"Two layers of chance associated with spatially expanding populations: How demographic noise and environmental heterogeneity shape the evolutionary path of a population"
In nature, populations expand into new habitat at different spatial and temporal scales. The expansion process can thereby affect the evolutionary path of the growing population, a topic that has gathered much interest recently. The effects of environmental heterogeneity on the evolutionary dynamics of such range expansions remains poorly understood so far - not least due to the large variety of environmental heterogeneity found in nature. We investigate these effects in two different scenarios: neutral evolution of an expanding population and emergence of a new genotype that can spread exclusively in parts of the environment. Specifically, we first consider the effects of isolated obstacles and hotspots as well as bumps in an otherwise flat habitat. The former two are regions which hinder and accelerate the invasion, respectively. We find that those structures have characteristic consequences for neutral genetic diversity. We observe an additional layer of ‘survival of the luckiest’ – complementary to, yet qualitatively different from, founder effects occurring in the presence of 'spatial bottlenecks'. Second, we investigate the establishment of a new genotype that we allow to spread exclusively in some parts of the environment but constrain to have a selective disadvantage elsewhere. We describe the role that environmental structure has in shaping the fate of this new genotype.
H. Lee Moffitt Cancer Center
"Time scales and wave formation in non-linear spatial public goods games"
Evolutionary public good (PG) games capture the essence of production of growth-beneficial factors that are vulnerable to exploitation by free-riders who do not carry the cost of production. PGs emerge in cellular populations, for example in growing bacteria and cancer cells. We study the eco-evolutionary dynamics of a PG in populations that grow in space. In our model, PG-producer cells and free-rider cells can grow according to their own birth and death rates. Co-evolution occurs due to public good-driven surplus in the intrinsic growth rates at a cost to producers. A net growth rate-benefit to free-riders leads to the well-known tragedy of the commons in which producers go extinct. What is often omitted from discussions is the time scale on which this extinction can occur, especially in spatial populations. Here, we derive analytical estimates of the ε-extinction time in differ- ent spatial settings. As we do not consider a stochastic process, the ε-extinction time captures the time needed to approach an extinction state. We identify spatial scenarios in which extinction takes long enough such that the tragedy of the commons never occurs within a meaningful lifetime of the system. Using numerical simulations we analyze the deviations from our analytical predictions.
University of Campinas
"Modeling Mito-nuclear Compatibility and Its Role in Species Identification"
Mitochondria play a key role in population genetics and evolutionary biology. Praised as a reliable genetic marker, the utility of mtDNA derives from its particular molecular properties, including high evolutionary rate, uniparental inheritance, and small size. Such properties make the mtDNA a powerful substrate for inferring geographic structure of populations and phylogenetic relationships. An important application is the use of a standardized segment of the mtDNA for species identification in animals, called the DNA barcode. The high rate of success to distinguish both phylogenetically close and distant species of vertebrates motivates a fundamental question: why does the barcode work and how does it relate to the nuclear DNA (nDNA) divergences during speciation? Nuclear and mitochondrial DNA’s interact during the respiration process, which depends on the coordination of genes from both sources. Recent observations of coevolution between these genomes suggest that this genetic interaction affects organism fitness; thus, mtDNA may play a fundamental role in speciation. Here we study how mito-nuclear interactions affect the speciation process and whether the accuracy of species identification by mtDNA is a consequence of the mito-nuclear coevolution. We investigate the validity of mtDNA-based barcoding in an evolving population, comparing the classification provided by mtDNA with the classification based on nuclear genetic content. Starting from an individual-based model for spatially distributed populations, we simulate the evolution of a population of individuals who carry a recombining nuclear genome and a mitochondrial genome inherited maternally. We compare a null model fitness landscape that lacks any mito-nuclear interaction against a scenario in which interactions influence fitness. Fitness is assigned to individuals according to their mito-nuclear compatibility, which drives the coevolution of the nuclear and mitochondrial genomes. Depending on the model parameters, the population breaks into distinct species and the model output then allows us to analyze the accuracy of mtDNA barcode for species identification depending on the selection strength over the mito-nuclear compatibility. We also register the signatures left in the genetic content and spatial distribution of the populations due to selection imposed on mito-nuclear compatibility. These analyses allow us to evaluate the effects of mito-nuclear interaction on the diversification process and examine to what extent mito-nuclear coevolution assists speciation.