In December 2021, I was awarded the Paul van Oye-prize for my PhD thesis! The Paul van Oye-prize is awarded every two years by the Royal Flemish Academy of Belgium for Science and the Arts (KVAB) to a major work in the field of Biology. Receiving this award represents a strong recognition for my research!
More info here.
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Wil je meer weten over ons meest recente onderzoek over kiezelwieren en klimaatveranderingen in Antarctica? Check de website van de Universiteit Gent!
Our September 15th publication in Science Advances, entitled Extinction of austral diatoms in response to large-scale climate dynamics in Antarctica, reached the Science Advances highlights, and was displayed on the homepage of the Science Advances website! In addition, the paper made it onto the homepage of the Science website: Pinseel E., Van de Vijver B., Wolfe A.P., Harper M., Antoniades D., Ashworth A.C., Ector L., Lewis A.R., Perren B., Hodgson D.A., Sabbe K., Verleyen E., Vyverman W. Extinction of austral diatoms in response to large-scale climate dynamics in Antarctica. Science Advances 7: eabh3233. full text In recent years, microbial biogeography has been extensively studied, revealing that several protists show restricted, rather than cosmopolitan, distributions. However, it remains unclear to what extent microbial communities are impacted by past tectonic and paleoclimate events. This is because no fossil record exists for many micro-organisms, complicating analyses on historical biogeography. When fossil records do exist, such as is the case for diatoms (a group of unicellular algae), they are largely restricted to marine environments which harbor rich fossil records dating back millions of years. Consequently, the link between past climate and diatom evolution has been extensively studied for marine communities. In contrast, we know very little about long-term dynamics of freshwater diatoms, owing to a scarce pre-Pleistocene fossil record. However, freshwater and marine diatoms differ fundamentally: freshwater populations are smaller and less interconnected, freshwater habitats are ephemeral over geological time, and freshwater diatoms diversify and turn over faster than marine diatoms (see here for a good read on this topic). Thus: insights from long-term evolution of marine diatoms are not necessarily relevant for freshwater communities, and this despite the fact that the majority of diatom diversity can be found in freshwater environments. In a recent publication in Science Advances, we tackled the knowledge-gap on long-term freshwater diatom evolution by analyzing fossil and recent lacustrine sediments from Antarctica spanning the Middle Miocene (15-14 million years), Late Pleistocene (130-11.7 thousand years) and Holocene. This allowed investigating long-term dynamics in the diversity and biogeography of Antarctica’s freshwater diatom flora. Our dataset spans several major climate perturbations: 1) the Middle Miocene Climate Transition, MMCT (14 Ma), which was one of the most significant climate shifts driving Continental Antarctica’s transition from a temperate/subpolar climate to a polar desert, and 2) the Pleistocene glacial-interglacial cycles. We dovetailed our Antarctic dataset with an assessment of the contemporary freshwater diatom floras from the Northern and Southern Hemispheres, focusing on polar, alpine, and temperate sites. This allowed examining Antarctica’s diatom flora in a global context. We found that Miocene Continental Antarctica was home to a diverse and unique freshwater diatom flora, which was much more species rich than Continental Antarctica today. We found 212 morphospecies belonging to 49 genera. Furthermore, our Miocene diatom flora was dominated by species and genera that are present-day absent from Continental Antarctica. In fact, most of the species are new to science, and we have evidence for four new diatom genera! Using our global dataset on genus-level, we found that the Miocene flora is compositionally distinct from modern Continental Antarctica, but instead shows clear affinity with modern Arctic and Sub-Antarctic samples, as well as temperate lakes of the Southern Hemisphere. Even more exciting: we found three diatom taxa in the Miocene Antarctic material which today are confined to Antarctica’s neighboring continents. This shows that Antarctica’s Miocene diatom flora was evolving in tandem with other former Gondwanan landmasses! Strikingly, whereas Miocene Antarctica was, like the modern Arctic, home to predominantly aquatic taxa, modern Continental Antarctica is dominated by aerophiles, i.e., diatoms that preferably inhabit soils. This is indicative of a large shift in community composition that happened since the Middle Miocene. Our Miocene flora is thus witness of major, but selective, extinction among an ancient Antarctic diatom flora, likely in response to the MMCT. We hypothesize that aerophilic diatoms were more likely to survive cooling, because they are adapted to extreme conditions (see this, this and this study). However, extinction did not stop at the MMCT! Several diatoms became locally extinct in Continental Antarctica during the last glacial period. Today, such species are confined to sub-Antarctica and Maritime Antarctica, but they inhabited Continental Antarctica during the previous interglacial. Altogether, our data showed that extinction has been a dominant factor shaping Antarctic diatom communities since the Middle Miocene, resulting in the depauperation of the modern Antarctic diatom flora. However, in situ speciation and new colonizations ultimately shaped Antarctica’s highly adapted flora, which shows high levels of endemism (see also this study). In fact, molecular phylogenies of Antarctic diatoms are directly indicative of post-MMCT colonizations and local diversification. This is nicely illustrated for the diatom species complex surrounding Pinnularia borealis (see this study). Last but not least, our results provide a more holistic view on the scale of biodiversity turnover in ancient Antarctica than the fragmentary perspective offered by macrofossils, and underscore the sensitivity of lacustrine microbiota to large-scale climate perturbations. Pinseel E., Van de Vijver B., Wolfe A.P., Harper M., Antoniades D., Ashworth A.C., Ector L., Lewis A.R., Perren B., Hodgson D.A., Sabbe K., Verleyen E., Vyverman W. Extinction of austral diatoms in response to large-scale climate dynamics in Antarctica. Science Advances 7: eabh3233. full text Soil micro-organisms drive the biogeochemical cycles that underlie essential ecosystem functions. Yet, we are only beginning to grasp the drivers of terrestrial protist diversity and biogeography. This is especially true for soil protists, which have been little studied. In a new paper just published in Nature Communications, we used the diatom species complex Pinnularia borealis as a case study for the diversification and biogeography of terrestrial protists. Pinnularia borealis is an easily recognizable diatom that can be found living in soils and mosses on all continents. Although P. borealis is globally distributed, it is locally rare, meaning that it rarely generates large population sizes. Using a metabarcoding dataset, we found that its abundance, relative to other protists, is usually very low, indicating it is a rare biosphere taxon. To understand the global diversity of P. borealis, we built a global database comprising >1500 samples. Samples were collected all over the world, but the focus was directed towards temperate European regions, as well as the High Arctic and Antarctica. All samples were manually screened in a light microscope, and whenever P. borealis was observed, single cells were isolated, building a collection of >800 monoclonal cultures. The cultures were sequenced for two fast-evolving genes (28S and cox1). These fast evolving genes were then used to assess species boundaries in the complex. Using automated molecular species delimitation methods, we found evidence for at least 126 P. borealis species within our dataset. The majority of these are morphologically cryptic. Inter- and extrapolation of the species accumulation curve suggests that the global diversity of P. borealis is substantially higher than here uncovered. There might be hundreds of species hiding across the planet. Our study thus only shows the tip of the iceberg! Using a time-calibrated phylogeny, we showed that P. borealis started diversifying around the Eocene/Oligocene global cooling (ca. 25-36 Ma). This period was characterized by a profound change in climate, as the Earth shifted from a greenhouse to an icehouse state and known as a time of large-scale extinction and floral and faunal turnover. This period also marks the onset of a global expansion of open terrestrial landscapes, associated with colder and drier climates, in which P. borealis currently thrives. We found diversification in P. borealis to be largely driven by colonization of novel geographic areas and subsequent evolution in isolation. We found high levels of founder event speciation, and highlight the existence of intraspecific phylogeographic structuring. Altogether, these results illuminate our understanding of how protist diversity, biogeographical patterns, and members of the rare biosphere are generated, and suggest allopatric speciation to be a powerful mechanism for diversification of micro-organisms. Pinseel E., Janssens S.B., Verleyen E., Vanormelingen P., Kohler T.J., Biersma E.M., Sabbe K., Van de Vijver B. & Vyverman W. (2020) Global radiation in a rare biosphere soil diatom. Nature Communications 11: 2382. full text Diatoms have long been recognized for their large biotechnological potential. In the wake of growing research interest in new model species and development of commercial applications, there is a pressing need for long-term preservation of diatom strains. While cryopreservation using dimethylsulfoxide (DMSO) as a cryoprotective agent is the preferred method for long-term strain preservation, many diatom species cannot be successfully cryopreserved using DMSO. To improve existing cryopreservation protocols, my colleagues and I studied cryopreservation success in six different diatom species, representing the major morphological and ecological diatom groups. We used a range of DMSO concentrations as well as Plant Vitrification Solution 2 (PVS2) as an alternative cryoprotectant to DMSO. In addition, we tested whether suppressing bacterial growth by antibiotics accelerates the post-thaw recovery process. Our results show that the effects of cryoprotectant choice, its concentration and the addition of antibiotics are highly species specific. In addition, we showed that PVS2 and antibiotics are useful agents to optimize cryopreservation of algae that cannot survive the traditional cryopreservation protocol using DMSO. From these experiments, it became clear that a species-specific approach will remain necessary to develop protocols for diatom cryopreservation and to increase their representation in public culture collections. Stock W.*, Pinseel E.*, De Decker S.*, Sefbom J.*, Blommaert L., Chepurnova O., Sabbe K. & Vyverman W. Expanding the toolbox for cryopreservation of marine and freshwater diatoms. Scientific Reports 8: 4279. full text (*shared first authors) |