Dynamic fitness and horizontal gene transfer in stochastic evolutionary dynamics

by Hinrich Arnoldt
Doctoral thesis
Date of Examination:2013-01-28
Date of issue:2013-03-12
Advisor:Prof. Dr. Marc Timme
Referee:Prof. Dr. Marc Timme
Referee:Prof. Dr. Theo Geisel
Persistent Address: http://dx.doi.org/10.53846/goediss-3770

 

 

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Abstract

English

The evolution of species is shaped by processes such as selection, mutations or genetic drift. Still, we are far away from a complete understanding of how these processes drive evolutionary dynamics in detail. Therefore, we need basic models which capture the essence of evolutionary dynamics to understand the mechanisms underlying evolution. The basis of many such models is the so-called fitness of the individuals which measures how many offspring a certain individual will produce. Often, such fitness is assumed to be constant over time, although interactions between different individuals can lead to dynamically changing fitnesses. Here, we analyze the evolutionary dynamics of a population exhibiting such dynamic fitness. Our results reveal that dynamic fitness can lead to evolutionary dynamics which stochastically switch between multiple stable points. Furthermore, in the last decades an increasing evidence has been found that apart from selection, mutation and genetic drift another process drives evolution. This process is horizontal gene transfer (HGT), i.e. the exchange of genetic material between individuals of one generation. However, how evolution proceeds under the influence of HGT is still unclear. Here, we provide a new model for HGT and show how it drives evolutionary dynamics in populations exhibiting a high or a low competence for HGT. We demonstrate how frequently occuring HGT can lead to an evolutionary state where no distinct species can be distinguished. Thus, our work points toward a probable mechanism how the first species may have emerged from a primordial reactive soup in which no species existed and individuals exchanged genes frequently via HGT.
Keywords: Evolution; Dynamic fitness; Horizontal gene transfer; Individual-based models; Stochastic dynamics; Emergence of first species
 
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