Project

Discipline

paleoecology; ecosystem evolution; aDNA; paleogenomics; cichlid fish; adaptive radiation; ecosystem ecology; climate change

Lead
Der Ostafrikanische Viktoriasee hat sich nach einer Austrocknungsperiode vor 15’000 Jahren wieder gefüllt. In geologisch kurzer Zeit haben sich dort hunderte Buntbarscharten gebildet, eine wahre ‘Artenexplosion’. Unser Projekt untersucht die Umweltbedingungen während dieser adaptiven Radiation und wie das Ökosystem durch neu entstandene Arten beeinflusst wurde.
Lay summary
Inhalt und Ziele des Forschungsprojekts Wie die Zu- oder Abnahme von Biodiversität durch Entstehen oder Aussterben von Arten Ökosysteme verändert ist noch wenig bekannt. Ob und wie solche Veränderungen das Entstehen oder Aussterben weiterer Arten begünstigen oder behindern ist ebenfalls wenig erforscht. Das Projekt wird die Wechselwirkungen zwischen der Diversifizierung der Buntbarsche und dem Gesamtökosystem anhand von Sedimentbohrkernen über die Zeit hinweg untersuchen. Die Häufigkeit und Artenzusammensetzung verschiedener Organismengruppen in der Vergangenheit wird dazu aus in Sedimenten abgelagerten Überresten und alter DNA rekonstruiert. Vertiefte paleogenetische Analysen von Fischknochen sollen die Entstehungszeit und genetische Basis der Buntbarschvielfalt aufzeigen: Wie beispielsweise die Verfügbarkeit einer neuen Nahrungsressource eine neue Spezialisierung begünstigte, und wie eine solche Spezialisierung in Folge die Artengemeinschaft veränderte. Wissenschaftlicher und gesellschaftlicher Kontext des Forschungsprojekts Das Projekt betrachtet grundlegende Mechanismen der Evolution und Ökologie und deren Zusammenspiel. Ein besseres Verständnis dieser komplexen Dynamiken ist gerade im Hinblick auf den weltweit gegenwärtig raschen Verlust von Biodiversität und Veränderung von Ökosystemen von grosser Wichtigkeit. Key words Diversification, ecology, evolution, ecosystem, feedbacks, cichlid fish

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Last update: 19.02.2019

Natural persons

Number	Title	Start	Funding scheme

The mutual influence between the biodiversity and the structure and functioning of ecosystems is a central and pressing question at the interface between evolutionary ecology and environmental sciences. Evolution is a population dynamic process that plays out in an ecosystem context of changing species interactions and abiotic conditions. Reciprocal interactions between evolutionary and ecosystem processes are fundamental for understanding the origin, assembly, and maintenance of species diversity, spanning micro- and macroevolutionary timescales. However, tracking such dynamics in natural ecosystems over long periods of time is largely out of reach for most research programs. Here, we have assembled a highly innovative and interdisciplinary research team that will deploy an integrative paleobiological approach to dig back into time and reconstruct the evolutionary history of the Lake Victoria ecosystem. Among the East African Great Lakes, Lake Victoria harbours one of the most globally impressive examples of the rapid origination of hundreds of new fish species through the processes of speciation and adaptive radiation. An entire endemic food web has assembled over the Holocene, and is comprised of fish species with adaptations to a multitude of ecological niches (Fig. 1). Decades of research on this cichlid dominated food web have revealed key mechanisms of speciation and ecological adaptation - fundamental processes omnipresent across the tree of life. Less often appreciated is that cichlid fish dominate not only the biodiversity but also the biomass of this food web, and hence provide a unique system to study the interdependencies between biodiversity dynamics and ecosystems over evolutionary timescales. So far, work on this global hotspot of freshwater biodiversity has only considered extant biodiversity. Information coupling fossil assemblages with past environments is lacking, severely limiting our understanding about the timing of the emergence of new ecological guilds of fish, and possible feedbacks between the rapid evolution of food web complexity and ecosystem dynamics. Because Lake Victoria and its endemic species diversity are only about 15,000 years old, evolutionary and ecosystem dynamics are unfolding at broadly overlapping time scales, making it possible to couple paleoecological, paleontological and paleogenomic reconstruction methods. The Lake Victoria ecosystem has also undergone dramatic environmental changes over the past 15,000 years, which have been documented with classical paleolimnological approaches. We recently discovered fish fossils in large abundance in previous sediment cores dating back to the filling of the lake during the last glacial-interglacial transition. These fossils can be used to reconstruct past species assemblages of fish in considerable detail in order to study ecological and evolutionary changes through time (Fig. 2, Fig. 3). Combining this with information about past environmental conditions, recorded in the same layers of those same sediment cores, we can make exciting and novel reconstructions using a wide range of paleoecological and limnological proxies. We have already obtained funding for a coring expedition to Lake Victoria in the summer of 2018 to collect a series of piston cores along an onshore-offshore gradient in Lake Victoria, which will likely yield tens of thousands of fossil fish teeth, bones and scales, as well as fossils of other organisms. Here we apply for an interdisciplinary investigation of these new cores, and further cores to be taken in the proposed project, in order to perform detailed reconstructions of past ecosystems from the filling of the lake to the modern day. We will combine this with detailed ecological, evolutionary and genomic analyses of the evolving fish assemblage as it changed over millennia from one with few species to one with hundreds of endemic species. Through finely resolved time series of ecosystem properties and biodiversity, we will for the first time be able to ask how external drivers of the ecosystem affected the evolution and ecology of a species assemblage, whether the changes in the species assemblage affected the ecosystem and whether there were feedback loops between the two. At the same time, we will be able to study in detail the ecosystem changes associated with lake eutrophication and mass extinction in the Anthropocene of Lake Victoria.