Genetics of diapause termination timing in the water flea Daphnia - identifying genes and evolutionary processes of relevance in nature

点击翻译按钮获取中文摘要

In seasonal environments, the life cycle of many organisms is characterized by a period of dormancy. This allows surviving unfavourable conditions until dormancy is terminated upon the onset of the next growth season. In the water flea Daphnia, a crustacean zooplankter that is a pivotal herbivore in standing waters, this is realised through the production of diapausing eggs.The exact timing of diapause termination is a fitness relevant life history phenotype which is adaptively differentiated between habitats. Empirical evidence suggests that natural populations adapt to current climate change by the modification of such timing rather than shifting their thermal optima or tolerance. There is a need to reveal the genetic architecture in control of this timing in order to understand how this trait can evolve in natural populations. Here, we present a research strategy to reveal the genetic architecture controlling the timing of release from diapause in Daphnia. This will be achieved through gene mapping followed by further characterization and validation of the resulting candidate loci. The prevalence of genetically based timing differentiation in nature will be assessed for populations over a latitudinal gradient and on a micro-geographic scale. In order to test whether adaptive differentiation of this trait in nature is caused by the repeated recruitment of the same genes and pathways, association studies using the candidate loci will be performed. Additionally, the source of adaptive alleles and mechanisms of adaptive evolution will be traced using a paleogenomics approach. In Daphnia, this is feasible through the analysis of diapause resting stages which are preserved in sediments. We will sequence candidate loci and assess the genetic background through neutral markers in ancestral founding populations and derived populations. Using these data, we will determine if divergence in diapause release timing evolves via (a) selection from standing genetic variation in the founding populations (b) admixture and introgression of advantageous alleles into a resident population's genetic background or (c) de novo mutation in highly variable genomic regions.