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FRIMEDBIO-Fri med.,helse,biol

ERC-Stenseth Red Queen coevolution in multispecies communities: long-term evolutionary consequences of biotic and abiotic interactions

Awarded: NOK 13.7 mill.

A major unsolved question at the heart of evolutionary biology is "What is the relative importance of biotic and abiotic forces in the evolution of multispecies communities?" Our project addresses this fundamental question and connects it to Van Valen's classical Red Queen Hypothesis (1973), which suggests that biotic interactions among species result in a continued evolutionary race over geological time scales. Although Van Valen recognized the evolutionary importance of abiotic forces, he suggested that biotic interactions among species alone suffice to keep biological systems evolving, with mutation and selection leading to a continual process of adaptation. The viewpoint that biotic interactions drive evolutionary change is widespread among evolutionary biologists, many of whom study the influence of biotic interactions on short-term evolutionary dynamics. Alternatively, it has been suggested that abiotic factors are the main drivers of evolutionary dynamics, provoking speciation and extinction, and that biotic interactions barely affect evolutionary fine-tuning. This view is especially common among palaeontologists whose studies span geological time scales. Direct analyses of the effects of biotic interactions are often neglected in palaeontological studies, perhaps because of the complexity of the task. An important part of the project so far has been to come up with testable predictions tat can disentangle the relative effects of biotic and abiotic factors on evolutionary patterns. This work is both done by developing theoretical models, but does also consist of finding empirical systems where it is possible to test various hypotheses for what drives the evolutionary changes in the system. The theoretical part of the work has progressed rather much over the last year. Several types of model frameworks are being explored in order to investigate if a few common processes are always needed to enable Red Queen dynamics in ecosystems on macroevolutionary time scales. An important part of this work is to investigate already published models in the literature in order to check if these hinge on dubious assumptions. Another important part of the project involves studying the evolutionary outcome of competition between individuals in the fossil record. Bryozoa is a phylum within animals. They are aquatic invertebrates with a hard skeleton, which makes them fossilize very easily. Bryozoa fight for space at their substrate (e.g. mollusks) and this competition is possible to study in the fossil record. This gives a unique opportunity to observe which species that interacted in deep time, and if the outcome of this competition had any evolutionary effects. The first paper on ecological interaction on macroevolutionary time scales has recently been published. This paper shows that most species do not change their competitive ability much on million-year time scales, while only a hand-full of species changes their ability to compete with individuals from other species. A new study on the bryoza-system shows that body size is a good predictor of competitive outcome between species and that bigger species win competitive interactions more often than smaller species. However, we find no indications that smaller species have a higher risk of going extinct on million-year time scales, suggesting other factors than size must also be important for understanind species survival on macroevolutionary time scales. Two teoretical studies have been published. The first study shows that asymmetry in competitive effects between species are common and that this asymmetry is necessary for contionous evolution due to biotic factors alone when the abiotic part of the environment is not changing. The second theoretical study represents a new general model for understanding how macroevolutionary change can be partitioned into three components: (i) ecologically driven change, (ii) evolutionarily driven change, and (iii) environmentally driven change.

While both biotic factors, such as competition, and abiotic factors, such as changing climate, are usually acknowledged to contribute to evolutionary change and biotic turnover, their relative contributions remain unknown. In 1973, Leigh Van Valen publish ed his Red Queen hypothesis, suggesting that in a multispecies system without any abiotic perturbations, evolution would still continue. He hypothesized that biotic interactions between species alone suffice to force biological systems into a never-settli ng evolutionary race. Although almost 40 years have passed, empirical validation of Van Valen?s hypothesis is still pending and the importance of biotic interactions for long-term evolutionary dynamics remains unclear. To bridge this gap in our knowledge, I propose a novel two-pronged approach. Together with my team I will apply novel analyses of palaeontological data that explicitly account for preservation and sampling processes and that simultaneously examine both biotic and abiotic factors in evolutio nary turnover. Concurrently, we will develop a collection of novel mechanistic mathematical models that integrate ecology that are shaped towards specific systems for which we have long-term data. Empirical results from our statistical modelling of palaeo ntological data will be used to inform our collection of models. The mathematical models we will develop will explicitly account for organisms? interactions with both one another and the environment. They will allow us to disentangle the effects of possib le drivers of Red Queen dynamics one by one. As results accumulate, the analyses of empirical data and mathematical modelling will benefit from each other in an iterative process of mutual feedback. The proposed research will result in fresh understanding of the contribution of biotic interactions and abiotic influences on the long-term evolution of lineages.

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FRIMEDBIO-Fri med.,helse,biol