Cardiocondyla obscurior strain:BR alpha Variation

Trait variation between populations is a result of selection, genetic drift, or a combination of both. Adaptive evolution is based on selection of alternative phenotypes, implying heritable variation at the genotypic or epigenetic level. Genetic drift on the other hand results in a random distribution of genotypes drawn from a source population. We studied phenotypic differences and analyzed the genome of two introduced populations of the invasive ant Cardiocondyla obscurior to understand how variation is generated. In comparison to other sequenced ants, several subclasses of transposable elements (TEs) have selectively proliferated in C. obscurior. The genome is structured into low-density regions (LDRs) and distinct TE islands that comprise 7.18% of the genome and range between 0.19 and 1.46 Mb. TE islands evolve faster than LDRs with regard to SNVs, gene/exon duplications/deletions, and degree of orthology. A non-random distribution of gene families, larvae/adult specific expression of genes and signs of stronger past methylation in TE islands compared to LDRs indicate different degrees of evolutionary rates and differences in effective population size within the genome. We argue that TE islands have formed through genetic drift and have subsequently become adaptive by generating a substantial proportion of the genetic diversity and thus provide additional leverage for selection. Our approach allows studying genome evolution dynamics in response to drift and inbreeding in a species that successfully colonizes novel habitats.