Genetic paradox of invasions in Tetramorium ants

Biological invasions, the transfer of species from native ranges to regions where they had been absent and their subsequent spread over the non-native ranges are an increasingly threatening facet of global change. Invasive species cause ecological catastrophes in that they replace native species and thus trigger losses of biodiversity, alter the structure and functioning of whole ecosystems and spread infectious diseases. Biological invasions also cause immense economic losses. From the view of population biology the overwhelming success of invasive species is counterintuitive because the introduction of initially one or few individuals poses a severe bottleneck. Such bottlenecks should lower the viability of a population due to inbreeding, and should preclude the evolution of local adaptation due to a lack of the necessary genetic variation. Hence, the success of invasive species has been coined a "genetic paradox". The project addresses the genetic paradox by investigating two closely related pavement ants, Tetramorium sp.E (widely known as T. caespitum) and T. tsushimae, both of Palearctic origin, and both invasive in North America. The two ants have differing life history strategies, single-queened colonies strictly separated from each other in T. sp.E, but multi-queened colonies which often are scattered over large areas in T. tsushimae. In this T. tsushimae closely approaches unicoloniality, which is the complete absence of colony barriers and which is considered to trigger invasion success in many ants. By mitochondrial DNA sequencing and genotyping of a high number of microsatellite loci of samples from the entire known native and non-native ranges I aim at resolving the invasion histories of the two species, especially the number of introductions and the degree of admixture within the non- native ranges. I will use the genomic information content approach as a conceptual framework for data interpretation by expanding it to non-coding DNA and by including the estimators for genetic diversity established in population genetics. The competing hypotheses of decrease versus increase of the genomic information content in non-native relative to native ranges will be evaluated for each species. The results of the integrative analysis should elucidate how the two pavement ants have solved the genetic paradox. Evaluation of the hypotheses will subsequently allow balancing the relative importance of life history and invasion history in shaping the genomic information content of the invasive populations. Any of four possible scenarios will help to shed light on whether generalizations on the genomic information content of invasive populations are feasible or whether species specific combinations of factors have to be expected. The results will also tie into the current debate on the role of the genetic makeup of populations in the establishment of unicoloniality. The prospective answers on all these questions will be useful for the development of algorithms predicting success of invasions. In conclusion, the project will be of relevance to advance in population biology, social evolution research, and practical control of biological invasions.