisms? Mesodinium chamaeleon provides insight into endosymbiotic relationships, the evolution of different organelles and cell functions, and mixotrophic organisms (3).
- Ebdrup, N. (2012, January 19). Weird ‘plant-animal’ baffles scientists. Science Nordic. Retrieved from https://sciencenordic.com/animals-biology-denmark/weird-plant-animal-baffles-scientists/1438173
- Johnson, M. (2016, December 20). The Genetic Diversity of Mesodinium and Associated Cryptophytes. Frontiers in Microbiology: Aquatic Microbiology. Retrieved from https://www.frontiersin.org/articles/10.3389/fmicb.2016.02017/full.
- Kim, M. (2019, October 1). Unveiling the hidden genetic diversity and chloroplast type of marine benthic ciliate Mesodinium species. Nature Research. Retrieved from https://www.nature.com/articles/s41598-019-50659-2.
- Mesodinium Chamaeleon Is A Unique Life Form That is Half Plant Half Animal. (2012, January 15). SciTechDaily. Retrieved from https://scitechdaily.com/mesodinium-chamaeleon-is-a-unique-life-form-that-is-half-plant-half-animal/
- Miller, C. (n.d). 4.9 Energy Needs of Living Things. Thompson Rivers University. Retrieved from https://humanbiology.pressbooks.tru.ca/chapter/4-9-energy-needs-of-living-things/.
- Moestrup, O. (2012, January 5). Studies on the genus Mesodinium I: ultrastructure and description of Mesodinium chamaeleon n. sp., a benthic marine species with green or red chloroplasts [Abstract]. Journal of Eukaryotic Microbiology. Retrieved from https://pubmed.ncbi.nlm.nih.gov/22221919/
- Urry, L., Cain, M., Minorsky, P., Wasserman, S., Orr, R. (2021). Campbell Biology: Twelfth Edition . Pearson Education. Retrieved from https://plus.pearson.com/courses/cataldo43349/products/4FHGBOUUFNS/pages/a201f473cccfbf01e6afabdabf673c71fc13d140e?locale=&key=4316419120306558262021.