Light microscope pictures of euglenoid cysts from the Triassic-Jurassic border (approx. 200 million years old) in the Schandelah-1 core in Germany (left) and from Triassic sediments in Winterswijk, the Netherlands (right). The specimens are in between 20 and 30 micrometers in size. Credit: Bas van de Schootbrugge, Utrecht UniversityA 400-million-year evolutionary history.Euglenoids, a distinct group of single-celled protists, inhabit a mystical specific niche, being neither totally plant nor animal. Unlike plants that entirely count on photosynthesis, or animals that consume, euglenoids welcome both modes. They browse the dim waters of shallow freshwater ponds, moved by their elongated flagella, taking in raw material while concurrently harnessing their chloroplasts to transform CO2, water, and light into sugars.This double nature positions euglenoids near the foundational root of the eukaryotic branch on the life tree, encompassing animals, plants, and fungis. In spite of their ancient origins, believed to date back over 1 billion years, euglenoids have actually left behind an extremely sparse fossil record.In a brand-new research study published in the journal Review of Palaeobotany and Palynology, a team of Dutch, American, British, German, and Australian researchers shed brand-new light on a group of “bothersome” microfossils that have remained a secret for almost a century. By comparing microscopic fossil cysts in 200-million-year-old pond sediments from cores drilled in Germany and the Netherlands to much older Paleozoic, and much more youthful remains in Holocene lakes in Greece, and finally to living protists in a pond in Australia, the researchers develop a 400-million-year evolutionary history of the euglenoids.Transmission Electron Microscope (TEM) picture of the wall structure of a Holocene euglenoid cyst from Lake Vouliagmeni, Greece. Credit: Wilson Taylor, University of Wisconsin– Eau ClaireWhats in a name?In 2012, Bas van de Schootbrugge, then at the Goethe University in Frankfurt am Main, and Paul Strother from Boston College, while dealing with a range of troublesome microfossils in sediments from around the Triassic-Jurassic border, understood that the circular striated cysts they were seeing, could be in truth euglenoid cysts.” We had this incredible drill core material at our disposal which contained numerous unknown microfossils, consisting of a few of the earliest butterfly remains that we released on in 2018,” stated Bas van de Schootbrugge, now at Utrecht University. Paul Strother continued: “Some of the microfossils we came across revealed a canny similarity to cysts of Euglena, a modern agent that had been explained by Slovakian coworkers. The problem was, there was only one publication in the world making this claim.” Video stills from encysting Euglena from New South Wales, Australia. Credit: Fabian Weston, Protist Lab Films, GalstonEven more disturbing: after a substantial literature evaluation, van de Schootbrugge and Strother realized that the very same kind of microfossil had been given various names. Researchers working on Quaternary and Holocene time slices utilized Concentricystes, referring to a possible algal cyst with concentric ribs. Mesozoic employees used Pseudoschizaea, initially believing it might have been a fern spore. Even older fossils from the Permian, Devonian, Silurian, and Ordovician were referred to as Circulisporites and Chomotriletes.Transmission electron microscopyAfter the authors had disentangled the taxonomic confusion, compiling while doing so almost 500 literature sources related to any of the four taxa, advanced microscope strategies were required to develop the ultrastructure of the cysts with the assistance of transmission electron microscopy (TEM). This needed picking of single specimens, embedding, and micro-tome slicing by University of Wisconsin-Eau-Claire co-author Wilson Taylor. Since the specimens in the Triassic-Jurassic cores were primarily harmed, the group turned to palynologist Andreas Koutsodendris at Heidelberg University (Germany), who had access to Holocene and Pliocene core samples including abundant well-preserved specimens.Light microscopic lense images of euglenoid cysts from Holocene to current Lake Vouliagmeni in Greece. Specimens are between 20 and 30 micrometers in diameter. Keep in mind the fingerprint-like patterning that is a shared quality of all fossil types. Credit: Andreas Koutsodendris, Heidelberg UniversityAndreas Koutsodendris said: “I am experiencing these cysts regularly in cores drilled in lakes, for example in Lake Vouliagmeni in Greece that we studied here, however their biological affinity has actually never ever been cleared. In reality, the cysts are typically figured in publications by colleagues, but nobody had the ability to really put a finger on it.” Wilson Taylor continued: “We were much surprised by the ultrastructure of the cysts. The structure of the wall does not resemble anything that is known. The ribs are not accessories, like in pollen and spores, however part of the wall structure,” said Wilson Taylor. “The layered structure of the walls is also clearly different from lots of other fresh-water green algae,” Taylor continued.Nagging uncertaintyWhile the TEM analysis initially included more secret, the outcomes did line up with a research study published in 2021 by another group of colleagues that looked at the ultrastructure of Pseudoschizaea. A minimum of it was possible to reveal that Holocene and Pliocene Concentricystes and Jurassic Pseudoschizaea are in reality the same. However there remained one nagging unpredictability which was the lack of any cysts produced by living euglenoids. Wilson Taylor: “We did get in touch with numerous biologists working on living euglenoids, but no one had actually had the ability to make euglenoids encyst in a lab setting, enabling for extraction and TEM analyses of the cysts”. Tiny life down underEnter Fabian Weston. By possibility, Strother and van de Schootbrugge came across superb video product published on YouTube by microscopy lover Fabian Weston from Sydney, Australia. In 2020 Fabian Weston had put a drop of water sampled from a nearby pond in New South Wales on a microscope slide, and using his advanced set-up at The Protist Lab filmed Euglena as it gracefully moved in and out of focus.For reasons that stay improperly comprehended but might be associated with the drying out of the water under the coverslip, Euglena is then seen to ball up and form a thick wall with ribs that belongs to the cysts found throughout the fossil record. “Unwittingly, Fabian supplied a crucial piece of proof. He is most likely the only individual in the world to have actually experienced Euglena encyst under a microscopic lense,” Strother said.Significance and next stepsBased on all the offered pieces of the puzzle, the authors hence connect euglenoids from a pond in Australia to fossil cysts that are more than 400 million years old, establishing a deep time record of the euglenoids.” This unlocks for recognizing even older examples, for instance from Precambrian records that go back to the extremely root of the eukaryotic tree of life,” Strother said. “Now that we understand which organisms produced those cysts, we can also utilize them for paleo-environmental interpretations. Their abundance around 2 of the biggest mass-extinction events of the past 600 million years is a telltale indication of some significant turmoils on the continents connected to increased precipitation under extreme greenhouse climate conditions.” Van de Schootbrugge concluded: “Perhaps associated to their abilities to encyst, these organisms have actually endured and made it through every significant termination in the world. Unlike the behemoths that were carried out in by volcanoes and asteroids, these small creatures have actually weathered everything.” Extending their research, the group intends to take a trip to Australia in the near future to scour for preserved Euglena cysts in pond and lake sediments in New South Wales.Reference: “Recognition of an extended record of euglenoid cysts: Implications for the end-Triassic mass extinction” by Bas van de Schootbrugge, Andreas Koutsodendris, Wilson Taylor, Fabian Weston, Charles Wellman and Paul K. Strother, 21 December 2023, Review of Palaeobotany and Palynology.DOI: 10.1016/ j.revpalbo.2023.105043.
By comparing tiny fossil cysts in 200-million-year-old pond sediments from cores drilled in Germany and the Netherlands to much older Paleozoic, and much younger remains in Holocene lakes in Greece, and lastly to living protists in a pond in Australia, the scientists establish a 400-million-year evolutionary history of the euglenoids.Transmission Electron Microscope (TEM) image of the wall structure of a Holocene euglenoid cyst from Lake Vouliagmeni, Greece. Credit: Wilson Taylor, University of Wisconsin– Eau ClaireWhats in a name?In 2012, Bas van de Schootbrugge, then at the Goethe University in Frankfurt am Main, and Paul Strother from Boston College, while working on a variety of troublesome microfossils in sediments from around the Triassic-Jurassic boundary, realized that the circular striated cysts they were seeing, could be in truth euglenoid cysts. Wilson Taylor: “We did get in touch with several biologists working on living euglenoids, but no one had been able to make euglenoids encyst in a lab setting, allowing for extraction and TEM analyses of the cysts”. He is most likely the only person on the planet to have witnessed Euglena encyst under a microscope,” Strother said.Significance and next stepsBased on all the offered pieces of the puzzle, the authors therefore connect euglenoids from a pond in Australia to fossil cysts that are more than 400 million years old, establishing a deep time record of the euglenoids. Extending their research, the team means to take a trip to Australia in the near future to scour for preserved Euglena cysts in pond and lake sediments in New South Wales.Reference: “Recognition of a prolonged record of euglenoid cysts: Implications for the end-Triassic mass termination” by Bas van de Schootbrugge, Andreas Koutsodendris, Wilson Taylor, Fabian Weston, Charles Wellman and Paul K. Strother, 21 December 2023, Review of Palaeobotany and Palynology.DOI: 10.1016/ j.revpalbo.2023.105043.
