Here, we will use genomic methods to understand what maintains the abundant genetic variation observed in natural field populations, a central question in evolutionary biology. Fluctuating selection is a mechanism of balancing selection where the strength and direction of selection vary over time in response to environmental fluctuations. Natural populations constantly experience temporally fluctuating environments from variation in temperature, rainfall, resource availability, and the abundance of predators, competitors or parasites. Most life-history traits are typically controlled by multiple genes (polygenic inheritance), and many organisms are likely to encounter seasonally fluctuating selection acting on traits coded by a large part of their genome, resulting in an important role for fluctuating selection as a mechanism for maintaining genetic variation. If such fluctuating selection varies in direction across generations, different alleles will be advantageous at different time points, maintaining both alleles in the population over long time periods, despite being subject to directional selection. Similarly, if the direction of selection changes across the life cycle, where for example, specific life cycle stages are crucial for survival and others for reproduction, it can give rise to conflicting selection between life stages. Understanding how fluctuating selection and conflicting selection between life stages maintains genomic diversity offers valuable insights into the fundamental mechanisms driving evolution within natural populations. Despite its significance, this area of study remains relatively unexplored and where most previous research has focused on one model organism: the fruit fly (Drosophila melanogaster). In this project, we will use the Common Bluetail Damselfly (Ischnura elegans), as our model organism. This is an insect species with three heritable female colour morphs were we recently discovered the position of the autosomal molecular locus. We have access to 27 years of long-term data on ecological and evolutionary dynamics and access to a high-quality chromosome-level reference genome of I. elegans, enabling in-depth genomic research. To achieve our goals, we will sequence 1034 wild-caught individuals including males and females across life stage (i. e. larvae vs. adults) and years. These data include three consecutive years for the adult stage and across 2 consecutive years for the aquatic stage. We have spatial replication from four independent populations to enable us to quantify how genome-wide allele frequencies respond to different selection regimes between life stages and across generations, shaping genome-wide diversity in a semi-aquatic insect species where the aquatic larvae and the terrestrial adults encounter drastically different environments. In late August or early September 2026, we will receive 4000 GiB of new raw sequence data. Together with a previous pilot study of ours, we estimate that we will need a minimum 26000 GiB data, excluding any extra analysis. We therefore apply for 30 000 GiB of storage associated with this Medium Compute Project.