Adaptive Species

Abstract

One of the most challenging issues in evolutionary biology is the synthesis of population-level dynamics (microevolution) with large-scale speciation patterns (macroevolution). Although this idea was formulated as part of the Evolutionary Synthesis in the 1930s, global variations in species richness or findings from fossil records still seem partially inconsistent with the predictions based on biotic interactions. This indicates, that the selective processes at work are not yet sufficiently understood.

While historically biologists mainly tried to examine the upward causation, from organisms to species, the accompanying, downwards directed feedback loop is a hugely neglected topic: the influence of macroevolution on organismic traits. This feedback loop is especially interesting if the traits that are affected by its effect, are simultaneously those that caused the loop to start in the beginning: traits that are associated with variations in speciation and extinction rates. My thesis revolves around a series of biological questions connecting to this observation: What is the nature of species; do they really exist? If they do, can species constitute a unit of selection? Does selection among species affect speciation or extinction rates? Which traits play a major role in causing this variation?

To address these questions, I conceptualized the integration of selection at the species level into speciation theory, not only as pattern but as a process. In a case study, I modelled the evolution of sexual reproduction, a trait which is commonly assumed to increase net-diversification rates of species. Therefore, I developed an agent-based simulation framework to study the evolution of species-level traits. Based on an adaptive dynamics model for ecological diversification, I could show that assortative mating in sexually reproducing populations enables the emerging ‚sympatric‘ demes to maintain a higher diversity compared to asexuals. The results do not only highlight the relevance of multi-level selection processes for macroevolution but also contribute to the long standing question why sex evolved despite for its costs for the individual.