Abstract
Genomics is a powerful toolkit for unravelling how evolutionary processes drive organisms’ small- and large-scale genetic variation. Several outstanding questions remain concerning the evolution of genome size and architecture, especially in intracellular parasites. Microsporidia became a model for this field of study as they exhibit genome size variation of more than an order of magnitude. Here, we discuss evolution in the large-genome microsporidium Hamiltosporidium tvaerminnensis , a parasite of a water flea.